Table of contents

We report the lowest-frequency measurements of gamma-ray burst (GRB) 171205A with the upgraded Giant Metrewave Radio Telescope (uGMRT) covering a frequency range of 250–1450 MHz and a period of 4–937 days. It is the first GRB afterglow detected in the 250–500 MHz frequency range and the second brightest GRB detected with the uGMRT. Even though the GRB was observed for nearly 1000 days, there is no evidence of a transition to a nonrelativistic regime. We also analyzed the archival Chandra X-ray data on day ∼70 and day ∼200. We also found no evidence of a jet break from the analysis of combined data. We fit synchrotron afterglow emission arising from a relativistic, isotropic, self-similar deceleration as well as from a shock breakout of a wide-angle cocoon. Our data also allowed us to discern the nature and the density of the circumburst medium. We found that the density profile deviates from a standard constant density medium and suggests that the GRB exploded in a stratified wind-like medium. Our analysis shows that the lowest-frequency measurements covering the absorbed part of the light curves are critical to unraveling the GRB environment. Our data combined with other published measurements indicate that the radio afterglow has a contribution from two components: a weak, possibly slightly off-axis jet and a surrounding wider cocoon, consistent with the results of Izzo et al. The cocoon emission likely dominates at early epochs, whereas the jet starts to dominate at later epochs, resulting in flatter radio light curves.

PKS 1413+135 is one of the most peculiar blazars known. Its strange properties led to the hypothesis almost four decades ago that it is gravitationally lensed by a mass concentration associated with an intervening galaxy. It exhibits symmetric achromatic variability, a rare form of variability that has been attributed to gravitational milli-lensing. It has been classified as a BL Lac object, and is one of the rare objects in this class with a visible counterjet. BL Lac objects have jet axes aligned close to the line of sight. It has also been classified as a compact symmetric object—objects that have jet axes not aligned close to the line of sight. Intensive efforts to understand this blazar have hitherto failed to resolve even the questions of the orientation of the relativistic jet and the host galaxy. Answering these two questions is important because they challenge our understanding of jets in active galactic nuclei and the classification schemes we use to describe them. We show that the jet axis is aligned close to the line of sight and PKS 1413+135 is almost certainly not located in the apparent host galaxy, but is a background object in the redshift range 0.247 < z < 0.5. The intervening spiral galaxy at z = 0.247 provides a natural host for the putative lens responsible for symmetric achromatic variability and is shown to be a Seyfert 2 galaxy. We also show that, as for the radio emission, a "multizone" model is needed to account for the high-energy emission.

We report new observations toward the hyperluminous dusty starbursting major merger ADFS-27 (z = 5.655), using the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA). We detect CO (J = 2 → 1), CO (J = 8 → 7), CO (J = 9 → 8), CO (J = 10 → 9), and H₂O (3₁₂ → 2₂₁) emission, and a P Cygni−shaped OH⁺ (1₁ → 0₁) absorption/emission feature. We also tentatively detect H₂O (3₂₁ → 3₁₂) and OH⁺ (1₂ → 0₁) emission and CH⁺ (J = 1 → 0) absorption. We find a total cold molecular mass of M_gas = (2.1 ± 0.2) × 10¹¹ (α_CO/1.0) M_⊙. We also find that the excitation of the star-forming gas is overall moderate for a z > 5 dusty starburst, which is consistent with its moderate dust temperature. A high-density, high kinetic temperature gas component embedded in the gas reservoir is required to fully explain the CO line ladder. This component is likely associated with the "maximum starburst" nuclei in the two merging galaxies, which are separated by only 140 ± 13 km s⁻¹ along the line of sight and 9.0 kpc in projection. The kinematic structure of both components is consistent with galaxy disks, but this interpretation remains limited by the spatial resolution of the current data. The OH⁺ features are only detected toward the northern component, which is also the one that is more enshrouded in dust and thus remains undetected up to 1.6 μm even in our sensitive new Hubble Space Telescope Wide Field Camera 3 imaging. The absorption component of the OH⁺ line is blueshifted and peaks near the CO and continuum emission peak, while the emission is redshifted and peaks offset by 1.7 kpc from the CO and continuum emission peak, suggesting that the gas is associated with a massive molecular outflow from the intensely star-forming nucleus that supplies 125 M_⊙ yr⁻¹ of enriched gas to its halo.

Modeling of the NICER X-ray waveform of the pulsar PSR J0030+0451, aimed at constraining the neutron star mass and radius, has inferred surface hot spots (the magnetic polar caps) that imply significantly nondipolar magnetic fields. To this end, we investigate magnetic field configurations that comprise offset dipole-plus-quadrupole components using a static vacuum field and force-free global magnetosphere models. Taking into account the compactness and observer angle values provided by Miller et al. and Riley et al., we compute geodesics from the observer plane to the polar caps to compute the resulting X-ray light curve. We explore, through Markov Chain Monte Carlo techniques, the detailed magnetic field configurations that can reproduce the observed X-ray light curve and have discovered degeneracies, i.e., diverse field configurations, which can provide sufficient descriptions of the NICER X-ray waveforms. Having obtained the force-free field structures, we then compute the corresponding synchronous γ-ray light curves following Kalapotharakos et al.; these we compare to those obtained by Fermi-LAT, to provide models consistent with both the X-ray and the γ-ray data, thereby restricting further the multipole field parameters. An essential aspect of this approach is the proper computation of the relative phase between the synchronous X- and γ-ray light curves. We conclude with a discussion of the broader implications of our study.

