Table of contents

This paper constructs a theoretical framework for calculating the distribution of masses for gas giant planets forming via the core accretion paradigm. Starting with known properties of circumstellar disks, we present models for the planetary mass distribution over the range 0.1M_J ≤ M_p < 10M_J. If the circumstellar disk lifetime is solely responsible for the end of planetary mass accretion, the observed (nearly) exponential distribution of disk lifetime would imprint an exponential falloff in the planetary mass function. This result is in apparent conflict with observations, which suggest that the mass distribution has a (nearly) power-law form of ${dF}/{{dM}}_{{\rm{p}}}\sim {M}_{{\rm{p}}}^{-p}$, with an index of p ≈ 1.3, over the relevant planetary mass range (and for stellar masses ∼0.5–2M_⊙). The mass accretion rate onto the planet depends on the fraction of the (circumstellar) disk accretion flow that enters the Hill sphere, and on the efficiency with which the planet captures the incoming material. Models for the planetary mass function that include distributions for these efficiencies, with uninformed priors, can produce nearly power-law behavior, consistent with current observations. The disk lifetimes, accretion rates, and other input parameters depend on the mass of the host star. We show how these variations lead to different forms for the planetary mass function for different stellar masses. Compared to stars with masses M_* = 0.5–2M_⊙, stars with smaller masses are predicted to have a steeper planetary mass function (fewer large planets).

The Sun produces highly dynamic and eruptive events that can drive shocks through the corona. These shocks can accelerate electrons, which result in plasma emission in the form of a type II radio burst. Despite the large number of type II radio burst observations, the precise origin of coronal shocks is still subject to investigation. Here, we present a well-observed solar eruptive event that occurred on 2015 October 16, focusing on a jet observed in the extreme ultraviolet by the Atmospheric Imaging Assembly (SDO/AIA), a streamer observed in white light by the Large Angle and Spectrometric Coronagraph (SOHO/LASCO), and a metric type II radio burst observed by the LOw Frequency Array (LOFAR). LOFAR interferometrically imaged the fundamental and harmonic sources of a type II radio burst and revealed that the sources did not appear to be cospatial, as would be expected from the plasma emission mechanism. We correct for the separation between the fundamental and harmonic using a model that accounts for scattering of radio waves by electron density fluctuations in a turbulent plasma. This allows us to show the type II radio sources were located ∼0.5R_⊙ above the jet and propagated at a speed of ∼1000 km s⁻¹, which was significantly faster than the jet speed of ∼200 km s⁻¹. This suggests that the type II burst was generated by a piston shock driven by the jet in the low corona.

A complete understanding of solar radio bursts requires developing numerical techniques that can connect large-scale activities with kinetic plasma processes. As a starting point, this study presents a numerical scheme combining three different techniques: (1) extrapolation of the magnetic field overlying a specific active region in order to derive the background field, (2) guiding-center simulation of the dynamics of millions of particles within a selected loop to reveal the integral velocity distribution function (VDF) around certain sections of the loop, and (3) particle-in-cell simulation of kinetic instabilities driven by energetic electrons initiated by the obtained distributions. Scattering effects at various levels (weak, moderate, and strong) due to wave turbulence-particle interaction are considered using prescribed timescales of scattering. It was found that the obtained VDFs contain strip-like and loss-cone features with positive gradient, and both features are capable of driving electron cyclotron maser emission, which is a viable radiation mechanism for some solar radio bursts, in particular, solar radio spikes. The strip-like feature is important in driving the harmonic X mode, while the loss-cone feature can be important in driving the fundamental X mode. In the weak-scattering case, the rate of energy conversion from energetic electrons to X2 can reach up to $\sim 2.9\times {10}^{-3}\,{E}_{{k}_{0}}$, where ${E}_{{k}_{0}}$ is the initial kinetic energy of energetic electrons. The study demonstrates a novel way of exciting the X2 mode in the corona during solar flares and provides new sight into how escaping radiation can be generated within a coronal loop.

Because mergers of black hole–neutron star (BH–NS) binaries are widely argued to produce both gravitational and electromagnetic waves, these binaries are among the most attractive systems in the era of multi-messenger astronomy. In this paper we explore the charging processes of a moving BH in two types of charged surroundings and propose a new charging scenario differing from the elegant mechanism of Wald. During the inspiral of such a binary, the NS is strongly magnetized and the BH is moving inward. By considering this moving BH charging scenario, we find that the BH will increasingly accumulate enough net charge to light up the binary system at the inspiral stage. This charging process is universal no matter whether the BH spins or not. We show that our BH charging scenario can physically explain the BH's unipolar inductor mechanism in a BH–NS binary system. We calculate electromagnetic emission luminosities due to various energy dissipation mechanisms and find that the electric dipole radiation of the BH makes a dominant contribution to electromagnetic emission at the final stage of inspiral if the BH spins slowly.

We report the discovery of possible periodic X-ray dips in a pulsating ultraluminous X-ray source, M51 ULX-7, with archival Chandra observations. With ∼20 days of monitoring in the superorbital descending state, we discovered three dips with separations of ∼2 and ∼8 days via the Bayesian block technique. A phase-dispersion minimization and a ${\chi }^{2}$ test suggest that the dip is likely recurrent with a period of ∼2 days, consistent with the orbital period of M51 ULX-7. We interpret the dip as an obscuring of the emission from the pulsar by the vertical structure on the stream–disk interaction region or the atmosphere of the companion star. Both interpretations suggest the viewing angle to be ∼60°. Given that the magnetic field of M51 ULX-7 is moderately high, B ∼ 10¹³ G, a low geometric beaming with $b\gtrsim 1/2$ is sufficient to explain the observed flux and the presence of dips. Obscuration of the stellar wind remains an alternative possible origin and further monitoring of the dips will be required.

We present timing solutions for eight binary millisecond pulsars (MSPs) discovered by searching unidentified Fermi-Large Area Telescope (LAT) source positions with the 327 MHz receiver of the Arecibo 305 m radio telescope. Five of the pulsars are "spiders" with orbital periods shorter than 8.1 hr. Three of these are in "black widow" systems (with degenerate companions of 0.02–0.03 M_⊙), one is in a "redback" system (with a non-degenerate companion of ≳0.3 M_⊙), and one (J1908+2105) is an apparent middle-ground case between the two observational classes. The remaining three pulsars have white dwarf companions and longer orbital periods. With the initially derived radio timing solutions, we detected γ-ray pulsations from all MSPs and extended the timing solutions using photons from the full Fermi mission, thus confirming the identification of these MSPs with the Fermi-LAT sources. The radio emission of the redback is eclipsed during 50% of its orbital period, which is typical for this kind of system. Two of the black widows exhibit radio eclipses lasting for 10%–20% of the orbit, while J1908+2105 eclipses for 40% of the orbit. We investigate an apparent link between gamma-ray emission and a short orbital period among known binary MSPs in the Galactic disk, and conclude that selection effects cannot be ruled out as the cause. Based on this analysis we outline how the likelihood of new MSP discoveries can be improved in ongoing and future pulsar searches.

The hot and diffuse nature of the Sun's extended atmosphere allows it to persist in non-equilibrium states for long enough that wave–particle instabilities can arise and modify the evolution of the expanding solar wind. Determining which instabilities arise, and how significant a role they play in governing the dynamics of the solar wind, has been a decades-long process involving in situ observations at a variety of radial distances. With new measurements from the Parker Solar Probe (PSP), we can study what wave modes are driven near the Sun, and calculate what instabilities are predicted for different models of the underlying particle populations. We model two hours-long intervals of PSP/SPAN-i measurements of the proton phase-space density during the PSP's fourth perihelion with the Sun using two commonly used descriptions for the underlying velocity distribution. The linear stability and growth rates associated with the two models are calculated and compared. We find that both selected intervals are susceptible to resonant instabilities, though the growth rates and kinds of modes driven unstable vary depending on whether the protons are modeled using one or two components. In some cases, the predicted growth rates are large enough to compete with other dynamic processes, such as the nonlinear turbulent transfer of energy, in contrast with relatively slower instabilities at larger radial distances from the Sun.

Molybdenum isotopes measured in most individual presolar silicon carbide grains are dominated by s-process contributions from the helium intershells of asymptotic giant branch (AGB) stars. The much smaller isotopic variations in molybdenum in meteorites and their components are largely controlled by s-process enrichments or depletions relative to terrestrial composition but lie along two parallel s-process mixing lines separated by what has been suggested to be an r-process contribution. The two mixing lines are populated by carbonaceous-chondrite- and noncarbonaceous-chondrite-related meteorites (CC and NC groups, respectively). We have compared molybdenum isotopic data for presolar grains with those from meteorites and renormalized the meteorite data in a way that is consistent with s-, r-, and p-process contributions observed in presolar SiC grains. The results indicate that (1) there seems to be a fixed ratio between p- and r-process contributions in all data, (2) the dichotomy in molybdenum isotopes between the CC and NC groups can be explained by variations in the isotope makeup of the s-process contribution to the meteoritic samples, (3) this variability is similar to the variations in s-process molybdenum from different AGB stars deduced from presolar grain analyses, and (4) the larger range of isotopic compositions found in refractory inclusions is also consistent with s-process isotope variability.

The vegetation red edge (VRE) is a unique spectral fingerprint of light-harvesting vegetation on Earth and provides a robust remote detectable surface biosignature of exoplanets. To improve the detectability and sensitivity, we have studied the diurnal variability of VRE in the disk-integrated spectra of Earth and also Earth analogs in the case of different observing geometry conditions. Simulation results show that the VRE index varies from <−0.4 to >0.6 at a diurnal timescale for both present and also Late Triassic Earth, and the maximum variation of VRE in 1 day changes by >3 times with different observing geometry conditions. This means that the extraterrestrial light-harvesting vegetation (even if it really exists) will not be efficiently detectable without proper observing geometry conditions and time, especially in the case of the exoplanets covered with thick clouds. The VRE temporal variation curve can also be used to retrieve the cloud cover fraction and continent distribution of exoplanets with relatively high precision. Several observational strategies are proposed to detect the light-harvesting vegetation and retrieve the planetary information from the planet's VRE variation signals, and a mock observation is also demonstrated.

Interchange reconnection has been proposed as a mechanism for the generation of the slow solar wind, and a key contributor to determining its characteristic qualities. In this paper we study the implications of interchange reconnection for the structure of the plasma and field in the heliosphere. We use the Adaptively Refined Magnetohydrodynamic Solver to simulate the coronal magnetic evolution in a coronal topology containing both a pseudostreamer and helmet streamer. We begin with a geometry containing a low-latitude coronal hole that is separated from the main polar coronal hole by a pseudostreamer. We drive the system by imposing rotating flows at the solar surface within and around the low-latitude coronal hole, which leads to a corrugation (at low altitudes) of the separatrix surfaces that separate open from closed magnetic flux. Interchange reconnection is induced both at the null points and separators of the pseudostreamer, and at the global helmet streamer. We demonstrate that a preferential occurrence of interchange reconnection in the "lanes" between our driving cells leads to a filamentary pattern of newly opened flux in the heliosphere. These flux bundles connect to but extend far from the separatrix-web (S-Web) arcs at the source surface. We propose that the pattern of granular and supergranular flows on the photosphere should leave an observable imprint in the heliosphere.

HH 211 is a highly collimated jet with a chain of knots and a wiggle structure on both sides of a young Class 0 protostar. We used two epochs of Atacama Large Millimeter/submillimeter Array (ALMA) data to study its inner jet in the CO(J = 3–2), SiO(J = 8–7), and SO(N_J = 8₉–7₈) lines at ∼25 au resolution. With these ALMA and previous 2008 Submillimeter Array data, the proper motion of 8 knots within ∼250 au of the central source is found to be ∼0068 per year (∼102 km s⁻¹), consistent with previous measurements in the outer jet. At about four times higher resolution, the reflection-symmetric wiggle can be still fitted by a previously proposed orbiting jet source model. Previously detected continuous structures in the inner jet are now resolved, containing at least 5 subknots. These subknots are interpreted in terms of a variation in the ejection velocity of the jet with a period of ∼4.5 yr, shorter than that of the outer knots. In addition, backward and forward shocks are resolved in a fully formed knot, BK3, and signatures of internal working surface and sideways ejection are identified in position–velocity diagrams. In this knot, low-density SO and CO layers are surrounded by a high-density SiO layer.

We compare the molecular and ionized gas velocity dispersions of nine nearby turbulent disks, analogs to high-redshift galaxies, from the DYNAMO sample using new Atacama Large Millimeter/submillimeter Array and GMOS/Gemini observations. We combine our sample with 12 galaxies at z ∼ 0.5–2.5 from the literature. We find that the resolved velocity dispersion is systematically lower by a factor 2.45 ± 0.38 for the molecular gas compared to the ionized gas, after correcting for thermal broadening. This offset is constant within the galaxy disks and indicates the coexistence of a thin molecular gas disk and a thick ionized one. This result has a direct impact on the Toomre Q and pressure derived in galaxies. We obtain pressures ∼0.22 dex lower on average when using the molecular gas velocity dispersion, σ_0,mol. We find that σ_0,mol increases with gas fraction and star formation rate. We also obtain an increase with redshift and show that the EAGLE and FIRE simulations overall overestimate σ_0,mol at high redshift. Our results suggest that efforts to compare the kinematics of gas using ionized gas as a proxy for the total gas may overestimate the velocity dispersion by a significant amount in galaxies at the peak of cosmic star formation. When using the molecular gas as a tracer, our sample is not consistent with predictions from star formation models with constant efficiency, even when including transport as a source of turbulence. Feedback models with variable star formation efficiency, _ff, and/or feedback efficiency, p_*/m_*, better predict our observations.