Under the right conditions, the streaming instability between imperfectly coupled dust and gas is a powerful mechanism for planetesimal formation as it can concentrate dust grains to the point of gravitational collapse. In its simplest form, the streaming instability can be captured by analyzing the linear stability of unstratified disk models, which represent the midplane of protoplanetary disks. We extend such studies by carrying out vertically global linear stability analyses of dust layers in protoplanetary disks. We find that the dominant form of instability in stratified dust layers is the one driven by the vertical gradient in the rotation velocity of the dust−gas mixture, but also requires partial dust−gas coupling. These vertically shearing streaming instabilities grow on orbital timescales and occur on radial length scales  ∼ 10⁻³H_g, where H_g is the local pressure scale height. The classic streaming instability, associated with the relative radial drift between dust and gas, occurs on radial length scales  ∼ 10⁻²H_g, but has much smaller growth rates than vertically shearing streaming instabilities. Including gas viscosity is strongly stabilizing and leads to vertically elongated disturbances. We briefly discuss the potential effects of vertically shearing streaming instabilities on planetesimal formation.

The shape of bent, double-lobed radio sources requires a dense gaseous medium. Bent sources can therefore be used to identify galaxy clusters and characterize their evolutionary history. By combining radio observations from the Very Large Array Faint Images of the Radio Sky at Twenty centimeters (VLA FIRST) survey with optical and infrared imaging of 36 red sequence selected cluster candidates from the high-z Clusters Occupied by Bent Radio AGN (COBRA) survey (0.35 < z < 2.2), we find that radio sources with narrower opening angles reside in richer clusters, indicating that the cluster environment impacts radio morphology. Within these clusters, we determine 55.5% of our radio host galaxies are brightest cluster galaxies (BCGs) and that the remainder are associated with other luminous galaxies. The projected separations between the radio sources and cluster centers and the sizes of the opening angles of bent sources follow similar distributions for BCG and non-BCG host populations, suggesting that COBRA host galaxies are either BCGs or galaxies that may evolve into BCGs. By measuring the orientation of the radio sources relative to the cluster centers, we find between 30% and 42% of COBRA bent sources are outgoing and have passed through the cluster center, while between 8% and 58% of COBRA bent sources are infalling. Although these sources typically do not follow directly radial paths, the large population of outgoing sources contrasts what is observed in low-z samples of bent sources and may indicate that the intracluster medium is less dense in these high-z clusters.

Symplectic integrators that preserve the geometric structure of Hamiltonian flows and do not exhibit secular growth in energy errors are suitable for the long-term integration of N-body Hamiltonian systems in the solar system. However, the construction of explicit symplectic integrators is frequently difficult in general relativity because all variables are inseparable. Moreover, even if two analytically integrable splitting parts exist in a relativistic Hamiltonian, all analytical solutions are not explicit functions of proper time. Naturally, implicit symplectic integrators, such as the midpoint rule, are applicable to this case. In general, these integrators are numerically more expensive to solve than same-order explicit symplectic algorithms. To address this issue, we split the Hamiltonian of Schwarzschild spacetime geometry into four integrable parts with analytical solutions as explicit functions of proper time. In this manner, second- and fourth-order explicit symplectic integrators can be easily made available. The new algorithms are also useful for modeling the chaotic motion of charged particles around a black hole with an external magnetic field. They demonstrate excellent long-term performance in maintaining bounded Hamiltonian errors and saving computational cost when appropriate proper time steps are adopted.

The High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory continuously detects TeV photons and particles within its large field of view, accumulating every day a deeper exposure of two-thirds of the sky. We analyzed 1523 days of HAWC live data acquired over four and a half years, in a follow-up analysis of 138 nearby (z < 0.3) active galactic nuclei from the Third Catalog of Hard Fermi-LAT sources culminating within 40° of the zenith at Sierra Negra, the HAWC site. This search for persistent TeV emission used a maximum-likelihood analysis assuming intrinsic power-law spectra attenuated by pair production of gamma-ray photons with the extragalactic background light. HAWC clearly detects persistent emission from Mkn 421 and Mkn 501, the two brightest blazars in the TeV sky, at 65σ and 17σ level, respectively. Marginal evidence, just above the 3σ level, was found for three other known very high-energy emitters: the radio galaxy M87 and the BL Lac objects VER J0521+211 and 1ES 1215+303, the latter two at z ∼ 0.1. We find a 4.2σ evidence for collective emission from the set of 30 previously reported very high-energy sources, with Mkn 421 and Mkn 501 excluded. Upper limits are presented for the sample under the power-law assumption and in the predefined (0.5–2.0), (2.0–8.0), and (8.0–32.0) TeV energy intervals.

We apply the spectroscopy-based stellar-color regression (SCR) method to perform an accurate photometric recalibration of the second data release from the SkyMapper Southern Survey (SMSS DR2). From comparison with a sample of over 200,000 dwarf stars with stellar atmospheric parameters taken from GALAH+ DR3 and with accurate, homogeneous photometry from Gaia DR2, zero-point offsets are detected in the original photometric catalog of SMSS DR2, in particular for the gravity- and metallicity-sensitive uv bands. For the uv bands, the zero-point offsets are close to zero at very low extinction, and then steadily increase with E(B − V), reaching as large as 0.174 and 0.134 mag respectively, at E(B − V) ∼ 0.5 mag. These offsets largely arise from the adopted dust term in the transformations used by SMSS DR2 to construct photometric calibrators from the ATLAS reference catalog. For the gr bands, the zero-point offsets exhibit negligible variations with the E(B − V) of Schlegel et al. due to their tiny coefficients on the dust term in the transformation. Our study also reveals small but significant spatial variations of the zero-point offsets in all uvgr bands. External checks using Strömgren photometry, WD loci, and the SDSS Stripe 82 standard-star catalog independently confirm the zero-points found by our revised SCR method.