The Large Magellanic Cloud supernova remnant J0454-6713 abutting the H ii region N9 has been observed with XMM-Newton. Two groups of lines from Fe xvii account for half the emission and lines from Fe xviii, O vii, and O viii are also clearly detected with the XMM RGS. Isothermal equilibrium fits of the EPIC spectra reproduce the basic spectral form and show little variation throughout the remnant but are insensitive to the lines from the high-temperature ions. These are overwhelmed in the EPIC cameras by the dominant Fe xvii radiation and the EPIC best-fit spectra do not agree with the RGS data. Uncertainties in the atomic data used to determine Fe-line strength present a further complication which inhibits a good EPIC spectral fit. We build a two-temperature model which does fit both RGS and EPIC results and propose that the high-T component is from SN debris and the low from heated material in the H ii region. The high ratio of Fe emission to that from O requires the remnant to be the product of a Type Ia supernova and points to a deflagration–detonation origin. Weak X-ray emission from the N9 superbubble is detected and briefly discussed. The abundance of Ne in N9 material seems higher than average for the LMC in both the superbubble spectrum and the low-temperature component of the remnant RGS spectrum.

The existence of strange matter in compact stars may give rise to striking outcomes of the various physical phenomena. As an alternative to neutron stars, a new class of compact stars called strange stars should exist if the strange matter hypothesis is true. In this paper, we investigate the possible construction of strange stars in quark matter phases based on the MIT bag model. We consider scenarios in which strange stars have no crusts. Then we apply two types of equations of state to quantify the mass–radius diagram for static strange star models, performing the numerical calculation of the modified Tolman–Oppenheimer–Volkoff equations in the context of 4D Einstein–Gauss–Bonnet (EGB) gravity. It is worth noting that the GB term gives rise to a nontrivial contribution to the gravitational dynamics in the limit D → 4. However, the claim that the resulting theory is one of pure gravity has been cast in doubt on several grounds. Thus, we begin our discussion by showing the regularized 4D EGB theory has an equivalent action as the novel 4D EGB in a spherically symmetric spacetime. We also study the effects of coupling constant α on the physical properties of the constructed strange stars including the compactness and criterion of adiabatic stability. Finally, we compare our results to those obtained from standard general relativity.

Some subtle distinctions between optically thin emission and optically thick emission (with a dynamically passive source of opacity) from an emitting surface are drawn. It is noted that photons may escape a region of high optical depth by dragging the opaque material with them, and that optically thick emission can have a shorter scale of variation than optically thin emission and less light echoing.

We report strong linear correlation between shifted velocity and line width of the broad blueshifted [O iii] components in Sloan Digital Sky Survey (SDSS) quasars. Broad blueshifted [O iii] components are commonly treated as indicators of outflows related to a central engine; however, it is still an open question whether the outflows are related to central accretion properties or related to local physical properties of narrow emission-line regions (NLRs). Here, the reported strong linear correlation with Spearman rank correlation coefficient 0.75 can be expected under the assumption of active galactic nuclei (AGNs) feedback-driven outflows, through a large sample of 535 SDSS quasars with reliable blueshifted broad [O iii] components. Moreover, there are very different detection rates for broad blueshifted and broad redshifted [O iii] components in quasars, and no positive correlation can be found between shifted velocity and line width of the broad redshifted [O iii] components, which provides further and strong evidence to reject the possibility of local outflows in NLRs leading to the broad blueshifted [O iii] components in quasars. Thus, the strong linear correlation can be treated as strong evidence for the broad blueshifted [O iii] components being better indicators of outflows related to central engine in AGNs. Furthermore, rather than central black hole masses, Eddington ratios and continuum luminosities have key roles in the properties of the broad blueshifted [O iii] components in quasars.

The inverse first ionization potential (FIP) effect, the depletion in the coronal abundance of elements like Fe, Mg, and Si that are ionized in the solar chromosphere relative to those that are neutral, has been identified in several solar flares. We give a more detailed discussion of the mechanism of fractionation by the ponderomotive force associated with magnetohydrodynamic waves, paying special attention to the conditions in which inverse-FIP fractionation arises in order to better understand its relation to the usual FIP effect, i.e., the enhancement of the coronal abundance of Fe, Mg, Si, etc. The FIP effect is generated by parallel propagating Alfvén waves, with either photospheric, or more likely coronal, origins. The inverse-FIP effect arises as upward-propagating fast-mode waves with an origin in the photosphere or below refract back downwards in the chromosphere where the Alfvén speed is increasing with altitude. We give a more physically motivated picture of the FIP fractionation, based on the wave refraction around inhomogeneities in the solar atmosphere, and inspired by previous discussions of analogous phenomena in the optical trapping of particles by laser beams. We apply these insights to modeling the fractionation and find good agreement with the observations of Katsuda et al. and Dennis et al.

The changes of broad emission lines should be a crucial issue in understanding the physical properties of changing-look active galactic nuclei (CL-AGNs). Here we present the results of an intensive and homogeneous 6 month long reverberation mapping (RM) monitoring campaign during a low-activity state of the CL-AGN Seyfert galaxy NGC 3516. Photometric and spectroscopic monitoring was carried out during 2018–2019 with the Lijiang 2.4 m telescope. The sampling is 2 days in most nights, and the average sampling is ∼3 days. The rest-frame time lags of Hα and Hβ are ${\tau }_{{\rm{H}}\alpha }={7.56}_{-2.10}^{+4.42}$ and ${\tau }_{{\rm{H}}\beta }={7.50}_{-0.77}^{+2.05}$ days, respectively. From an rms Hβ line dispersion of σ_line = 1713.3 ± 46.7 km s⁻¹ and a virial factor of f_σ = 5.5, the central black hole mass of NGC 3516 is estimated to be ${M}_{\mathrm{BH}}={2.4}_{-0.3}^{+0.7}\times {10}^{7}{M}_{\odot }$, which is in agreement with previous estimates. The velocity-resolved delays show that the time lags increase toward negative velocity for both Hα and Hβ. The velocity-resolved RM of Hα is done for the first time. These RM results are consistent with other observations before the spectral-type change, indicating a basically constant broad-line region structure during the CL process. The CL model of changes of accretion rate seems to be favored by long-term Hβ variability and RM observations of NGC 3516.

Ultra-diffuse galaxies have generated significant interest due to their large optical extents and low optical surface brightnesses, which challenge galaxy formation models. Here we present resolved synthesis observations of 12 H i-bearing ultra-diffuse galaxies (HUDs) from the Karl G. Jansky Very Large Array, as well as deep optical imaging from the WIYN 3.5 m telescope at Kitt Peak National Observatory. We present the data processing and images, including total intensity H i maps and H i velocity fields. The HUDs show ordered gas distributions and evidence of rotation, important prerequisites for the detailed kinematic models of Mancera Piña et al. We compare the H i and stellar alignment and extent, and find that H i extends beyond the already extended stellar component and the H i disk is often misaligned with respect to the stellar one, emphasizing the importance of caution when approaching inclination measurements for these extreme sources. We explore the H i mass–diameter scaling relation, and find that, although the HUDs have diffuse stellar populations, they fall along the relation with typical global H i surface densities. This resolved sample forms an important basis for more detailed study of the H i distribution in this extreme extragalactic population.

The cusp–core problem is one of the main challenges of the cold dark matter paradigm on small scales; the density of a dark matter halo is predicted to rise rapidly toward the center as ρ(r) ∝ r^α with α between −1 and −1.5, while such a cuspy profile has not been clearly observed. We have carried out the spatially resolved mapping of gas dynamics toward a nearby ultradiffuse galaxy (UDG), AGC 242019. The derived rotation curve of dark matter is well fitted by the cuspy profile as described by the Navarro–Frenk–White model, while the cored profiles including both the pseudo-isothermal and Burkert models are excluded. The halo has α = −(0.90 ± 0.08) at the innermost radius of 0.67 kpc, M_halo = (3.5 ± 1.2) × 10¹⁰M_⊙, and a small concentration of 2.0 ± 0.36. The UDG AGC 242019 challenges alternatives of cold dark matter by constraining the particle mass of fuzzy dark matter to be <0.11 × 10⁻²² or >3.3 × 10⁻²² eV, the cross section of self-interacting dark matter to be <1.63 cm² g⁻¹, and the particle mass of warm dark matter to be >0.23 keV, all of which are in tension with other constraints. The modified Newtonian dynamics is also inconsistent with a shallow radial acceleration relationship of AGC 242019. For the feedback scenario that transforms a cusp to a core, AGC 242019 disagrees with the stellar-to-halo mass ratio dependent model but agrees with the star formation threshold dependent model. As a UDG, AGC 242019 is in a dwarf-sized halo with weak stellar feedback, late formation time, normal baryonic spin, and low star formation efficiency (SFR/gas).

Neutron star mergers (NSMs) are promising astrophysical sites for the rapid neutron-capture ("r") process, but can their integrated yields explain the majority of heavy-element material in the Galaxy? One method to address this question implements a forward approach that propagates NSM rates and yields along with stellar formation rates and compares those results with observed chemical abundances of r-process-rich, metal-poor stars. In this work, we take the inverse approach by utilizing r-process-element abundance ratios of metal-poor stars as input to reconstruct the properties—especially the masses—of their neutron star (NS) binary progenitors. This novel analysis provides an independent avenue for studying the population of the original NS binary systems that merged and produced the r-process material now incorporated in Galactic metal-poor halo stars. We use ratios of elements typically associated with the limited-r-process and the actinide region to those in the lanthanide region (i.e., Zr/Dy and Th/Dy) to probe the NS masses of the progenitor merger. We find that NSMs can account for all r-process material in metal-poor stars that display r-process signatures, while simultaneously reproducing the present-day distribution of double-NS systems. Notably, with our model assumptions and the studied stellar sample, we postulate that the most r-process enhanced stars (the r–II stars) on their own would require progenitor NSMs of asymmetric systems that are distinctly different from present ones in the Galaxy. We also explore variations to the model and find that the predicted degree of asymmetry is most sensitive to the electron fraction of the remnant disk wind.

In a previous paper, second- and fourth-order explicit symplectic integrators were designed for a Hamiltonian of the Schwarzschild black hole. Following this work, we continue to trace the possibility of construction of explicit symplectic integrators for a Hamiltonian of charged particles moving around a Reissner–Nordström black hole with an external magnetic field. Such explicit symplectic methods are still available when the Hamiltonian is separated into five independently integrable parts with analytical solutions as explicit functions of proper time. Numerical tests show that the proposed algorithms share desirable properties in their long-term stability, precision, and efficiency for appropriate choices of step size. For the applicability of one of the new algorithms, the effects of black hole's charge, the Coulomb part of the electromagnetic potential and the magnetic parameter on the dynamical behavior are surveyed. Under some circumstances, the extent of chaos becomes strong with an increase of the magnetic parameter from a global phase-space structure. No variation of the black hole's charge other than the Coulomb part affects the regular and chaotic dynamics of the particles' orbits. A positive Coulomb part more easily induces chaos than a negative one.

How and when did galaxies form and assemble their stars and stellar mass? The answer to these questions, so crucial to astrophysics and cosmology, requires the full reconstruction of the so-called cosmic star formation rate density (SFRD), i.e., the evolution of the average star formation rate per unit volume of the universe. While the SFRD has been reliably traced back to 10–11 billion years ago, its evolution is still poorly constrained at earlier cosmic epochs, and its estimate is mainly based on galaxies luminous in the ultraviolet and with low obscuration by dust. This limited knowledge is largely due to the lack of an unbiased census of all types of star-forming galaxies in the early universe. We present a new approach to finding dust-obscured star-forming galaxies based on their emission at radio wavelengths coupled with the lack of optical counterparts. Here, we present a sample of 197 galaxies selected with this method. These systems were missed by previous surveys at optical and near-infrared wavelengths, and 22 of them are at very high redshift (i.e., z > 4.5). The contribution of these elusive systems to the SFRD is substantial and can be as high as 40% of the previously known SFRD based on UV-luminous galaxies. The mere existence of such heavily obscured galaxies in the first two billion years after the Big Bang opens new avenues to investigate the early phases of galaxy formation and evolution, and to understand the links between these systems and the massive galaxies that ceased their star formation at later cosmic times.

We present a study of 28 Type I superluminous supernovae (SLSNe) in the context of the ejecta mass and photospheric velocity. We combine photometry and spectroscopy to infer ejecta masses via the formalism of radiation diffusion equations. We present an improved method to determine the photospheric velocity by combining spectrum modeling and cross-correlation techniques. We find that Type I SLSNe can be divided into two groups according to their pre-maximum spectra. Members of the first group have a W-shaped absorption trough in their pre-maximum spectrum, usually identified as due to O ii. This feature is absent in the spectra of supernovae in the second group, whose spectra are similar to that of SN 2015bn. We confirm that the pre- or near-maximum photospheric velocities correlate with the velocity gradients: faster evolving SLSNe have larger photospheric velocities around maximum. We classify the studied SLSNe into the Fast or the Slow evolving group according to their estimated photospheric velocities, and find that all those objects that resemble SN 2015bn belong to the Slow evolving class, while SLSNe showing the W-like absorption are represented in both Fast and Slow evolving groups. We estimate the ejecta masses of all objects in our sample, and obtain values in the range 2.9 (±0.8)−208 (±61) M_⊙, with a mean of 43 (±12) M_⊙. We conclude that Slow evolving SLSNe tend to have higher ejecta masses compared to the Fast SLSNe. Our ejecta mass calculations suggests that SLSNe are caused by energetic explosions of very massive stars, irrespective of the powering mechanism of the light curve.

The nature of shock waves in nonfundamental mode RR Lyrae stars remains a mystery because of limited spectroscopic observations. We apply a pattern recognition algorithm on spectroscopic data from SDSS and LAMOST and report the first evidence of hydrogen emission in first-overtone (RRc) and multimode (RRd) RR Lyrae stars showing the "first apparition," which is the most prominent observational characteristic of shock in RR Lyrae variables. We find 10 RRc stars in SDSS, 10 RRc stars in LAMOST, and 3 RRd stars in LAMOST that show blueshifted Balmer emissions. The emission features possibly indicate the existence of shock waves. We calculate the radial velocities of the emission lines, which are related to the physical conditions occurring in the radiative zone of shock waves. Using photometric observations from ZTF, we present a detailed light-curve analysis for the frequency components in one of our RRd stars with hydrogen emission, RRdl3, for possible modulations. With the enormous volume of upcoming spectral observations of variable stars, our study raises the possibility of connecting the unexplained Blazhko effect to shock waves in nonfundamental mode RR Lyrae stars.

The use of Type Ia supernovae (SNe Ia) as cosmological tools has motivated significant effort to understand what drives the intrinsic scatter of SN Ia distance modulus residuals after standardization, characterize the distribution of SN Ia colors, and explain why properties of the host galaxies of the SNe correlate with SN Ia distance modulus residuals. We use a compiled sample of ∼1450 spectroscopically confirmed photometric light curves of SNe Ia and propose a solution to these three problems simultaneously that also explains an empirical 11σ detection of the dependence of Hubble residual scatter on SN Ia color. We introduce a physical model of color where intrinsic SN Ia colors with a relatively weak correlation with luminosity are combined with extrinsic dust-like colors (E(B − V)) with a wide range of extinction parameter values (R_V). This model captures the observed trends of Hubble residual scatter and indicates that the dominant component of SN Ia intrinsic scatter is variation in R_V. We also find that the recovered E(B − V) and R_V distributions differ based on global host-galaxy stellar mass, and this explains the observed correlation (γ) between mass and Hubble residuals seen in past analyses, as well as an observed 4.5σ dependence of γ on SN Ia color. This finding removes any need to ascribe different intrinsic luminosities to different progenitor systems. Finally, we measure biases in the equation of state of dark energy (w) up to ∣Δw∣ = 0.04 by replacing previous models of SN color with our dust-based model; this bias is larger than any systematic uncertainty in previous SN Ia cosmological analyses.

We have conducted a search for new strong gravitational lensing systems in the Dark Energy Spectroscopic Instrument Legacy Imaging Surveys' Data Release 8. We use deep residual neural networks, building on previous work presented by Huang et al. These surveys together cover approximately one-third of the sky visible from the Northern Hemisphere, reaching a z-band AB magnitude of ∼22.5. We compile a training sample that consists of known lensing systems as well as non-lenses in the Legacy Surveys and the Dark Energy Survey. After applying our trained neural networks to the survey data, we visually inspect and rank images with probabilities above a threshold. Here we present 1210 new strong lens candidates.

Type Ia supernovae (SNe Ia) are standardizable candles, but for over a decade there has been a debate on how to properly account for their correlations with host galaxy properties. Using the Bayesian hierarchical model UNITY, we simultaneously fit for the SN Ia light curve and host galaxy standardization parameters on a set of 103 Sloan Digital Sky Survey II SNe Ia. We investigate the influences of host stellar mass, along with both localized (r <3 kpc) and host-integrated average stellar ages, derived from stellar population synthesis modeling. We find that the standardization for the light-curve shape (α) is correlated with host galaxy standardization terms (γ_i) requiring simultaneous fitting. In addition, we find that these correlations themselves are dependent on host galaxy stellar mass that includes a shift in the color term (β) of 0.8 mag, only significant at 1.2σ due to the small sample. We find a linear host mass standardization term at the 3.7σ level, that by itself does not significantly improve the precision of an individual SN Ia distance. However, a standardization that uses both stellar mass and average local stellar age is found to be significant at >3σ in the two-dimensional posterior space. In addition, the unexplained scatter of SNe Ia absolute magnitude post standardization, is reduced from ${0.122}_{-0.018}^{+0.019}$ to 0.109 ± 0.017 mag, or ∼10%. We do not see similar improvements when using global ages. This combination is consistent with either metallicity or line-of-sight dust affecting the observed luminosity of SNe Ia.

The Maunder Minimum (MM; 1645–1715) is currently considered the only grand minimum within telescopic sunspot observations since 1610. During this epoch, the Sun was extremely quiet and unusually free from sunspots. However, despite a reduced frequency, candidate aurorae were reported in the mid-European sector during this period and have been associated with occurrences of interplanetary coronal mass ejections (ICMEs), although some of them have been identified as misinterpretations. Here, we have analyzed reports of candidate aurorae on 1680 June 1 with simultaneous observations in central Europe, and compared their descriptions with visual accounts of early modern aurorae. Contemporary sunspot drawings on 1680 May 22, 24, and 27 have shown a sunspot. This sunspot may have been a source of ICMEs, which caused the reported candidate aurorae. On the other hand, its intensity estimate shows that the geomagnetic storm during this candidate aurora was probably within the capability of the storms derived from the corotating interaction region (CIR). Therefore, we accommodate both ICMEs and CIRs as its possible origin. This interpretation is probably applicable to a number of candidate aurorae in the oft-cited Hungarian catalog, on the basis of the reconstructed margin of their equatorward auroral boundary. Moreover, this catalog itself has clarified that the considerable candidates during the MM were probably misinterpretations. Therefore, the frequency of the auroral visibility in Hungary was probably lower than previously considered and agrees more with the generally slow solar wind in the existing reconstructions, whereas sporadic occurrences of sunspots and coronal holes still caused occasional geomagnetic storms.

We present StrayCats, a catalog of NuSTAR stray light observations of X-ray sources. Stray light observations arise for sources 1°–4° away from the telescope pointing direction. At this off-axis angle, X-rays pass through a gap between the optics and aperture stop and so do not interact with the X-ray optics; instead, they directly illuminate the NuSTAR focal plane. We have systematically identified and examined over 1400 potential observations resulting in a catalog of 436 telescope fields and 78 stray light sources that have been identified. The sources identified include historically known persistently bright X-ray sources, X-ray binaries in outburst, pulsars, and type I X-ray bursters. In this paper, we present an overview of the catalog, how we identified the StrayCats sources, and the analysis techniques required to produce high-level science products. Finally, we present a few brief examples of the science quality of these unique data.

A protoplanetary disk (PPD) typically forms a dead zone near its midplane at a distance of a few astronomical units from the central protostar. Accretion through such a magnetically layered disk can be intrinsically unstable and has been associated with episodic outbursts in young stellar objects. We present the first investigation into the effects of a low-metallicity environment on the structure of the dead zone, as well as the resulting outbursting behavior of the PPD. We conducted global numerical hydrodynamic simulations of PPD formation and evolution in the thin-disk limit. The consequences of metallicity were considered via its effects on the gas and dust opacity of the disk, the thickness of the magnetically active surface layer, and the temperature of the prestellar cloud core. We show that the metal-poor disks accumulate much more mass in the innermost regions as compared to the solar-metallicity counterparts. The duration of the outbursting phase also varies with metallicity; the low-metallicity disks showed more powerful luminosity eruptions with a shorter burst phase, which was confined mostly to the early, embedded stages of the disk evolution. The lowest-metallicity disks with the higher cloud core temperature showed the most significant differences. The occurrence of outbursts was relatively rare in the disks around low-mass stars, and this was especially true at the lowest metallicities. We conclude that the metal content of the disk environment can have profound effects on both the disk structure and evolution in terms of episodic accretion.

Solar filaments often erupt partially. Although how they split remains elusive, the splitting process has the potential of revealing the filament structure and eruption mechanism. Here we investigate the pre-eruption splitting of an apparently single filament and its subsequent partial eruption on 2012 September 27. The evolution is characterized by three stages with distinct dynamics. During the quasi-static stage, the splitting proceeds gradually for about 1.5 hr, with the upper branch rising at a few kilometers per second and displaying swirling motions about its axis. During the precursor stage that lasts for about 10 minutes, the upper branch rises at tens of kilometers per second, with a pair of conjugated dimming regions starting to develop at its footpoints; with the swirling motions turning chaotic, the axis of the upper branch whips southward, which drives an arc-shaped extreme-ultraviolet front propagating in a similar direction. During the eruption stage, the upper branch erupts with the onset of a C3.7-class two-ribbon flare, while the lower branch remains stable. Judging from the well-separated footpoints of the upper branch from those of the lower one, we suggest that the pre-eruption filament processes a double-decker structure composed of two distinct flux bundles, whose formation is associated with gradual magnetic flux cancellations and converging photospheric flows around the polarity inversion line.

The search for astronomical pulsed signals within noisy data in the radio band is usually performed through an initial Fourier analysis to find "candidate" frequencies and then refined through the folding of the time series using trial frequencies close to the candidate. In order to establish the significance of the pulsed profiles found at these trial frequencies, pulsed profiles are evaluated with a χ² test to establish how much they depart from a null hypothesis where the signal is consistent with a flat distribution of noisy measurements. In high-energy astronomy, the χ² statistic has widely been replaced by the ${Z}_{n}^{2}$ statistic and H-test, as they are more sensitive to extra information, such as the harmonic content of the pulsed profile. The ${Z}_{n}^{2}$ statistic and H-test were originally developed for use with "event data" composed of arrival times of single photons, leaving it unclear how these methods could be used in radio astronomy. In this paper, we present a version of the ${Z}_{n}^{2}$ statistic and H-test for pulse profiles with Gaussian uncertainties appropriate for radio or even optical pulse profiles. We show how these statistical indicators provide better sensitivity to low-significance pulsar candidates with respect to the usual χ² method and a straightforward way to discriminate between pulse profile shapes. Moreover, they provide an additional tool for radio frequency interference rejection.

Recent observations revealed a coherence between the spin vector of a galaxy and the orbital motion of its neighbors. We refer to the phenomenon as "the spin–orbit alignment (SOA)" and explore its physical origin via the IllustrisTNG simulation. This is the first study to utilize a cosmological hydrodynamic simulation to investigate the SOA of galaxy pairs. In particular, we identify paired galaxies at z = 0 having the nearest neighbor with mass ratios from 1/10 to 10 and calculate the spin–orbit angle for each pair. Our results are as follows. (a) There exists a clear preference for prograde orientations (i.e., SOA) for galaxy pairs, qualitatively consistent with observations. (b) The SOA is significant for both baryonic and dark matter spins, being the strongest for gas and the weakest for dark matter. (c) The SOA is stronger for less massive targets and for targets having closer neighbors. (d) The SOA strengthens for galaxies in low-density regions, and the signal is dominated by central–satellite pairs in low-mass halos. (e) There is an explicit dependence of the SOA on the duration of interaction with its current neighbor. Taken together, we propose that the SOA witnessed at z = 0 has been developed mainly by interactions with a neighbor for an extended period of time, rather than tidal torque from the ambient large-scale structure.

We analyze the evolution of shock waves in high-resolution 3D radiative MHD simulations of the quiet Sun and their synthetic emission characteristics. The simulations model the dynamics of a 12.8 × 12.8 × 15.2 Mm quiet-Sun region (including a 5.2 Mm layer of the upper convection zone and a 10 Mm atmosphere from the photosphere to corona) with an initially uniform vertical magnetic field of 10 G, naturally driven by convective flows. We synthesize the Mg II and C II spectral lines observed by the Interface Region Imaging Spectrograph (IRIS) satellite and extreme ultraviolet emission observed by the Solar Dynamics Observatory (SDO)/AIA telescope. Synthetic observations are obtained using the RH1.5D radiative transfer code and temperature response functions at both the numerical and instrumental resolutions. We found that the Doppler velocity jumps of the C II 1334.5 Å IRIS line and a relative enhancement of the emission in the 335 Å SDO/AIA channel are the best proxies for the enthalpy deposited by shock waves into the corona (with Kendall's τ correlation coefficients of 0.59 and 0.38, respectively). The synthetic emission of the lines and the extreme ultraviolet passbands are correlated with each other during the shock-wave propagation. All studied shocks are mostly hydrodynamic (i.e., the magnetic energy carried by horizontal fields is ≤2.6% of the enthalpy for all events) and have Mach numbers >1.0–1.2 in the low corona. The study reveals the possibility of diagnosing energy transport by shock waves into the solar corona, as well as their other properties, by using IRIS and SDO/AIA sensing observations.

The fast multipole method (FMM) obeys periodic boundary conditions "natively" if it uses a periodic Green's function for computing the multipole expansion in the interaction zone of each FMM oct-tree node. One can define the "optimal" Green's function for such a method that results in the numerical solution that converges to the equivalent particle-mesh (PM) solution in the limit of sufficiently high order of multipoles. A discrete functional equation for the optimal Green's function can be derived, but is not practically useful as methods for its solution are not known. Instead, this paper presents an approximation for the optimal Green's function that is accurate to better than 10⁻³ in ${L}_{\mathrm{MAX}}$ norm and 10⁻⁴ in L₂ norm for practically useful multipole counts. Such an approximately optimal Green's function offers a practical way for implementing the FMM with periodic boundary conditions natively, without the need to compute lattice sums or to rely on hybrid FMM-PM approaches.

Without an existing large-scale coherent magnetic field in the early universe, Population III stars would likely rotate at or near breakup speed. In this work, focusing on the accretion phase of Population III stars, we investigate the possibility of generating a coherent magnetic field through large-scale dynamo processes, as well as the corresponding field saturation level. Using results from hydrodynamic simulations performed with a cylindrical grid, we demonstrate that primordial accretion disks are turbulent with a Shakura–Sunyaev disk parameter α_ss ≳ 10⁻³ and evidence for helical turbulence with a dynamo number ∣D_αΩ∣ ≫ 10. The presence of helical turbulence at these levels allows large-scale dynamo modes to grow, and the saturation level is determined by the amount of net helicity remaining in the dynamo active regions (i.e., the quenching problem). We demonstrate that if the accretion could successfully alleviate the quenching problem, the magnetic field can reach approximate equipartition with B/B_eq ∼ 3.