We report a comprehensive list of accurate Ritz wavelengths and calculated transition probabilities for parity-forbidden [Mn ii] lines. Ritz wavelengths have been derived from experimentally established energy level values resulting from an extensive analysis of a high-resolution Fourier-transform emission spectrum of singly ionized manganese. Our analysis includes transitions between all known metastable and other long-lived levels of Mn ii giving a total of 1130 [Mn ii] Ritz wavelengths. Our entire list of derived Ritz wavelengths for [Mn ii] lines ranges between 237 nm and 170 μm (42,125–58 cm⁻¹). The accurate Ritz wavelengths and calculated transition probabilities for forbidden lines in this paper are useful in the study and diagnostics of nebulae and other low-density astrophysical plasmas.

Nova Cas 2020 was a second example of a classical nova forming both C₂ and CN molecules during its near-maximum phase. The formation C₂ and CN is indicative of the carbon-rich (C/O > 1) gas envelope of the nova. Our low-resolution spectroscopic observations in the optical from UT 2020 July 31 to August 19 revealed the appearance and the disappearance of the molecular absorption bands of C₂ and CN in Nova Cas 2020. These molecules were present during ∼3 days only. Based on analysis of the C₂ Swan band profiles, C₂ (and probably CN also) formed at ∼5000 K in the nova envelope (see ∼8000 K for typical novae at their visual brightness maxima). Spectral evolution and the formation conditions of the molecules are similar to those of V2676 Oph, which is the first example of a C₂/CN-forming nova. We predict that a late-phase grain formation episode similar to that seen in V2676 Oph will occur in Nova Cas 2020.

We present results from our X-ray analysis of a systematic search for triple active galactic nuclei (AGNs) in nearby (z < 0.077) triple galaxy mergers. We analyze archival Chandra observations of seven triple galaxy mergers with baymax (Bayesian Analysis of Multiple AGNs in X-rays), fitting each observation with single, dual, and triple X-ray point-source models. In doing so, we conclude that one triple merger has one X-ray point source (SDSS J0858+1822, although it is unlikely to be an AGN), five triple mergers are likely composed of two X-ray point sources (NGC 3341, SDSS J1027+1749, SDSS J1631+2352, SDSS J1708+2153, and SDSS J2356−1016), and one system is composed of three X-ray point sources (SDSS J0849+1114). By fitting the individual X-ray spectra of each point source, we analyze the 2−7 keV luminosities, as well as the levels of obscuration associated with each potential AGN. We find that 4/5 dual X-ray point-source systems have primary and secondary point sources with bright X-ray luminosities (L_2−7kev > 10⁴⁰ erg s⁻¹), possibly associated with four new undetected dual AGNs. The dual and triple-point-source systems are found to have physical separations between 3 and 9 kpc and flux ratios between 2 × 10⁻³ and  0.84. A multiwavelength analysis to determine the origin of the X-ray point sources discovered in this work is presented in our companion paper (Foord et al. 2020c).

We present results from a multiwavelength analysis searching for multiple active galactic nucleus (AGN) systems in nearby (z < 0.077) triple galaxy mergers. Combining archival Chandra, Sloan Digital Data Survey (SDSS), Wide-field Infrared Survey Explorer (WISE), and Very Large Array observations, we quantify the rate of nearby triple AGNs, as well as investigate possible connections between supermassive black hole accretion and merger environments. Analyzing the multiwavelength observations of seven triple galaxy mergers, we find that one triple merger has a single AGN (NGC 3341); we discover, for the first time, four likely dual AGNs (SDSS J1027+1749, SDSS J1631+2352, SDSS J1708+2153, and SDSS J2356−1016); we confirm one triple-AGN system, SDSS J0849+1114; and one triple merger in our sample remains ambiguous (SDSS J0858+1822). Analyzing the WISE data, we find a trend of increasing N_H (associated with the primary AGN) as a function of increasing W1 – W2 color, reflecting that the motions of gas and dust are coupled in merging environments, where large amounts of both can be funneled into the active central region during mergers. Additionally, we find that the one triple-AGN system in our sample has the highest levels of N_H and W1 – W2 color, while the dual-AGN candidates all have lower levels; these results are consistent with theoretical merger simulations that suggest that higher levels of nuclear gas are more likely to activate AGNs in mergers.

Electron–positron pair creation near sub-Eddington accretion rate black holes is believed to be dominated by the Breit–Wheeler process (photon–photon collisions). The interacting high-energy photons are produced when unscreened electric fields accelerate leptons either in coherent, macroscopic gaps, or in incoherent structures embedded in the turbulent plasma flow. The latter type of acceleration results in a drizzle of pair production sourced by photons from the background radiation field whose energies are near the pair-production threshold. In this work, we use radiation general relativistic magnetohydrodynamic simulations to extend an earlier study of pair drizzle by Mościbrodzka et al. We focus on low-magnetization (standard and normal evolution) accretion onto supermassive Kerr black holes and consider radiation due to synchrotron, bremsstrahlung, and Compton upscattering processes. We confirm that pair drizzle in M87 is sufficient to keep the magnetospheric charge density orders of magnitude above the Goldreich–Julian density. We also find that pair production peaks along the jet–disk boundary.

We perform the first three-dimensional radiation hydrodynamical simulations that investigate the growth of intermediate-mass BHs (IMBHs) embedded in massive self-gravitating, dusty nuclear accretion disks. We explore the dependence of mass accretion efficiency on the gas metallicity Z and mass injection at super-Eddington accretion rates from the outer galactic disk ${\dot{M}}_{\mathrm{in}}$, and we find that the central BH can be fed at rates exceeding the Eddington rate only when the dusty disk becomes sufficiently optically thick to ionizing radiation. In this case, mass outflows from the disk owing to photoevaporation are suppressed, and thus a large fraction (≳40%) of the mass injection rate can feed the central BH. The conditions are expressed as ${\dot{M}}_{\mathrm{in}}\gt 2.2\times {10}^{-1}\,{\text{}}{M}_{\odot }$${\mathrm{yr}}^{-1}{(1+Z/{10}^{-2}{\text{}}{Z}_{\odot })}^{-1}({c}_{{\rm{s}}}/10$$\mathrm{km}\,{{\rm{s}}}^{-1})$, where c_s is the sound speed in the gaseous disk. With increasing numerical resolution, vigorous disk fragmentation reduces the disk surface density, and dynamical heating by formed clumps makes the disk geometrically thicker. As a result, the photoevaporative mass-loss rate rises and thus the critical injection rate increases for fixed metallicity. This process enables super-Eddington growth of BHs until the BH mass reaches ${M}_{\mathrm{BH}}\sim {10}^{7\mbox{--}8}\,{\text{}}{M}_{\odot }$, depending on the properties of the host dark-matter halo and metal-enrichment history. In the assembly of protogalaxies, seed BHs that form in overdense regions with a mass variance of 3–4σ at z ∼ 15–20 are able to undergo short periods of rapid growth and transit into the Eddington-limited growth phase afterward to be supermassive BHs observed at z > 6–7.

In this contribution, we achieve the primary goal of the active galactic nucleus (AGN) STORM campaign by recovering velocity–delay maps for the prominent broad emission lines (Lyα, C iv, He ii, and Hβ) in the spectrum of NGC 5548. These are the most detailed velocity–delay maps ever obtained for an AGN, providing unprecedented information on the geometry, ionization structure, and kinematics of the broad-line region. Virial envelopes enclosing the emission-line responses show that the reverberating gas is bound to the black hole. A stratified ionization structure is evident. The He ii response inside 5–10 lt-day has a broad single-peaked velocity profile. The Lyα, C iv, and Hβ responses extend from inside 2 to outside 20 lt-day, with double peaks at ±2500 km s⁻¹ in the 10–20 lt-day delay range. An incomplete ellipse in the velocity–delay plane is evident in Hβ. We interpret the maps in terms of a Keplerian disk with a well-defined outer rim at R = 20 lt-day. The far-side response is weaker than that from the near side. The line-center delay $\tau =(R/c)(1-\sin i)\approx 5$ days gives the inclination i ≈ 45°. The inferred black hole mass is M_BH ≈ 7 × 10⁷M_⊙. In addition to reverberations, the fit residuals confirm that emission-line fluxes are depressed during the "BLR Holiday" identified in previous work. Moreover, a helical "Barber-Pole" pattern, with stripes moving from red to blue across the C iv and Lyα line profiles, suggests azimuthal structure rotating with a 2 yr period that may represent precession or orbital motion of inner-disk structures casting shadows on the emission-line region farther out.

Liu and collaborators recently proposed an elliptical accretion disk model for tidal disruption events (TDEs). They showed that the accretion disks of optical/UV TDEs are large and highly eccentric and suggested that the broad optical emission lines with complex and diverse profiles originate in a cool eccentric accretion disk of random inclination and orientation. In this paper, we calculate the radiation efficiency of the elliptical accretion disk and investigate the implications for observations of TDEs. We compile observational data for the peak bolometric luminosity and total radiation energy after peak brightness of 18 TDE sources and compare these data to the predictions from the elliptical accretion disk model. Our results show that the observations are consistent with the theoretical predictions and that the majority of the orbital energy of the stellar debris is advected into the black hole (BH) without being converted into radiation. Furthermore, we derive the masses of the disrupted stars and the masses of the BHs of the TDEs. The BH masses obtained in this paper are also consistent with those calculated with the M_BH–σ_* relation. Our results provide an effective method for measuring the masses of BHs in large numbers of TDEs to be discovered in ongoing and next-generation sky surveys, regardless of whether the BHs are located at the centers of galactic nuclei or wander in disks and halos.

We present the afterglow light curves produced by the deceleration of a nonrelativistic ejecta mass in a stratified circumstellar medium with a density profile n(r) ∝ r^−k with k = 0, 1, 1.5, 2, and 2.5. Once the ejecta mass is launched with equivalent kinetic energy parameterized by E(>β) ∝ β^−α (where β is the ejecta velocity) and propagates into the surrounding circumstellar medium, it first moves with constant velocity (the free-coasting phase), and later it decelerates (the Sedov–Taylor expansion). We present the predicted synchrotron and synchrotron self-Compton light curves during the free-coasting phase and the subsequent Sedov–Taylor expansion. In particular cases, we show the corresponding light curves generated by the deceleration of several ejecta masses with different velocities launched during the coalescence of binary compact objects and the core collapse of dying massive stars, which will contribute at distinct timescales, frequencies, and intensities. Finally, using the multiwavelength observations and upper limits collected by a large campaign of orbiting satellites and ground telescopes, we constrain the parameter space of both the kilonova (KN) afterglow in GW170817 and the possibly generated KN afterglow in S190814bv. Further observations on timescales of years post-merger are needed to derive tighter constraints.