We present version 10 of the CHIANTI package. In this release, we provide updated atomic models for several helium-like ions and for all the ions of the beryllium, carbon, and magnesium isoelectronic sequences that are abundant in astrophysical plasmas. We include rates from large-scale atomic structure and scattering calculations that are in many cases a significant improvement over the previous version, especially for the Be-like sequence, which has useful line diagnostics to measure the electron density and temperature. We have also added new ions and updated several of them with new atomic rates and line identifications. Also, we have added several improvements to the IDL software, to speed up the calculations and to estimate the suppression of dielectronic recombination.

We report the first results of a systematic investigation to characterize blazar variability power spectral densities (PSDs) at optical frequencies using densely sampled (5–15 minutes of integration time), high photometric accuracy (≲0.2%–0.5%) R-band intranight light curves, covering timescales ranging from several hours to ∼15 minutes. Our sample consists of 14 optically bright blazars—nine BL Lacertae objects and five flat-spectrum radio quasars (FSRQs)—which have shown statistically significant variability during 29 monitoring sessions. We model the intranight PSDs as simple power laws and derive the best-fit slope along with the uncertainty using the "power spectral response" method. Our main results are as follows: (1) in 19 out of 29 monitoring sessions, the intranight PSDs show an acceptable fit to simple power laws at a rejection confidence ≤90%; (2) for these 19 instances, the PSD slopes show a wide range of 1.4 to 4.0, consistent with the statistical characters of red-noise (slope ∼ 2) and black-noise (slope ≥ 3) stochastic processes; (3) the average PSD slopes for the BL Lac objects and FSRQs are indistinguishable from one another; and (4) the normalization of intranight PSDs for individual blazar sources monitored on more than one occasion turns out to be consistent with one another with a few exceptions. The average PSD slope, 2.9 ± 0.3 (1σ uncertainty), is steeper than that of red noise–type variability found on longer timescales (many decades to days), indicative of a cutoff in the variability spectrum on timescales around a few days at the synchrotron frequencies of the emission spectrum.

The composition of giant planets is imprinted by their migration history and the compositional structure of their hosting disks. Studies in recent literature have investigated how the abundances of C and O can constrain the formation pathways of giant planets forming within few tens of au from a star. New ALMA observations, however, suggest planet-forming regions possibly extending to hundreds of au. We explore the implications of these wider formation environments through n-body simulations of growing and migrating giant planets embedded in planetesimal disks, coupled with a compositional model of the protoplanetary disk where volatiles are inherited from the molecular cloud and refractories are calibrated against extrasolar and Solar System data. We find that the C/O ratio provides limited insight on the formation pathways of giant planets that undergo large-scale migration. This limitation can be overcome, however, thanks to nitrogen and sulfur. Jointly using the C/N, N/O, and C/O ratios breaks any degeneracy in the formation and migration tracks of giant planets. The use of elemental ratios normalized to the respective stellar ratios supplies additional information on the nature of giant planets, thanks to the relative volatility of O, C, and N in disks. When the planetary metallicity is dominated by the accretion of solids C/N* > C/O* > N/O* (* denoting this normalized scale), otherwise N/O* > C/O* > C/N*. The S/N ratio provides an additional independent probe into the metallicity of giant planets and their accretion of solids.

GRS 1915+105 is a stellar-mass black hole that is well known for exhibiting at least 12 distinct classes of X-ray variability and correlated multi-wavelength behavior. Despite such extraordinary variability, GRS 1915+105 remained one of the brightest sources in the X-ray sky. However, in early 2019, the source became much fainter, apparently entering a new accretion state. Here, we report the results of an extensive, year-long monitoring campaign of GRS 1915+105 with the Neil Gehrels Swift Observatory. During this interval, the flux of GRS 1915+105 gradually diminished; the observed count rate eventually dropped by two orders of magnitude. Simple but robust spectral fits to these monitoring observations show that this new state results from the combination of a dramatic and persistent increase in internal obscuration, and a reduced mass accretion rate. The internal obscuration is the dominant effect, with a median value of N_H = 7 × 10²³ cm⁻². In a number of observations, the source appears to be Compton-thick. We suggest that this state should be identified as the "obscured state," and discuss the implications of this new (or rarely observed) accretion mode for black holes across the mass scale.

Energetic particles spectra at interplanetary shocks often exhibit a power law within a narrow momentum range softening at higher energy. We introduce a transport equation accounting for particle acceleration and escape with diffusion contributed by self-generated turbulence close to the shock and by preexisting turbulence far upstream. The upstream particle intensity steepens within one diffusion length from the shock as compared with diffusive shock acceleration rollover. The momentum spectrum, controlled by macroscopic parameters such as shock compression, speed, far-upstream diffusion coefficient, and escape time at the shock, can be reduced to a log-parabola and also to a broken power law. In the case of upstream uniform diffusion coefficient, the largely used power-law/exponential cutoff solution is retrieved.

This paper studies the energy dissipation of nonthermal electrons in the chromospheric flare ribbons during the peak time of a Geostationary Operational Environmental Satellite X-class flare (SOL2011-09-06) using desaturated Solar Dynamics Observatory/Atmospheric Imaging Assembly extreme-ultraviolet (EUV) narrow-band images. The temperature distribution in emission measure, called the differential emission measure (DEM), derived from the EUV fluxes from the flare ribbons shows an increase in the emission measure up to a temperature around 9 × 10⁶ K, followed by a steep decline at higher temperatures. In contrast, the flare loop reaches temperatures up to 27 × 10⁶ K. This result is in agreement with previously reported single-temperature measurements using soft X-ray filter images, as well as DEM distributions reported for smaller flares obtained from EUV line observations. The main difference between small and large flares appears to be an increased emission measure in the flare ribbons, while the ribbon peak temperature is similar for all flares. This is different from the flare loop temperatures, where the hottest temperatures occur in the largest flares. However, the physically relevant quantity for energy dissipation, the energy content of the heated plasma as a function of temperature, does not need to peak at the same temperature as the DEM. The poorly constrained source thickness in radial extent of the flare ribbons has a significant impact on the shape of the differential thermal energy distribution. In particular, if the highest temperatures occur over a wide radial extent as "evaporating" plasma starts expending, the largest amount of energy could potentially be hidden above the peak temperature of the DEM.

Jets (fast collimated outflows) are claimed to be the main shaping agent of the most asymmetric planetary nebulae (PNs), as they impinge on the circumstellar material at late stages of the asymptotic giant branch phase. The first jet detected in a PN was that of NGC 2392, yet there is no available image because of its low surface brightness contrast with the bright nebular emission. Here we take advantage of the tomographic capabilities of Gran Telescopio de Canarias Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía high-dispersion integral field spectroscopic observations of the jet in NGC 2392 to gain unprecedented details of its morphology and kinematics. The jet of NGC 2392 is found to emanate from the central star, break through the walls of the inner shell of this iconic PN and extend outside the nebula's outermost regions with an S-shaped morphology suggestive of precession. At odds with the fossil jets found in mature PNs, the jet in NGC 2392 is currently being collimated and launched. The high nebular excitation of NGC 2392, which implies an He⁺⁺/He ionization fraction too high to be attributed to the known effective temperature of the star, has been proposed in the past to hint at the presence of a hot white dwarf companion. In conjunction with the hard X-ray emission from the central star, the present-day jet collimation would support the presence of such a double-degenerate system where one component undergoes accretion from a remnant circumbinary disk of the common envelope phase.

Magnetohydrodynamic (MHD) turbulence plays an important role for the fast energy release and wave structures related to coronal mass ejections (CMEs). The CME plasma has been observed to be strongly heated during solar eruptions, but the heating mechanism is not understood. In this paper, we focus on the hot, dense region at the bottom of the CME and the generation of coronal wave trains therein using a high-resolution 2.5D MHD simulation. Our results show that the interaction between the tearing current sheet and the turbulence, including the termination shocks (TSs) at the bottom of the CME, can make a significant contribution to heating the CME, and the heating rate in this region is found to be greater than the kinetic energy transfer rate. Also, the turbulence can be somewhat amplified by the TSs. The compression ratio of the TS under the CME can exceed 4 due to thermal conduction, but such a strong TS is hardly detectable in all Solar Dynamics Observatory/Atmospheric Imaging Assembly bands. And turbulence is an indispensable source for the periodic generation of coronal wave trains around the CME.

Supernova remnant RX J1713.7-3946 has exhibited the largest surface brightness and a detailed spectral and shell-type morphology, and is one of the brightest TeV sources. The recent H.E.S.S. observation of RX J1713.7-3946 revealed a broken power-law GeV–TeV gamma-ray and a more extended gamma-ray spatial radial profile than in the X-ray band. Based on the diffusion shock acceleration model, we solve spherically symmetric hydrodynamic equations and particle transport equations, and investigate the multi-band non-thermal emission of RX J1713.7-3946 and radial profiles of its surface brightness for two selected zones in the leptonic scenario for gamma-ray emission. We found (1) the diffusion coefficient has a weak energy dependence, and the Kolmogorov type is favored; (2) the magnetic field strength can vary linearly or nonlinearly with radius for different surrounding environments because of possible turbulence in the shock downstream region, and compressional amplification is likely to exist at the shock front; (3) the non-thermal photons from radio to X-ray bands are dominated by synchrotron emission from relativistic electrons if the GeV–TeV gamma-rays are produced by inverse Compton scattering from these electrons interacting with the background photons; then the X-ray and gamma-ray radial profiles can be reproduced except for the more extended gamma-ray emission.

Motivated by the observations and linear theory analysis of ionospheric irregularities at Mars, we performed numerical simulations of the nonlinear evolution of the electromagnetic gradient drift instability in the Martian ionospheric dynamo region. The seeding source of ionospheric irregularities is perturbation zonal neutral wind. We found that the perturbation electric fields induced by the gradient drift instability can convect lower density plasma into higher density plasma at higher altitudes. Then, the associated perturbation magnetic field and electric field can cause the velocity shear of the plasma, which induced the Kelvin–Helmholtz instability at higher altitude. The Kelvin–Helmholtz instabilities furthermore lead to smaller-scale irregularities in plasma density, magnetic field, and electric field in the Martial ionosphere. Key points: (1) Nonlinear simulation of small-scale ionospheric irregularities at Mars was present. (2) Ionospheric irregularities at Mars can be seeded by the perturbation neutral winds. (3) Model results are comparable to linear theory analysis and satellite observations.

The second Gaia data release (DR2) delivers accurate and homogeneous photometry data of the whole sky of an exquisite quality, reaching down to the unprecedented millimagnitude (mmag) level for the G, G_RP, and G_BP passbands. However, the presence of magnitude-dependent systematic effects at the 10 mmag level limits its power in scientific exploitation. In this work, using about a half million stars in common with the LAMOST DR5, we apply the spectroscopy-based stellar color regression method to calibrate the Gaia G − G_RP and G_BP − G_RP colors. With an unprecedented precision of about 1 mmag, systematic trends with G magnitude are revealed for both colors in great detail, reflecting changes in instrument configurations. Color-dependent trends are found for the G_BP − G_RP color and for stars brighter than G ∼ 11.5 mag. The maximum correction term of the calibration is about 20 mmag in general and varies by a few mmag/mag. A revised color–color diagram of Gaia DR2 is given, and some applications are briefly discussed.

Luminous compact blue galaxies (LCBGs) are compact, star-forming galaxies that are rarely observed in the local universe but abundant at z = 1. This increase in LCBG number density over cosmic lookback time roughly follows the increase in the star formation rate density of the universe over the same period. We use publicly available data in the COSMOS field to study the evolution of the largest homogeneous sample of LCBGs to date by deriving their luminosity function in four redshift bins over the range 0.1 ≤ z ≤ 1. We find that over this redshift range, the characteristic luminosity (M*) increases by ∼0.2 mag, and the number density increases by a factor of 4. While LCBGs make up only about 18% of galaxies more luminous than M_B = −18.5 at z ∼ 0.2, they constitute roughly 54% at z ∼ 0.9. The strong evolution in number density indicates that LCBGs are an important population of galaxies to study in order to better understand the decrease in the star formation rate density of the universe since z ∼ 1.

We report on the temporal properties of the ultraluminous X-ray (ULX) pulsar M51 ULX-7 inferred from the analysis of the 2018–2020 Swift/X-ray Telescope monitoring data and archival Chandra data obtained over a period of 33 days in 2012. We find an extended low flux state, which might be indicative of propeller transition, lending further support to the interpretation that the neutron star is rotating near equilibrium. Alternatively, this off-state could be related to a variable superorbital period. Moreover, we report the discovery of periodic dips in the X-ray light curve that are associated with the binary orbital period. The presence of the dips implies a configuration where the orbital plane of the binary is closer to an edge-on orientation, and thus demonstrates that favorable geometries are not necessary in order to observe ULX pulsars. These characteristics are similar to those seen in prototypical X-ray pulsars such as Her X-1 and SMC X-1 or other ULX pulsars such as NGC 5907 ULX1.

Intensity mapping of the H i 21 cm line and the CO 2.61 mm line from the epoch of reionization has emerged as powerful, complementary, probes of the high-redshift universe. However, both maps and their cross-correlation are dominated by foregrounds. We propose a new analysis by which the signal is unbiased by foregrounds, i.e., it can be measured without foreground mitigation. We construct the antisymmetric part of two-point cross-correlation between intensity maps of the H i 21 cm line and the CO 2.61 mm line, arising because the statistical fluctuations of two fields have different evolution in time. We show that the sign of this new signal can distinguish model independently whether inside-out reionization happens during some interval of time. More importantly, within the framework of the excursion-set model of reionization, we demonstrate that the slope of the dipole of H i–CO cross-power spectrum at large scales is linear to the rate of change of global neutral fraction of hydrogen in a manner independent of reionization parameters, until the slope levels out near the end of reionization, but this trend might possibly depend on the framework of reionization modeling. The H i–CO dipole may be a smoking-gun probe for the speed of reionization, or "standard speedometer" for cosmic reionization. Observations of this new signal will unveil the global reionization history from the midpoint to near the completion of reionization.