In this work, we report on observations with the Neutron Star Interior Composition Explorer of the known neutron star X-ray transient XTE J1739–285. We observed the source in 2020 February and March, finding it in a highly active bursting state. Across a 20 day period, we detected 32 thermonuclear X-ray bursts, with an average burst recurrence time of ${2.0}_{-0.3}^{+0.4}\,\mathrm{hr}$. A timing and spectral analysis of the ensemble of X-ray bursts reveals homogeneous burst properties, evidence for short-recurrence time bursts, and the detection of a 386.5 Hz burst oscillation candidate. The latter is especially notable, given that a previous study of this source claimed a 1122 Hz burst oscillation candidate. We did not find any evidence of variability near 1122 Hz and instead find that the 386.5 Hz oscillation is the more prominent signal of the two burst oscillation candidates. Hence, we conclude it is unlikely that XTE J1739–285 has a submillisecond rotation period.

Ring structures are observed through (sub)millimeter dust continuum emission in various circumstellar disks from the early stages of class 0 and I to the late stage of class II young stellar objects (YSOs). In this paper, we study one of the possible scenarios for such ring formation, which is the coagulation of dust aggregates in the early stage. The dust grains grow in an inside-out manner because the growth timescale is roughly proportional to the orbital period. The boundary of the dust evolution can be regarded as the growth front, where the growth time is comparable to the disk age. Using radiative transfer calculations based on the dust coagulation model, we find that the growth front can be observed as a ring structure because the dust surface density changes sharply at this position. Furthermore, we confirm that the observed ring positions in YSOs with an age of ≲1 Myr are consistent with the growth front. The growth front could be important in creating the ring structure in particular for the early stage of disk evolution, such as class 0 and I sources.

Recent observations have revealed the existence of multiple-planet systems composed of Earth-mass planets around late M dwarfs. Most of their orbits are close to commensurabilities, which suggests that planets were commonly trapped in resonant chains in their formation around low-mass stars. We investigate the formation of multiple-planet systems in resonant chains around low-mass stars. A time-evolution model of the multiple-planet formation via pebble accretion in the early phase of the disk evolution is constructed based on the formation model for the TRAPPIST-1 system by Ormel et al. Our simulations show that knowing the protoplanet appearance timescale is important for determining the number of planets and their trapped resonances: as the protoplanet appearance timescale increases, fewer planets are formed, which are trapped in more widely separated resonances. We find that there is a range of the protoplanet appearance timescale for forming stable multiple-planet systems in resonant chains. This range depends on the stellar mass and disk size. We suggest that the protoplanet appearance timescale is a key parameter for studying the formation of multiple-planet systems with planets in resonant chains around low-mass stars. The composition of the planets in our model is also discussed.

An optimal estimate for Stokes parameters is derived for the situation in X-ray astronomy where the instrument has a modulation factor that varies significantly with energy but the signals are very weak or mildly polarized. For such sources, the band of analysis may be broadened in order to obtain a significant polarization measurement. Optimal estimators are provided for the cases of binned and unbinned data and applied to data such as might be obtained for faint or weakly polarized sources observed using the Imaging X-ray Polarimetry Explorer. For a sample situation, the improvement in the minimum detectable polarization is 6%–7% using a count-weighted rms of the modulation factor, when compared to a count-weighted average. Improving the modulation factor, such as when using a neural network approach to Imaging X-ray Polarimetry Explorer event tracks, can provide additional improvement up to 10%–15%. The actual improvement depends on the spectral shape and the details of the instrument response functions.

Magnetohydrodynamical (MHD) dynamos emerge in many different astrophysical situations where turbulence is present, but the interaction between large-scale dynamos (LSDs) and small-scale dynamos (SSDs) is not fully understood. We performed a systematic study of turbulent dynamos driven by isotropic forcing in isothermal MHD with magnetic Prandtl number of unity, focusing on the exponential growth stage. Both helical and nonhelical forcing was employed to separate the effects of LSD and SSD in a periodic domain. Reynolds numbers (${\mathrm{Re}}_{{\rm{M}}}$) up to ≈250 were examined and multiple resolutions used for convergence checks. We ran our simulations with the Astaroth code, designed to accelerate 3D stencil computations on graphics processing units (GPUs) and to employ multiple GPUs with peer-to-peer communication. We observed a speedup of  ≈35 in single-node performance compared to the widely used multi-CPU MHD solver Pencil Code. We estimated the growth rates from both the averaged magnetic fields and their power spectra. At low ${\mathrm{Re}}_{{\rm{M}}}$ LSD growth dominates, but at high ${\mathrm{Re}}_{{\rm{M}}}$ SSD appears to dominate in both helically and nonhelically forced cases. Pure SSD growth rates follow a logarithmic scaling as a function of ${\mathrm{Re}}_{{\rm{M}}}$. Probability density functions of the magnetic field from the growth stage exhibit SSD behavior in helically forced cases even at intermediate ${\mathrm{Re}}_{{\rm{M}}}$. We estimated mean field turbulence transport coefficients using closures like the second-order correlation approximation (SOCA). They yield growth rates similar to the directly measured ones and provide evidence of α quenching. Our results are consistent with the SSD inhibiting the growth of the LSD at moderate ${\mathrm{Re}}_{{\rm{M}}}$, while the dynamo growth is enhanced at higher ${\mathrm{Re}}_{{\rm{M}}}$.

We present a catalog of high-velocity C ivλ1548,1551 mini-broad absorption lines (mini-BALs) in the archives of the Very Large Telescope-UV Visual Echelle Spectrograph and Keck-High Resolution Echelle Spectrometer. We identify C iv mini-BALs based on smooth rounded BAL-like profiles with velocity blueshifts <−4000 km s⁻¹ and widths in the range 70 ≲ FWHM(1548) ≲ 2000 km s⁻¹. We find 105 mini-BALs in 44 quasars from a total sample of 638 quasars. The fraction of quasars with at least one mini-BAL meeting our criteria is roughly ∼9% after correcting for incomplete velocity coverage. All of the systems are highly ionized based on the strong presence of N v and O vi and/or the absence of Si ii and C ii when within the wavelength coverage. Two of the mini-BAL systems in our catalog, plus three others at smaller velocity shifts, have P v λ1118,1128 absorption indicating highly saturated C iv absorption and total hydrogen column densities ≳10²² cm⁻². Most of the mini-BALs are confirmed to have optical depths ≳1 with partial covering of the quasar continuum source. The covering fractions are as small as 0.06 in C iv and 0.03 in Si iv, corresponding to outflow absorbing structures <0.002 pc across. When multiple lines are measured, the lines of less abundant ions tend to have narrower profiles and smaller covering fractions indicative of inhomogeneous absorbers where higher column densities occur in smaller clumps. This picture might extend to BAL outflows if the broader and generally deeper BALs form in either the largest clumps or collections of many mini-BAL-like clumps that blend together in observed quasar spectra.

We present the Stage II results from the ongoing Satellites Around Galactic Analogs (SAGA) Survey. Upon completion, the SAGA Survey will spectroscopically identify satellite galaxies brighter than M_r,o = −12.3 around 100 Milky Way (MW) analogs at z ∼ 0.01. In Stage II, we have more than quadrupled the sample size of Stage I, delivering results from 127 satellites around 36 MW analogs with an improved target selection strategy and deep photometric imaging catalogs from the Dark Energy Survey and the Legacy Surveys. We have obtained 25,372 galaxy redshifts, peaking around z = 0.2. These data significantly increase spectroscopic coverage for very low redshift objects in 17 < r_o < 20.75 around SAGA hosts, creating a unique data set that places the Local Group in a wider context. The number of confirmed satellites per system ranges from zero to nine and correlates with host galaxy and brightest satellite luminosities. We find that the number and luminosities of MW satellites are consistent with being drawn from the same underlying distribution as SAGA systems. The majority of confirmed SAGA satellites are star-forming, and the quenched fraction increases as satellite stellar mass and projected radius from the host galaxy decrease. Overall, the satellite quenched fraction among SAGA systems is lower than that in the Local Group. We compare the luminosity functions and radial distributions of SAGA satellites with theoretical predictions based on cold dark matter simulations and an empirical galaxy–halo connection model and find that the results are broadly in agreement.

Strongly driven magnetic reconnection occurs in astrophysical events and also in laboratory experiments with laser-produced plasma. We have performed 2.5D particle-in-cell simulations of collisions of two high-energy–density plasmas resulting in strongly driven magnetic reconnection that demonstrates significant non-thermal ion acceleration. Such acceleration is significant only when the plasma beta is sufficiently low that the Alfvén speed at the reconnection inflow exceeds the thermal speed. Under these conditions, the most energetic ions are primarily accelerated by the Hall electric field in the reconnection outflow, especially at the trailing edge of an emerging plasmoid in the outflow. Laboratory experiments in the near future should be able to confirm these predictions and their applicability to astrophysical situations.

A rapidly rotating and highly magnetized neutron star (NS) could be formed from explosive phenomena such as superluminous supernovae and gamma-ray bursts. This newborn NS can substantially influence the emission of these explosive transients through its spin-down. The spin-down evolution of the NS can sometimes be affected by fallback accretion, although it is usually regulated by the magnetic dipole radiation and gravitational wave radiation of the NS. Under appropriate conditions, the accreting material can be first ejected and subsequently recycled back, so that the accretion disk can remain in a quasi-steady state for a long time. Here we describe the interaction of the NS with such a propeller-recycling disk and their coevolution. Our result shows that the spin-down of the NS can be initially dominated by the propeller, which prevents the disk material from falling onto the NS until hundreds or thousands of seconds later. It is suggested that the abrupt fall of the disk material onto the NS could significantly suppress the magnetic dipole radiation and then convert the NS from a normal magnetar to a low-field magnetar. This evolution behavior of the newborn NS can help us understand the very different influence of the NS on the early GRB afterglows and the late supernova/kilonova emission.