Motivated by the discovery of the ultra-strong emission-line starburst galaxies (EELGs) known as "green pea galaxies," in this work we consider their contribution to the intergalactic flux of ionizing UV at high redshifts. Most galaxies that have been observed show a precipitous drop in the flux blueward of their Lyman limit. However, recent observations of EELGs have discovered that many more Lyman continuum photons escape from them into intergalactic space than previously suspected. We calculate their contribution to the extragalactic background light. We also calculate the effect of these photons on the absorption of high-energy γ-rays. For the more distant γ-ray sources, particularly at z ≥ 3, an intergalactic opacity above a few GeV is significantly higher than previous estimates which ignored the Lyman continuum photons. We calculate the results of this increased opacity on observed γ-ray spectra, which produce a high-energy turnover starting at lower energies than previously thought, and a gradual spectral steepening that may also be observable.

The estimation of spectroscopic and photometric redshifts (spec-z and photo-z) is crucial for future cosmological surveys. It can directly affect several powerful measurements of the universe, such as weak lensing and galaxy clustering. In this work, we explore the accuracies of spec-z and photo-z that can be obtained by the China Space Station Optical Surveys, which is a next-generation space survey, using a neural network. The one-dimensional Convolutional Neural Networks and Multi-Layer Perceptron (MLP, the simplest form of an artificial neural network) are employed to derive spec-z and photo-z, respectively. The mock spectral and photometric data used for training and testing the networks are generated based on the COSMOS catalog. The networks have been trained with noisy data by creating Gaussian random realizations to reduce the statistical effects, resulting in a similar redshift accuracy for data with both high and low signal-to-noise ratios. The probability distribution functions of the predicted redshifts are also derived via Gaussian random realizations of the testing data, and then the best-fit redshifts and 1σ errors also can be obtained. We find that our networks can provide excellent redshift estimates with accuracies of ∼0.001 and 0.01 on spec-z and photo-z, respectively. Compared to existing photo-z codes, our MLP has a similar accuracy but is more efficient in the training process. The fractions of catastrophic redshifts or outliers can be dramatically suppressed compared to the ordinary template-fitting method. This indicates that the neural network method is feasible and powerful for spec-z and photo-z estimations in future cosmological surveys.

A highly important aspect of solar activity is the coupling between eruptions and the surrounding coronal magnetic field topology, which determines the trajectory and morphology of the event and can even lead to sympathetic eruptions from multiple sources. In this paper, we report on a numerical simulation of a new type of coupled eruption, in which a coronal jet initiated by a large pseudostreamer filament eruption triggers a streamer-blowout coronal mass ejection (CME) from the neighboring helmet streamer. Our configuration has a large opposite-polarity region positioned between the polar coronal hole and a small equatorial coronal hole, forming a pseudostreamer flanked by the coronal holes and the helmet streamer. Further out, the pseudostreamer stalk takes the shape of an extended arc in the heliosphere. We energize the system by applying photospheric shear along a section of the polarity inversion line within the pseudostreamer. The resulting sheared-arcade filament channel develops a flux rope that eventually erupts as a classic coronal-hole-type jet. However, the enhanced breakout reconnection above the channel as the jet is launched progresses into the neighboring helmet streamer, partially launching the jet along closed helmet streamer field lines and blowing out the streamer top to produce a classic bubble-like CME. This CME is strongly deflected from the jet's initial trajectory and contains a mixture of open and closed magnetic field lines. We present the detailed dynamics of this new type of coupled eruption, its underlying mechanisms, and the implications of this work for the interpretation of in situ and remote-sensing observations.

Infrared observations probe the warm gas in the inner regions of planet-forming disks around young Sun-like T Tauri stars. In these systems, H₂O, OH, CO, CO₂, C₂H₂, and HCN have been widely observed. However, the potentially abundant carbon carrier CH₄ remains largely unconstrained. The James Webb Space Telescope (JWST) will be able to characterize mid-infrared fluxes of CH₄ along with several other carriers of carbon and oxygen. In anticipation of the JWST mission, we model the physical and chemical structure of a T Tauri disk to predict the abundances and mid-infrared fluxes of observable molecules. A range of compositional scenarios are explored involving the destruction of refractory carbon materials and alterations to the total elemental (volatile and refractory) C/O ratio. Photon-driven chemistry in the inner disk surface layers largely destroys the initial carbon and oxygen carriers. This causes models with the same physical structure and C/O ratio to have similar steady-state surface compositions, regardless of the initial chemical abundances. Initial disk compositions are better preserved in the shielded inner disk midplane. The degree of similarity between the surface and midplane compositions in the inner disk will depend on the characteristics of vertical mixing at these radii. Our modeled fluxes of observable molecules respond sensitively to changes in the disk gas temperature, inner radius, and total elemental C/O ratio. As a result, mid-infrared observations of disks will be useful probes of these fundamental disk parameters, including the C/O ratio, which can be compared to values determined for planetary atmospheres.

We study the carbon monoxide (CO) excitation, mean molecular gas density, and interstellar radiation field (ISRF) intensity in a comprehensive sample of 76 galaxies from local to high redshift (z ∼ 0–6), selected based on detections of their CO transitions J = 2 → 1 and 5 → 4 and their optical/infrared/(sub)millimeter spectral energy distributions (SEDs). We confirm the existence of a tight correlation between CO excitation as traced by the CO (5–4)/(2–1) line ratio R₅₂ and the mean ISRF intensity $\left\langle U\right\rangle$ as derived from infrared SED fitting using dust SED templates. By modeling the molecular gas density probability distribution function (PDF) in galaxies and predicting CO line ratios with large velocity gradient radiative transfer calculations, we present a framework linking global CO line ratios to the mean molecular hydrogen gas density $\left\langle {n}_{{{\rm{H}}}_{2}}\right\rangle$ and kinetic temperature T_kin. Mapping in this way observed R₅₂ ratios to $\left\langle {n}_{{{\rm{H}}}_{2}}\right\rangle$ and T_kin probability distributions, we obtain positive $\left\langle U\right\rangle$–$\left\langle {n}_{{{\rm{H}}}_{2}}\right\rangle$ and $\left\langle U\right\rangle$–T_kin correlations, which imply a scenario in which the ISRF in galaxies is mainly regulated by T_kin and (nonlinearly) by $\left\langle {n}_{{{\rm{H}}}_{2}}\right\rangle$. A small fraction of starburst galaxies showing enhanced $\left\langle {n}_{{{\rm{H}}}_{2}}\right\rangle$ could be due to merger-driven compaction. Our work demonstrates that ISRF and CO excitation are tightly coupled and that density–PDF modeling is a promising tool for probing detailed ISM properties inside galaxies.

Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) images the full solar disk in several extreme-ultraviolet (EUV) bands that are each sensitive to coronal plasma emissions of one or more specific temperatures. We observe that when isolated active regions (ARs) are on the disk, full-disk images in some of the coronal EUV channels show the outskirts of the AR as a dark moat surrounding the AR. Here we present seven specific examples, selected from time periods when there was only a single AR present on the disk. Visually, we observe the moat to be most prominent in the AIA 171 Å band, which has the most sensitivity to emission from plasma at log₁₀T = 5.8. By examining the 1D line-of-sight emission measure temperature distribution found from six AIA EUV channels, we find the intensity of the moat to be most depressed over the temperature range log₁₀T ≈ 5.7–6.2 for most of the cases. We argue that the dark moat exists because the pressure from the strong magnetic field that splays out from the AR presses down on underlying magnetic loops, flattening those loops—along with the lowest of the AR's own loops over the moat—to a low altitude. Those loops, which would normally emit the bulk of the 171 Å emission, are restricted to heights above the surface that are too low to have 171 Å emitting plasmas sustained in them, according to Antiochos & Noci, while hotter EUV-emitting plasmas are sustained in the overlying higher-altitude long AR-rooted coronal loops. This potentially explains the low-coronal-temperature dark moats surrounding the ARs.

The symmetry axes of active galactic nuclei (AGNs) are randomly distributed in space, but highly inclined sources are heavily obscured and are not seen as quasars with broad emission lines. The obscuring torus geometry determines the average viewing angle, and if the torus geometry changes with the redshift, this average viewing angle will also change. Thus, the ratio between the isotropic luminosity and observed luminosity may change systematically with redshift. Therefore, if we use quasars to measure the luminosity distance by evaluating the isotropic absolute luminosity and measuring the observed flux, we can have a redshift-dependent bias that can propagate to cosmological parameters. We propose a toy model for testing the effect of viewing angle uncertainty on the measurement of the luminosity distance. The model is based on analytical description of the obscuring torus applied to one-parameter observational data. It illustrates the possible change of the torus covering factor between the two chosen redshift ranges. We have estimated the possible errors in specific cosmological parameters (H₀, Ω_m) for the flat Lambda cold dark matter cosmology if a method is calibrated at low redshift and applied to the higher redshift. The errors in the cosmological parameters due to potential dependence of the viewing angle on redshift are found to be potentially significant, and the effect will have to be accommodated in the future in all quasar-based cosmological methods. A careful systematic study of AGNs means that a viewing angle across the redshift is necessary, with the use of appropriate samples and models that uniquely determine the inclination of each source.

The detection of almost 100% linearly polarized emission from the fast radio burst source FRB 121102 implies coherent emission of relativistic electrons moving perpendicular to the ambient magnetic field. The origin of such a particle distribution is very intriguing. Given that FRB 121102 is likely driven by a neutron star, we explored orbits of charged particles trapped in a dipole magnetic field (the Störmer problem). Most previous studies focused on particles with relatively low energies so that the guiding center approximation may be applied. High-energy particles usually have chaotic orbits except those on a periodic orbit or near stable periodic orbits. Via evaluation of the maximum Lyapunov exponent of orbits of particles launched from the equatorial plane with an axial velocity (the angular velocity sets the length and energy scales of the system), we found prominent regions of quasi-periodic orbits around stable periodic orbits in the equatorial plane at high energies. Particles in these orbits oscillate around the equatorial plane and their radial distance from the dipole can vary by a factor of ∼2. Relativistic electrons in such orbits may be responsible for the almost 100% polarized emission from FRB 121102.

We characterize in detail the two ∼0.3 pc long filamentary structures found within the subsonic region of Barnard 5. We use combined Robert C. Byrd Green Bank Telescope and Very Large Array observations of the molecular lines NH₃(1,1) and (2,2) at a resolution of 1800 au, as well as James Clerk Maxwell Telescope continuum observations at 850 and 450 μm at a resolution of 4400 and 3000 au, respectively. We find that both filaments are highly supercritical with a mean mass per unit length, M/L, of ∼80 M_⊙ pc⁻¹ after background subtraction, with local increases reaching values of ∼150 M_⊙ pc⁻¹. This would require a magnetic field strength of ∼500 μG to be stable against radial collapse. We extract equidistant cuts perpendicular to the spine of the filament and fit a modified Plummer profile as well as a Gaussian to each of the cuts. The filament widths (deconvolved FWHM) range between 6500 and 7000 au (∼0.03 pc) along the filaments. This equals ∼twice the radius of the flat inner region. We find an anticorrelation between the central density and this flattening radius, suggestive of contraction. Further, we also find a strong correlation between the power-law exponent at large radii and the flattening radius. We note that the measurements of these three parameters fall in a plane and derive their empirical relation. Our high-resolution observations provide direct constraints on the distribution of the dense gas within supercritical filaments showing pre- and protostellar activity.

Stellar ultraviolet (UV) radiation drives photochemistry, and extreme-ultraviolet (EUV) radiation drives mass loss in exoplanet atmospheres. However, the UV flux is partly unobservable due to interstellar absorption, particularly in the EUV range (100–912 Å). It is therefore necessary to reconstruct the unobservable spectra in order to characterize the radiation environment of exoplanets. In the present work, we use a radiative transfer code SSRPM to build one-dimensional semiempirical models of two M dwarf exoplanet hosts, GJ 832 and GJ 581, and synthesize their spectra. SSRPM is equipped with an extensive atomic and molecular database and full-NLTE capabilities. We use observations in the visible, ultraviolet, and X-ray ranges to constrain atmospheric structures of the modeled stars. The synthesized integrated EUV fluxes are found to be in good agreement with other reconstruction techniques, but the spectral energy distributions disagree significantly across the EUV range. More than two-thirds of the EUV flux is formed above 10⁵ K. We find that the far-ultraviolet (FUV) continuum contributes 42%–54% of the entire FUV flux between 1450 and 1700 Å. The comparison of stellar structures of GJ 832 and GJ 581 suggests that GJ 832 is a more magnetically active star, which is corroborated by other activity indicators.

Several publications highlight the importance of the observations of bow shocks to learn more about the surrounding interstellar medium and radiation field. We revisit the most prominent dusty and gaseous bow shock source, X7, close to the supermassive black hole, Sgr A*, using multiwavelength analysis. For the purpose of this study, we use Spectrograph for Integral Field Observations in the Near Infrared (SINFONI) (H+K-band) and NACO L'- and M'-band) data sets between 2002 and 2018 with additional COMIC/ADONIS+RASOIR (L'-band)⁷data of 1999. By analyzing the line maps of SINFONI, we identify a velocity of ∼200 km s⁻¹ from the tip to the tail. Furthermore, a combination of the multiwavelength data of NACO and SINFONI in the H-, K-, L'-, and M'-bands results in a two-component blackbody fit that implies that X7 is a dust-enshrouded stellar object. The observed ongoing elongation and orientation of X7 in the Brγ line maps and the NACO L'-band continuum indicate a wind arising at the position of Sgr A* or at the IRS16 complex. Observations after 2010 show that the dust and the gas shell seems to be decoupled in the projection from its stellar source S50. The data also implies that the tail of X7 thermally heats up due to the presence of S50. The gas emission at the tip is excited because of the related forward scattering (Mie scattering), which will continue to influence the shape of X7 in the near future. In addition, we find excited [Fe iii] lines, which together with the recently analyzed dusty sources and the Brγ-bar underline the uniqueness of this source.

Using the Insight-HXMT observations of GRS 1915+105 when it exhibits low-frequency quasiperiodic oscillations (QPOs), we measure the evolution of the QPO frequency along with disk inner radius and mass accretion rate. We find a tight positive correlation between the QPO frequency and mass accretion rate. Our results extend the finding of previous work with AstroSat to a larger range of accretion rates with independent instruments and observations. Treating the QPO frequency of GRS 1915+105 as the relativistic dynamic frequency of a truncated disk, we are able to confirm the high spin nature of the black hole in GRS 1915+105. We also address the potential of our finding to test general relativity in the future.

This is the third sequel in a series discussing the discovery of various types of extragalactic transients with the James Webb Space Telescope (JWST) in a narrow-field (∼0.1 deg²), moderately deep (m_AB ∼ 27 mag) survey. In this part we focus on the detectability and observational characteristics of direct-collapse black holes (DCBHs) and tidal disruption events (TDEs) around them. We use existing models for DCBH accretion luminosities and spectra, as well as for TDE light curves, and find that accreting DCBH seeds may be bright enough for detection up to z ∼ 7 with JWST NIRCam imaging. TDEs of massive (M ≳ 50 M_⊙) stars around them can enhance the chance for discovering them as transient objects, although the rate of such events is low, a few per survey time. TDEs around nonaccreting black holes of M ∼ 10⁶M_⊙ may also be detected at z < 7 redshifts in the redder NIRCam bands between 3 and 5 μs. It is also shown that accreting DCBHs appear separate from supernovae on the NIRCam color–color plot, but TDEs from quiescent black holes fall in nearly the same color range as superluminous supernovae, which makes them more difficult to identify.

After the prediction of many sub- and super-Chandrasekhar (at least a dozen for the latter) limiting-mass white dwarfs (WDs), hence apparently a peculiar class of WDs, from the observations of luminosity of Type Ia supernovae, researchers have proposed various models to explain these two classes of WD separately. We earlier showed that these two peculiar classes of WD, along with the regular WD, can be explained by a single form of the f(R) gravity, whose effect is significant only in the high-density regime, and it almost vanishes in the low-density regime. However, since there is no direct detection of such a WD, it is difficult to single out one specific theory from the zoo of modified theories of gravity. We discuss the possibility of direct detection of such a WD in gravitational wave (GW) astronomy. It is well known that in f(R) gravity more than two polarization modes are present. We estimate the amplitudes of all the relevant modes for the peculiar and the regular WD. We further discuss the possibility of their detections through future-based GW detectors, such as LISA, ALIA, DECIGO, BBO, or the Einstein Telescope, and thereby put constraints on or rule out various modified theories of gravity. This exploration links the theory with possible observations through GW in f(R) gravity.

Helioseismic waves observable at the solar surface can be used to probe the properties of the Sun's interior. By measuring helioseismic travel times between different location on the surface, flows and other interior properties can be inferred using so-called sensitivity kernels that relate the amount of travel-time shift with variations in interior properties. In particular, sensitivity kernels for flows have been developed in the past, using either ray or Born approximation, and have been used to infer solar interior flows such as the meridional circulation, which is of particular interest for understanding the structure and dynamics of the Sun. Here we introduce a new method for deriving three-dimensional sensitivity kernels for large-scale horizontal flows in the solar interior. We perform global-Sun wave-propagation simulations through 784 small flow perturbations placed individually in the interior of a simulated Sun, and measure the shifts in helioseismic travel times caused by these perturbations. Each measurement corresponds to a linear equation connecting the flow perturbation velocities and the sensitivity kernels. By solving the resulting large set of coupled linear equations, we derive three-dimensional sensitivity kernels for horizontal flows, which have a longitudinal component (parallel to the wave's travel direction) and a transverse component (perpendicular to the wave's travel direction). The kernels exhibit a "banana" shape, similar to kernels derived using Born-approximation methods, and show that transverse components are not negligible in inversions for interior flows.

We present FANTASY (Finally A Numerical Trajectory Algorithm both Straightforward and sYmplectic), a user-friendly, open-source symplectic geodesic integrator written in Python. FANTASY is designed to work "out of the box" and does not require anything from the user aside from the metric and the initial conditions for the geodesics. FANTASY efficiently computes derivatives up to machine precision using automatic differentiation, allowing the integration of geodesics in arbitrary space(times) without the need for the user to manually input Christoffel symbols or any other metric derivatives. Further, FANTASY utilizes a Hamiltonian integration scheme that doubles the phase space, where two copies of the particle phase space are evolved together. This technique allows for an integration scheme that is both explicit and symplectic, even when the Hamiltonian is not separable. FANTASY comes prebuilt with second- and fourth-order schemes, and is easily extendable to higher-order schemes. FANTASY also includes an automatic Jacobian calculator that allows for coordinate transformations to be done automatically.

The emission feature of intermittent pulsars is significant for understanding the pulsar emission mechanism. Using the observational evidence of radio emissions turning on and off and the corresponding spin-down rates in these two states of an intermittent pulsar, we will examine the polar-cap potential drop, gap height, and curvature radii of a few intermittent pulsars within the regime of the pulsar polar-cap emission theory by applying the current loss and energy flux of particle flow to pulsar braking, which are generally associated with radio emission from the polar cap. It is seen that the polar-cap parameters of the intermittent pulsars are almost equal to their maximum values, which is the main prediction of the pulsar polar-cap theory with respect to the breaking of the radio emission. It is also noticed that the intermittent pulsars are distributed near the dipole death line in the $P\mbox{--}\dot{P}$ diagram, which is consistent with their emission features and the calculated polar-cap parameters. To further confirm the state switching of the intermittent pulsar, the relationships among spin-down rate, gap height, potential drop, and activity duty cycles of PSR B1931+24 are discussed. It is found that the gap height has an anticorrelation with the activity duty cycle, which indicates that the intermittency of the radio emission has a close connection to the gap height, as indicated by the pulsar polar-cap emission theory.

We explore upper limits for the largest avalanches or catastrophes in nonlinear energy dissipation systems governed by self-organized criticality. We generalize the idealized "straight" power-law size distribution and Pareto distribution functions in order to accommodate incomplete sampling, limited instrumental sensitivity, finite system-size effects, and "Black Swan" and "Dragon King" extreme events. Our findings are as follows. (i) Solar flares show no finite system-size limits up to L ≲ 200 Mm, but solar flare durations reveal an upper flare duration limit of ≲6 hr. (ii) Stellar flares observed with Kepler exhibit inertial ranges of E ≈ 10³⁴–10³⁷ erg, finite system-size ranges of E ≈ 10³⁷–10³⁸ erg, and extreme events at E ≈ (1–5) × 10³⁸ erg. (iii) The maximum flare energies of different spectral type stars (M, K, G, F, A, giants) reveal a positive correlation with the stellar radius, which indicates a finite system-size limit imposed by the stellar surface area. Fitting our finite system-size models to terrestrial data sets (earthquakes, wildfires, city sizes, blackouts, terrorism, words, surnames, web links) yields evidence (in half of the cases) for finite system-size limits and extreme events, which can be modeled with dual power-law size distributions.

Recent high-resolution simulations of early structure formation have shown that externally enriched halos may form some of the first metal-enriched stars. This study utilizes a 1 comoving Mpc³ high-resolution simulation to study the enrichment process of metal-enriched halos down to z = 9.3. Our simulation uniquely tracks the metals ejected from Population III stars, and we use this information to identify the origin of metals within metal-enriched halos. These halos show a wide range of metallicities, but we find that the source of metals for ≳50% of metal-enriched halos is supernova explosions of Population III stars occurring outside their virial radii. The results presented here indicate that external enrichment by metal-free stars dominates the enrichment process of halos with virial mass below 10⁶M_⊙ down to z = 9.3. Despite the prevalence of external enrichment in low-mass halos, Population II stars forming due to external enrichment are rare because of the small contribution of low-mass halos to the global star formation rate combined with low metallicities toward the center of these halos resulting from metal ejecta from external sources mixing from the outside in. The enriched stars that do form through this process have absolute metallicities below 10⁻³Z_⊙. We also find that the fraction of externally enriched halos increases with time: ∼90% of halos that are externally enriched have M_vir < 10⁶M_⊙, and that pair-instability supernovae contribute the most to the enrichment of the intergalactic medium as a whole and are thus are the predominant supernova type contributing to the external enrichment of halos.

The diffuse interstellar medium (ISM) is dynamic, and its chemistry and evolution are determined by shock fronts as well as photodissociation. Shocks are implied by the supersonic motions and velocity dispersion, often statistically called "turbulence". We compare models of magnetohydrodynamic (MHD) shocks, with speeds typical of cloud motions through the ISM (3–25 km s⁻¹) and densities typical of cold neutral gas (∼10² cm⁻³), to archival observations of the H i 21 cm line for gas kinematics, far-infrared emission for dust mass, and mid-infrared emission for high-resolution morphology, to identify shock fronts in three high-latitude cloud pairs with masses of order 50 M_⊙. The clouds have "heads" with extended "tails," and high-resolution images show arcs on the leading edges of the "heads" that could be individual shocks. The H i shows higher-velocity gas at the leading edges due to shock-accelerated material. For two cloud pairs, one cloud has an active shock indicated by broad and offset H i, while the other cloud has already been shocked and is predominantly "CO-dark" H₂. Two-dimensional MHD simulations for shocks parallel to the magnetic field for pairs of clouds show a remarkable similarity to observed cloud features, including merged "tails" due to aligned flow and magnetic field, which leads to lateral confinement downstream. A parallel alignment between magnetic field and gas flow may lead to formation of small molecular clouds.

Solar active regions and sunspots are believed to be formed by the emergence of strong toroidal magnetic flux from the solar interior. Modeling of such events has focused on the dynamics of compact magnetic entities, colloquially known as "flux tubes," often considered to be isolated magnetic structures embedded in an otherwise field-free environment. In this paper, we show that relaxing such idealized assumptions can lead to surprisingly different dynamics. We consider the rise of tube-like flux concentrations embedded in a large-scale volume-filling horizontal field in an initially quiescent adiabatically stratified compressible fluid. In a previous letter, we revealed the unexpected major result that concentrations whose twist is aligned with the background field at the bottom of the tube are more likely to rise than the opposite orientation (for certain values of parameters). This bias leads to a selection rule which, when applied to solar dynamics, is in agreement with the observations known as the solar hemispheric helicity rule(s) (SHHR). Here, we examine this selection mechanism in more detail than was possible in the earlier letter. We explore the dependence on parameters via simulations, delineating the Selective Rise Regime, where the bias operates. We provide a theoretical model to predict and explain the simulation dynamics. Furthermore, we create synthetic helicity maps from Monte Carlo simulations to mimic the SHHR observations, and to demonstrate that our mechanism explains the observed scatter in the rule, as well as its variation over the solar cycle.

The polarization properties of radio sources powered by an Active Galactic Nucleus (AGN) have attracted considerable attention because of the significance of magnetic fields in the physics of these sources, their use as probes of plasma along the line of sight, and as a possible contaminant of polarization measurements of the cosmic microwave background. For each of these applications, a better understanding of the statistics of polarization in relation to source characteristics is crucial. In this paper, we derive the median fractional polarization, Π_0,med, of large samples of radio sources with 1.4 GHz flux density 6.6 < S_1.4 < 70 mJy, by stacking 1.4 GHz NVSS polarized intensity as a function of angular size derived from the FIRST survey. Five samples with deconvolved mean angular size 18 to 82 and two samples of symmetric double sources are analyzed. These samples represent most sources smaller than or near the median angular size of the mJy radio source population We find that the median fractional polarization Π_0,med at 1.4 GHz is a strong function of source angular size ≲5'' and a weak function of angular size for larger sources up to ∼8''. We interpret our results as depolarization inside the AGN host galaxy and its circumgalactic medium. The curvature of the low-frequency radio spectrum is found to anticorrelate with Π_0,med, a further sign that depolarization is related to the source.

Stellar-mass estimates of massive galaxies are susceptible to systematic errors in their photometry, due to their extended light profiles. In this study, we use data from the Dragonfly Wide Field Survey to accurately measure the total luminosities and colors of nearby massive galaxies. The low surface brightness limits of the survey (μ_g ≈ 31 mag arcsec⁻² on a 1' scale) allow us to implement a method, based on integrating the 1D surface brightness profile, that is minimally dependent on any parameterization. We construct a sample of 1188 massive galaxies with $\mathrm{log}{M}_{* }/{M}_{\odot }\gt 10.75$ based on the Galaxy Mass and Assembly (GAMA) survey and measure their total luminosities and g − r colors. We then compare our measurements to various established methods applied to imaging from the Sloan Digital Sky Survey (SDSS), focusing on those favored by the GAMA survey. In general, we find that galaxies are brighter in the r band by an average of ∼0.05 mag and bluer in g − r colors by ∼0.06 mag compared to the GAMA measurements. These two differences have opposite effects on the stellar-mass estimates. The total luminosities are larger by 5% but the mass-to-light ratios are lower by ∼10%. The combined effect is that the stellar-mass estimate of massive galaxies decreases by 7%. This, in turn, implies a small change in the number density of massive galaxies: ≤30% at $\mathrm{log}{M}_{* }/{M}_{\odot }\geqslant 11$.