We present 850 μm polarization observations of the L1689 molecular cloud, part of the nearby Ophiuchus molecular cloud complex, taken with the POL-2 polarimeter on the James Clerk Maxwell Telescope (JCMT). We observe three regions of L1689: the clump L1689N which houses the IRAS 16293-2433 protostellar system, the starless clump SMM-16, and the starless core L1689B. We use the Davis–Chandrasekhar–Fermi method to estimate plane-of-sky field strengths of 366 ± 55 μG in L1689N, 284 ± 34 μG in SMM-16, and 72 ± 33 μG in L1689B, for our fiducial value of dust opacity. These values indicate that all three regions are likely to be magnetically transcritical with sub-Alfvénic turbulence. In all three regions, the inferred mean magnetic field direction is approximately perpendicular to the local filament direction identified in Herschel Space Telescope observations. The core-scale field morphologies for L1689N and L1689B are consistent with the cloud-scale field morphology measured by the Planck Space Observatory, suggesting that material can flow freely from large to small scales for these sources. Based on these magnetic field measurements, we posit that accretion from the cloud onto L1689N and L1689B may be magnetically regulated. However, in SMM-16, the clump-scale field is nearly perpendicular to the field seen on cloud scales by Planck, suggesting that it may be unable to efficiently accrete further material from its surroundings.

Upcoming missions, including the James Webb Space Telescope, will soon characterize the atmospheres of terrestrial-type exoplanets in habitable zones around cool K- and M-type stars by searching for atmospheric biosignatures. Recent observations suggest that the ionizing radiation and particle environment from active cool planet hosts may be detrimental to exoplanetary habitability. Since no direct information on the radiation field is available, empirical relations between signatures of stellar activity, including the sizes and magnetic fields of starspots, are often used. Here, we revisit the empirical relation between the starspot size and the effective stellar temperature and evaluate its impact on estimates of stellar flare energies, coronal mass ejections, and fluxes of the associated stellar energetic particle events.

Quality metrics for Spitzer–Härm and Grad closures are presented based on the percentage of the heat flux moment supported only by nonnegative, physical, phase space densities ${\mathbb{F}}\gt 0$ underlying the closure. The Spitzer and Grad qualities exceed 95% for the perturbative regimes where Spitzer's formulation is analytically known to be convergent. Beyond this regime both heat flux qualities fall about 30% per decade increase of  > 0.01. In the solar corona the first decade's decrease in quality straddles the radius of the coronal temperature maximum and spans the initial acceleration of the solar wind. By the end of the second decade of increase of the observer is between 5 and 10R_⊙, already in conditions comparable to those at 1 au with ≃60% degradation of quality. These strong radial decays of closure quality show that integrating the fluid equations using such closures must represent a very poor assay of the role and effects of ∇ · q had the heat flux been described throughout with a uniformly high quality closure procedure. For small , $\,{\mathbb{F}}\lt 0$ occurs for cosine of pitch angle μ < 0 opposed to q at speeds above 2 thermal speeds and are omnipresent (but ignorable) for truly perturbative closures. Above a computed threshold in unphysical ${\mathbb{F}}\lt 0$ occurs for speeds below 2 thermal speeds with μ > 0. The present work graphically shows ${\mathbb{F}}\lt 0$ regimes becoming increasingly pervasive as increases, first crossing ≃4 thermal speeds at μ < 0 and then representing ever larger unphysical incursions within the needed velocity sphere required to accurately determine the heat flux.

The ultraviolet (UV) emission from the most numerous stars in the universe, M dwarfs, impacts the formation, chemistry, atmospheric stability, and surface habitability of their planets. We have analyzed the spectral evolution of UV emission from M0–M2.5 (0.3–0.6 M_⊙) stars as a function of age, rotation, and Rossby number using Hubble Space Telescope observations of Tucana-Horologium (40 Myr), Hyades (650 Myr), and field (2–9 Gyr) objects. The quiescent surface flux of their C ii, C iii, C iv, He ii, N v, Si iii, and Si iv emission lines, formed in the stellar transition region, remains elevated at a constant level for 240 ± 30 Myr before declining by 2.1 orders of magnitude to an age of 10 Gyr. The Mg ii and far-UV pseudocontinuum emission, formed in the stellar chromosphere, exhibits more gradual evolution with age, declining by 1.3 and 1.7 orders of magnitude, respectively. The youngest stars exhibit a scatter of 0.1 dex in far-UV line and pseudocontinuum flux attributable only to rotational modulation, long-term activity cycles, or an unknown source of variability. Saturation-decay fits to these data can predict an M0–M2.5 star's quiescent emission in UV lines and the far-UV pseudocontinuum with an accuracy of 0.2–0.3 dex, the most accurate means presently available. Predictions of UV emission will be useful for studying exoplanetary atmospheric evolution and the destruction and abiotic production of biologically relevant molecules and interpreting infrared and optical planetary spectra measured with observatories like the James Webb Space Telescope.

We study properties of neutrino transfer in a remnant of a neutron star merger, consisting of a massive neutron star and a surrounding torus. We perform numerical simulations of the neutrino transfer by solving the Boltzmann equation with momentum-space angles and energies of neutrinos for snapshots of the merger remnant having elongated shapes. The evaluation of the neutrino distributions in multiple dimensions enables us to provide detailed information on the angle and energy spectra and neutrino reaction rates. We demonstrate features of asymmetric neutrino fluxes from the deformed remnant and investigate the neutrino emission region by determining the neutrinosphere for each energy. We examine the emission and absorption of neutrinos to identify important ingredients of heating rates through neutrino irradiation. We show that the contributions of μ- and τ-type neutrinos are important for the heating in the region above the massive neutron star. We also examine the angle moments and the Eddington tensor calculated directly from the neutrino distribution functions and compare them with those obtained by a moment closure approach, which is often used in the study of neutrino-radiation hydrodynamics. We show that the components of the Eddington tensor have non-monotonic behaviors, and the approximation of the closure relation may become inaccurate for high-energy neutrinos, whose fluxes are highly aspherical due to the extended merger remnant.