We discovered a new growth mode of dust grains to kilometer-size bodies in protoplanetary disks that evolve via viscous accretion and magnetically driven disk winds (MDWs). We solved an approximate coagulation equation of dust grains with time-evolving disks that consist of both gas and solid components using a one-dimensional model. With grain growth, all solid particles initially drift inward toward the central star due to the gas drag force. However, the radial profile of gas pressure, P, is modified by the MDW that disperses the gas in an inside-out manner. Consequently, a local concentration of solid particles is created by the converging radial flux of drifting dust grains at the location with a convex-upward profile of P. When the dimensionless stopping time, St, exceeds unity there, the solid particles spontaneously reach the growth-dominated state because of the positive feedback between the suppressed radial drift and the enhanced accumulation of dust particles that drift from the outer part. Once the solid particles are in the drift-limited state, the above-mentioned condition of St $\gtrsim \,1$ for dust growth is equivalent to Σ_d/Σ_g ≳ η, where Σ_d/Σ_g is the dust-to-gas surface-density ratio and η is the dimensionless radial pressure-gradient force. As a consequence of the successful growth of dust grains, a ring-like structure containing planetesimal-size bodies is formed at the inner part of the protoplanetary disks. Such a ring-shaped concentration of planetesimals is expected to play a vital role in the subsequent planet formation.

We study the collimation and acceleration of jets in the nearby giant radio galaxy NGC 315, using multifrequency Very Long Baseline Array observations and archival High Sensitivity Array and Very Large Array data. We find that the jet geometry transitions from a semi-parabolic shape into a conical/hyperbolic shape at a distance of ≈10⁵ gravitational radii. We constrain the frequency-dependent position of the core, from which we locate the jet base. The jet collimation profile in the parabolic region is in good agreement with the steady axisymmetric force-free electrodynamic solution for the outermost poloidal magnetic field line anchored to the black hole event horizon on the equatorial plane, similar to the nearby radio galaxies M87 and NGC 6251. The velocity field derived from the asymmetry in brightness between the jet and counterjet shows gradual acceleration up to the bulk Lorentz factor of Γ ∼ 3 in the region where the jet collimation occurs, confirming the presence of the jet acceleration and collimation zone. These results suggest that the jets are collimated by the pressure of the surrounding medium and accelerated by converting Poynting flux to kinetic energy flux. We discover limb brightening of the jet in a limited distance range where the angular resolution of our data is sufficient to resolve the jet transverse structure. This indicates that either the jet has a stratified velocity field of fast-inner and slow-outer layers or the particle acceleration process is more efficient in the outer layer owing to the interaction with the surroundings on parsec scales.

We compare abundance ratio trends in a sample of ∼11,000 Milky Way bulge stars (R_GC < 3 kpc) from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) to those of APOGEE stars in the Galactic disk (5 kpc < R_GC < 11 kpc). We divide each sample into low-Ia (high-[Mg/Fe]) and high-Ia (low-[Mg/Fe]) populations, and in each population, we examine the median trends of [X/Mg] versus [Mg/H] for elements X = Fe, O, Na, Al, Si, P, S, K, Ca, V, Cr, Mn, Co, Ni, Cu, and Ce. To remove small systematic trends of APOGEE abundances with stellar $\mathrm{log}(g)$, we resample the disk stars to match the $\mathrm{log}(g)$ distributions of the bulge data. After doing so, we find nearly identical median trends for low-Ia disk and bulge stars for all elements. High-Ia trends are similar for most elements, with noticeable (0.05–0.1 dex) differences for Mn, Na, and Co. The close agreement of abundance trends (with typical differences ≲0.03 dex) implies that similar nucleosynthetic processes enriched bulge and disk stars despite the different star formation histories and physical conditions of these regions. For example, we infer that differences in the high-mass slope of the stellar initial mass function between disk and bulge must have been ≲0.30. This agreement, and the generally small scatter about the median sequences, means that one can predict all of a bulge star's APOGEE abundances with good accuracy knowing only its measured [Mg/Fe] and [Mg/H] and the observed trends of disk stars.

We investigate what drives the redshift evolution of the typical electron density (n_e) in star-forming galaxies, using a sample of 140 galaxies drawn primarily from KMOS^3D (0.6 < z < 2.6) and 471 galaxies from SAMI (z < 0.113). We select galaxies that do not show evidence of active galactic nucleus activity or outflows to constrain the average conditions within H ii regions. Measurements of the [S ii]λ6716/[S ii]λ6731 ratio in four redshift bins indicate that the local n_e in the line-emitting material decreases from 187${}_{-132}^{+140}$ cm⁻³ at z ∼ 2.2 to 32${}_{-9}^{+4}$ cm⁻³ at z ∼ 0, consistent with previous results. We use the Hα luminosity to estimate the rms n_e averaged over the volumes of star-forming disks at each redshift. The local and volume-averaged n_e evolve at similar rates, hinting that the volume filling factor of the line-emitting gas may be approximately constant across 0 ≲ z ≲ 2.6. The KMOS^3D and SAMI galaxies follow a roughly monotonic trend between n_e and star formation rate, but the KMOS^3D galaxies have systematically higher n_e than the SAMI galaxies at a fixed offset from the star-forming main sequence, suggesting a link between the n_e evolution and the evolving main sequence normalization. We quantitatively test potential drivers of the density evolution and find that n_e(rms) $\simeq {n}_{{{\rm{H}}}_{2}}$, suggesting that the elevated n_e in high-z H ii regions could plausibly be the direct result of higher densities in the parent molecular clouds. There is also tentative evidence that n_e could be influenced by the balance between stellar feedback, which drives the expansion of H ii regions, and the ambient pressure, which resists their expansion.

We conduct an all-sky search for continuous gravitational waves in the LIGO O2 data from the Hanford and Livingston detectors. We search for nearly monochromatic signals with frequency 20.0 Hz ≤ f ≤ 585.15 Hz and spin-down $-2.6\times {10}^{-9}\,\mathrm{Hz}\,{{\rm{s}}}^{-1}\leqslant \dot{f}\leqslant 2.6\times {10}^{-10}$ Hz s⁻¹. We deploy the search on the Einstein@Home volunteer-computing project and follow-up the waveforms associated with the most significant results with eight further search stages, reaching the best sensitivity ever achieved by an all-sky survey up to 500 Hz. Six of the inspected waveforms pass all the stages but they are all associated with hardware injections, which are fake signals simulated at the LIGO detector for validation purposes. We recover all these fake signals with consistent parameters. No other waveform survives, so we find no evidence of a continuous gravitational wave signal at the detectability level of our search. We constrain the h₀ amplitude of continuous gravitational waves at the detector as a function of the signal frequency, in half-Hz bins. The most constraining upper limit at 163.0 Hz is h₀ = 1.3 × 10⁻²⁵, at the 90% confidence level. Our results exclude neutron stars rotating faster than 5 ms with equatorial ellipticities larger than 10⁻⁷ closer than 100 pc. These are deformations that neutron star crusts could easily support, according to some models.

Radio sources at the highest redshifts can provide unique information on the first massive galaxies and black holes, the densest primordial environments, and the epoch of reionization. The number of astronomical objects identified at z > 6 has increased dramatically over the last few years, but previously only three radio-loud (R₂₅₀₀ = f_{ν,5 GHz}/f_{ν,2500 Å} > 10) sources had been reported at z > 6, with the most distant being a quasar at z = 6.18. Here we present the discovery and characterization of PSO J172.3556+18.7734, a radio-loud quasar at z = 6.823. This source has an Mg ii-based black hole mass of ∼3 × 10⁸M_⊙ and is one of the fastest accreting quasars, consistent with super-Eddington accretion. The ionized region around the quasar is among the largest measured at these redshifts, implying an active phase longer than the average lifetime of the z ≳ 6 quasar population. From archival data, there is evidence that its 1.4 GHz emission has decreased by a factor of two over the last two decades. The quasar's radio spectrum between 1.4 and 3.0 GHz is steep (α = −1.31). Assuming the measured radio slope and extrapolating to rest-frame 5 GHz, the quasar has a radio-loudness parameter R₂₅₀₀ ∼ 90. A second steep radio source (α = −0.83) of comparable brightness to the quasar is only 231 away (∼120 kpc at z = 6.82; projection probability <2%), but shows no optical or near-infrared counterpart. Further follow-up is required to establish whether these two sources are physically associated.

We present numerical simulations of misaligned disks around a spinning black hole covering a range of parameters. Previous simulations have shown that disks that are strongly warped by a forced precession—in this case, the Lense–Thirring effect from the spinning black hole—can break apart into discrete disks or rings that can behave quasi-independently for short timescales. With the simulations we present here, we confirm that thin and highly inclined disks are more susceptible to disk tearing than thicker disks or those with lower inclination, and we show that lower values of the disk viscosity parameter lead to instability at lower warp amplitudes. This is consistent with detailed stability analysis of the warped disk equations. We find that the growth rates of the instability seen in the numerical simulations are similar across a broad range of parameters, and are of the same order as the predicted growth rates. However, we did not find the expected trend of growth rates with viscosity parameter. This may indicate that the growth rates are affected by numerical resolution, or that the wavelength of the fastest-growing mode is a function of local disk parameters. Finally, we also find that disk tearing can occur for disks with a viscosity parameter that is higher than predicted by a local stability analysis of the warped disk equations. In this case, the instability manifests differently, producing large changes in the disk tilt locally in the disk, rather than the large changes in disk twist that typically occur in lower-viscosity disks.

Accretion disks around black holes power some of the most luminous objects in the universe. Disks that are misaligned to the black hole spin can become warped over time by Lense–Thirring precession. Recent work has shown that strongly warped disks can become unstable, causing the disk to break into discrete rings producing a more dynamic and variable accretion flow. In a companion paper, we present numerical simulations of this instability and the resulting dynamics. In this paper, we discuss the implications of this dynamics for accreting black hole systems, with particular focus on the variability of active galactic nuclei (AGN). We discuss the timescales on which variability might manifest, as well as the impact of the observer orientation with respect to the black hole spin axis. When the disk warp is unstable near the inner edge of the disk, we find quasi-periodic behavior of the inner disk, which may explain the recent quasi-periodic eruptions observed in, for example, the Seyfert 2 galaxy GSN 069 and in the galactic nucleus of RX J1301.9+2747. These eruptions are thought to be similar to the "heartbeat" modes observed in some X-ray binaries (e.g., GRS 1915+105 and IGR J17091-3624). When the instability manifests at larger radii in the disk, we find that the central accretion rate can vary on timescales that may be commensurate with, e.g., changing-look AGN. We therefore suggest that some of the variability properties of accreting black hole systems may be explained by the disk being significantly warped, leading to disk tearing.

Magnetars are highly magnetized neutron stars that are characterized by recurrent emission of short-duration bursts in soft gamma-rays/hard X-rays. Recently, FRB 200428 was found to be associated with an X-ray burst from a Galactic magnetar. Two fast radio bursts show mysterious periodic activity. However, it is unclear whether magnetar X-ray bursts are periodic phenomena. In this paper, we investigate the activity period of SGR 1806-20. More than 3000 short bursts observed by different telescopes are collected, including the observations of RXTE, HETE-2, ICE, and Konus. We consider the observation windows and divide the data into two subsamples to alleviate the effect of uneven sampling. The epoch-folding and Lomb–Scargle methods are used to derive the period of the short bursts. We find a possible period of about 398.20 ± 25.45 days, but other peaks exist in the periodograms. If the period is real, the connection between short bursts of magnetars and fast radio bursts should be investigated extensively.

We present results of subarcsec Atacama Large Millimeter/submillimeter Array observations of CO(2–1) and CO(5–4) toward a massive main-sequence galaxy at z = 1.45 in the Subaru-XMM/Newton Deep Survey/UDS field, aiming at examining the internal distribution and properties of molecular gas in the galaxy. Our target galaxy consists of the bulge and disk, and has a UV clump in the Hubble Space Telescope images. The CO emission lines are clearly detected, and the CO(5–4)/CO(2–1) flux ratio (R₅₂) is ∼1, similar to that of the Milky Way. Assuming a metallicity-dependent CO-to-H₂ conversion factor and a CO(2–1)/CO(1–0) flux ratio of 2 (the Milky Way value), the molecular gas mass and the gas-mass fraction (f_gas = ratio of the molecular gas mass to the molecular gas mass + stellar mass) are estimated to be ∼1.5 × 10¹¹M_⊙ and ∼0.55, respectively. We find that R₅₂ peak coincides with the position of the UV clump and that its value is approximately twice higher than the galactic average. This result implies a high gas density and/or high temperature in the UV clump, which qualitatively agrees with a numerical simulation of a clumpy galaxy. The CO(2–1) distribution is well represented by a rotating-disk model, and its half-light radius is ∼2.3 kpc. Compared to the stellar distribution, the molecular gas is more concentrated in the central region of the galaxy. We also find that f_gas decreases from ∼0.6 at the galactic center to ∼0.2 at three times the half-light radius, indicating that the molecular gas is distributed in the more central region of the galaxy than stars and seems to be associated with the bulge rather than with the stellar disk.

Observations of scattered light and thermal emission from hot Jupiter exoplanets have suggested the presence of inhomogeneous aerosols in their atmospheres. 3D general circulation models (GCMs) that attempt to model the effects of aerosols have been developed to understand the physical processes that underlie their dynamical structures. In this work, we investigate how different approaches to aerosol modeling in GCMs of hot Jupiters affect high-resolution thermal emission spectra throughout the duration of the planet's orbit. Using results from a GCM with temperature-dependent cloud formation, we calculate spectra of a representative hot Jupiter with different assumptions regarding the vertical extent and thickness of clouds. We then compare these spectra to models in which clouds are absent or simply post-processed (i.e., added subsequently to the completed clear model). We show that the temperature-dependent treatment of clouds in the GCM produces high-resolution emission spectra that are markedly different from the clear and post-processed cases—both in the continuum flux levels and line profiles—and that increasing the vertical extent and thickness of clouds leads to bigger changes in these features. We evaluate the net Doppler shifts of the spectra induced by global winds and the planet's rotation and show that they are strongly phase dependent, especially for models with thicker and more extended clouds. This work further demonstrates the importance of radiative feedback in cloudy atmospheric models of hot Jupiters, as this can have a significant impact on interpreting spectroscopic observations of exoplanet atmospheres.

Polar crown filaments (PCFs) are formed above the polarity inversion line, which separates unipolar polar fields and the nearest dispersed fields. They are important features in studying solar polar fields and their cyclical variations. Due to the relatively weak field strength and projection effects, measuring polar magnetic fields is more difficult than obtaining the field strengths concentrated in active regions at lower latitudes. "Rush-to-the-pole" of PCFs represent the progress of unipolar polar fields from the previous solar cycle being canceled by the dispersed fields generated in the current cycle. Such progress is a good indicator of the polarity reversal in the polar areas and a precursor for the solar maximum. In this study, PCFs are identified from a 100 yr archive, covering cycles 16–24. This archive consists of full-disk Hα images obtained from the Kodaikanal Solar Observatory of the Indian Institute of Astrophysics, Kanzelhöhe Solar Observatory, and Big Bear Solar Observatory. The poleward migration speeds are measured and show an obvious asymmetry in the northern and southern hemispheres. In addition, our results show that the PCFs usually reach their highest latitudes first in the northern hemisphere, except cycle 17. Similarly, previous studies show that the magnetic field reversed first at the north pole in six out of nine cycles. We also compare the temporal variations of PCF migration and the latitude gradient factor of the differential rotation, which shows a trend in the southern hemisphere. Moreover, the migration speed of PCFs does not seem to be well correlated with the maximum sunspot numbers.

The polar precursor method is widely considered to be the most robust physically motivated method to predict the amplitude of an upcoming solar cycle. It uses indicators of the magnetic field concentrated near the poles around the sunspot minimum. Here, we present an extensive analysis of the performance of various such predictors, based on both observational data (Wilcox Solar Observatory (WSO) magnetograms, Mount Wilson Observatory polar faculae counts, and Pulkovo A(t) index) and outputs (polar cap magnetic flux and global dipole moment) of various existing flux transport dynamo models. We calculate Pearson correlation coefficients (r) of the predictors with the next cycle amplitude as a function of time measured from several solar cycle landmarks: setting r = 0.8 as a lower limit for acceptable predictions, we find that observations and models alike indicate that the earliest time when the polar predictor can be safely used is 4 yr after the polar field reversal. This is typically 2–3 yr before the solar minimum and about 7 yr before the predicted maximum, considerably extending the usual temporal scope of the polar precursor method. Reevaluating the predictors another 3 yr later, at the time of the solar minimum, further increases the correlation level to r ≳ 0.9. As an illustration of the result, we determine the predicted amplitude of Cycle 25 based on the value of the WSO polar field at the now official minimum date of 2019 December as 126 ± 3. A forecast based on the value in early 2017, 4 yr after the polar reversal would have only differed from this final prediction by 3.1 ± 14.7%.

The equatorial current sheets outside the light cylinder (LC) are thought to be promising sites of high-energy emission based on the results of recent numerical simulations. We explore the pulsar light curves and energy spectra by computing the curvature radiation based on the FIDO magnetospheres. The FIDO magnetospheres with a near force-free regime inside the LC and a finite but high conductivity outside the LC are constructed using a spectral algorithm. The pulsar high-energy emission properties are explored by integrating the trajectories of the test particles under the influence of both the accelerating electric field and the curvature radiation losses. As an application, we compare the predicted energy-dependent light curves and energy spectra with those of the Crab and Vela pulsars published in the Fermi 2PC catalog. We find that the observed characteristics of the light curves and energy spectra from the Crab and Vela pulsars can be well reproduced by the FIDO model.

The question why the solar corona is much hotter than the visible solar surface still puzzles solar researchers. Most theories of the coronal heating involve a tight coupling between the coronal magnetic field and the associated thermal structure. This coupling is based on two facts: (i) the magnetic field is the main source of the energy in the corona and (ii) the heat transfer preferentially happens along the magnetic field, while is suppressed across it. However, most of the information about the coronal heating is derived from the analysis of extreme ultraviolet or soft X-ray emissions, which are not explicitly sensitive to the magnetic field. This paper employs another electromagnetic channel—the sunspot-associated microwave gyroresonant emission, which is explicitly sensitive to both the magnetic field and thermal plasma. We use nonlinear force-free field reconstructions of the magnetic skeleton dressed with a thermal structure as prescribed by a field-aligned hydrodynamics to constrain the coronal heating model. We demonstrate that the microwave gyroresonant emission is extraordinarily sensitive to details of the coronal heating. We infer heating model parameters consistent with observations.

We present the first detailed observational picture of a possible ongoing massive cluster hierarchical assembly in the Galactic disk as revealed by the analysis of the stellar full phase space (3D positions and kinematics and spectro-photometric properties) of an extended area (6° diameter) surrounding the well-known h and χ Persei double stellar cluster in the Perseus Arm. Gaia-EDR3 shows that the area is populated by seven comoving clusters, three of which were previously unknown, and by an extended and quite massive (M ∼ 10⁵M_⊙) halo. All stars and clusters define a complex structure with evidence of possible mutual interactions in the form of intra-cluster overdensities and/or bridges. They share the same chemical abundances (half-solar metallicity) and age (t ∼ 20 Myr) within a small confidence interval and the stellar density distribution of the surrounding diffuse stellar halo resembles that of a cluster-like stellar system. The combination of these pieces of evidence suggests that stars distributed within a few degrees from h and χ Persei are part of a common, substructured stellar complex that we named LISCA I. Comparison with results obtained through direct N-body simulations suggest that LISCA I may be at an intermediate stage of an ongoing cluster assembly that can eventually evolve in a relatively massive (a few times 10⁵M_⊙) stellar system. We argue that such a cluster formation mechanism may be quite efficient in the Milky Way and disk-like galaxies and, as a consequence, it has a relevant impact on our understanding of cluster formation efficiency as a function of the environment and redshift.

We present evidence that a magnetic flux rope was formed before a coronal mass ejection (CME) and its associated long-duration flare during a pair of preceding confined eruptions and associated impulsive flares in a compound event in NOAA Active Region 12371. Extreme-ultraviolet images and the extrapolated nonlinear force-free field show that the first two (impulsive) flares, SOL2015-06-21T01:42, result from the confined eruption of highly sheared low-lying flux, presumably a seed flux rope. The eruption spawns a vertical current sheet, where magnetic reconnection creates flare ribbons and loops, a nonthermal microwave source, and a sigmoidal hot channel that can only be interpreted as a magnetic flux rope. Until the subsequent long-duration flare, SOL2015-06-21T02:36, the sigmoid's elbows expand, while its center remains stationary, suggesting nonequilibrium but not yet instability. The "flare reconnection" during the confined eruptions acts like "tether-cutting reconnection" whose flux feeding of the rope leads to instability. The subsequent full eruption is seen as an accelerated rise of the entire hot channel, seamlessly evolving into the fast halo CME. Both the confined and ejective eruptions are consistent with the onset of the torus instability in the dipped decay index profile that results from the region's two-scale magnetic structure. We suggest that the formation or enhancement of a nonequilibrium but stable flux rope by confined eruptions is a generic process occurring prior to many CMEs.

Compact starburst galaxies are thought to include many or most of the galaxies from which substantial Lyman continuum emission can escape into the intergalactic medium. Li & Malkan used Sloan Digital Sky Survey photometry to find a population of such starburst galaxies at z ∼ 0.5. They were discovered by their extremely strong [O iii] λλ4959+5007 emission lines, which produce a clearly detectable excess brightness in the i bandpass, compared with surrounding filters. We therefore used the Hubble Space Telescope (HST)/COS spectrograph to observe two of the newly discovered i-band excess galaxies around their Lyman limits. One has strongly detected continuum below its Lyman limit, corresponding to a relative escape fraction of ionizing photons of 20% ± 2%. The other, which is less compact in UV imaging, has a 2σ upper limit to its Lyman escape fraction of <5%. Before the UV spectroscopy, the existing data could not distinguish these two galaxies. Although a sample of two is hardly sufficient for statistical analysis, it shows the possibility that some fraction of these strong [O iii] emitters as a class have ionizing photons escaping. The differences might be determined by the luck of our particular viewing geometry. Obtaining the HST spectroscopy revealed that the Lyman-continuum-emitting galaxy differs in having no central absorption in its prominent Lyα emission-line profile. The other target, with no escaping Lyman continuum, shows the more common double-peaked Lyα emission.

We report the most detailed 1–3 GHz radio continuum emission map of the nearest region of massive-star formation, the Carina Nebula. As part of a large program with the Australia Telescope Compact Array, we have covered ∼12 deg², achieving an angular resolution of ∼16'', representing the largest and most complete map of the radio continuum to date. Our continuum map shows a spectacular and complex distribution of emission across the nebula, with multiple structures such as filaments, shells, and fronts across a wide range of size scales. The ionization fronts have advanced far into the southern and northern region of the Galactic plane, as fronts are clearly detected at distances of ∼80 pc from the stellar clusters in the center. We estimated an ionization photon luminosity Q_H = (7. 8 ± 0.8) × 10⁵⁰ s⁻¹, which corresponds to ∼85% of the total value obtained from stellar population studies. Thus, approximately 15% of the ionizing flux has escaped from the nebula into the diffuse Galactic interstellar medium. Comparison between radio continuum and the hydrogen atomic and molecular gas maps offers a clear view of the bipolar outflow driven by the energy released by the massive stellar clusters that also affects the fraction of molecular gas across the nebula. Comparison between 8 μm and 70 μm emission maps and the radio continuum reveals how the hot gas permeates through the molecular cloud; shapes the material into features such as pillars, small shells, and arc-like structures; and ultimately escapes.

The dielectric function of interstellar dust material is modeled using observations of extinction and polarization in the infrared, together with estimates for the mass of interstellar dust. The "astrodust" material is assumed to be a mix of amorphous silicates and other materials, including hydrocarbons producing an absorption feature at 3.4 μm. The detailed shape of the 10 μm polarization profile depends on the assumed porosity and grain shape, but the 10 μm spectropolarimetric data are not yet good enough to clearly favor one shape over another, nor to constrain the porosity. The expected 3.4 μm feature polarization is consistent with existing upper limits, provided the 3.4 μm absorption is preferentially located in grain surface layers; a separate population of non-aligned carbonaceous grains is not required. We predict the 3.4 μm polarization feature to be (Δp)_{3.4 μm}/p(10 μm) ≈ 0.016, just below current upper limits. Polarization by the same grains at submillimeter wavelengths is also calculated.

We provide a simple geometric explanation for the source of switchbacks and associated large and one-sided transverse flows in the solar wind observed by the Parker Solar Probe (PSP). The more radial, sub-Parker spiral structure of the heliospheric magnetic field observed previously by Ulysses, ACE, and STEREO is created within rarefaction regions where footpoint motion from the source of fast into slow wind at the Sun creates a magnetic fieldline connection across solar wind speed shear. Conversely, when footpoints move from the source of slow wind into faster wind, a super-Parker spiral field structure is formed: below the Alfvén critical point, one-sided transverse field-aligned flows develop; above the Alfvén critical point, the field structure contracts between adjacent solar wind flows, and the radial field component decreases in magnitude with distance from the Sun, eventually reversing into a switchback. The sub-Parker and super-Parker spirals behave functionally as opposites. Observations from PSP confirm the paucity of switchbacks within rarefaction regions and immediately outside these rarefaction regions, we observe numerous switchbacks in the magnetic field that are directly associated with abrupt transients in solar wind speed. The magnetic field strength, the radial component of the magnetic field, the speed gradients, radial Alfvén speed, and the ratio of the sound speed to the radial Alfvén speed all conform to predictions based on the sub-Parker and super-Parker spirals within rarefaction regions and solar wind speed enhancements (spikes or jets), respectively. Critically, the predictions associated with the super-Parker spiral naturally explain the observations of switchbacks being associated with unexpectedly large and one-sided tangential flows.

In Wada et al. (2019), we proposed for the first time that a new class of planets, blanets, can be formed around supermassive black holes in the galactic center. Here, we investigate the dust coagulation processes and physical conditions of the blanet formation outside the snowline (r_snow ∼ several parsecs) in more detail, especially considering the effect of the radial drift of the dust aggregates. We found that a dimensionless parameter $\alpha ={v}_{t}^{2}/{c}_{s}^{2}$, where v_t is the turbulent velocity and c_s is the sound velocity, describing the turbulent viscosity should be smaller than 0.04 in the circumnuclear disk to prevent the destruction of the aggregates due to collision. The formation timescale of blanets τ_GI at r_snow is, τ_GI ≃ 70–80 Myr for α = 0.01 − 0.04 and M_BH = 10⁶M_⊙. The mass of the blanets ranges from ∼20M_E to 3000M_E in r < 4 pc for α = 0.02 (M_E is the Earth mass), which is in contrast with 4M_E–6M_E for the case without the radial drift. Our results suggest that blanets could be formed around relatively low-luminosity active galactic nuclei (L_bol ∼ 10⁴² erg s⁻¹) during their lifetime (≲10⁸ yr).