Interstellar dust grain alignment causes polarization from UV to mm wavelengths, allowing the study of the geometry and strength of the magnetic field. Over the last couple of decades, observations and theory have led to the establishment of the radiative alignment torque mechanism as a leading candidate to explain the effect. With a quantitatively well constrained theory, polarization can be used not only to study the interstellar magnetic field, but also the dust and other environmental parameters. Photodissociation regions, with their intense, anisotropic radiation fields, consequent rapid H₂ formation, and high spatial density-contrast provide a rich environment for such studies. Here we discuss an expanded optical, NIR, and mm-wave study of the IC 63 nebula, showing strong H₂ formation-enhanced alignment and the first direct empirical evidence for disalignment due to gas–grain collisions using high-resolution HCO⁺(J = 1-0) observations. We find that a relative amount of polarization is marginally anticorrelated with column density of HCO⁺. However, separating the lines of sight of optical polarimetry into those behind, or in front of, a dense clump as seen from γ Cas, the distribution separates into two well defined sets, with data corresponding to "shaded" gas having a shallower slope. This is expected if the decrease in polarization is caused by collisions since collisional disalignment rate is proportional to ${R}_{C}\propto n\sqrt{T}$. Ratios of the best-fit slopes for the "illuminated" and "shaded" samples of lines of sight agrees, within the uncertainties, with the square root of the two-temperature H₂ excitation in the nebula seen by Thi et al.

We present the first linear-polarization mosaicked observations performed by the Atacama Large Millimeter/submillimeter Array (ALMA). We mapped the Orion-KLeinmann-Low (Orion-KL) nebula using super-sampled mosaics at 3.1 and 1.3 mm as part of the ALMA Extension and Optimization of Capabilities program. We derive the magnetic field morphology in the plane of the sky by assuming that dust grains are aligned with respect to the ambient magnetic field. At the center of the nebula, we find a quasi-radial magnetic field pattern that is aligned with the explosive CO outflow up to a radius of approximately 12'' (∼5000 au), beyond which the pattern smoothly transitions into a quasi-hourglass shape resembling the morphology seen in larger-scale observations by the James-Clerk-Maxwell Telescope (JCMT). We estimate an average magnetic field strength $\left\langle B\right\rangle =9.4$ mG and a total magnetic energy of 2 × 10⁴⁵ erg, which is three orders of magnitude less than the energy in the explosive CO outflow. We conclude that the field has been overwhelmed by the outflow and that a shock is propagating from the center of the nebula, where the shock front is seen in the magnetic field lines at a distance of ∼5000 au from the explosion center.

Using the TNG100 (100 Mpc)³ simulation of the IllustrisTNG project, we demonstrate a strong connection between the onset of star formation quenching and the stellar size of galaxies. We do so by tracking the evolutionary history of extended and normal-size galaxies selected at z = 2 with $\mathrm{log}({M}_{* }/{\text{}}{M}_{\odot })$$=\,10.2\mbox{--}11$ and stellar-half-mass-radii above and within 1σ of the stellar size–stellar mass relation, respectively. We match the stellar mass and star formation rate distributions of the two populations. By z = 1, only 36% of the extended massive galaxies have quenched, in contrast to a quenched fraction of 69% for the normal-size massive galaxies. We find that normal-size massive galaxies build up their central stellar mass without a significant increase in their stellar size between $z=2\mbox{--}4$, whereas the stellar size of the extended massive galaxies almost doubles in the same time. In IllustrisTNG, lower black hole masses and weaker kinetic-mode feedback appears to be responsible for the delayed quenching of star formation in the extended massive galaxies. We show that relatively gas-poor mergers may be responsible for the lower central stellar density and weaker supermassive black hole feedback in the extended massive galaxies.

We use the Panoramic Survey Telescope and Rapid Response System 1 Survey (Pan-STARRS1, PS1) data to extend the Sloan Digital Sky Survey (SDSS) Stripe 82 quasar light curves. Combining PS1 and SDSS light curves provides a 15 yr baseline for 9248 quasars—5 yr longer than prior studies that used only SDSS. We fit the light curves with the damped random walk (DRW) model—a statistical description of their variability. We correlate the resulting DRW model parameters: asymptotic variability amplitude SF_∞, and characteristic timescale τ, with quasar physical properties—black hole mass, bolometric luminosity, and redshift. Using simulated light curves, we find that a longer baseline allows us to better constrain the DRW parameters. After adding PS1 data, the variability amplitude is a stronger function of the black hole mass and has a weaker dependence on quasar luminosity. In addition, the characteristic timescale τ dependence on quasar luminosity is marginally weaker. We also make predictions for the fidelity of DRW model parameter retrieval when light curves will be further extended with Zwicky Transient Facility and Rubin Observatory Legacy Survey of Space and Time data. Finally, we show how updated DRW parameters offer an independent method of discovering changing-look quasar candidates (CLQSOs). The candidates are outliers in terms of differences in magnitude and scatter between the SDSS and PS1 segments. We identify 40 objects (35 newly reported) with a tenfold increase in the variability timescale between SDSS and SDSS–PS1 data due to a large change in brightness (over 0.5 mag)—characteristic for CLQSOs.

On 2020 February 24, during their third observing run ("O3"), the Laser Interferometer Gravitational-wave Observatory and Virgo Collaboration detected S200224ca: a candidate gravitational wave (GW) event produced by a binary black hole (BBH) merger. This event was one of the best-localized compact binary coalescences detected in O3 (with 50%/90% error regions of 13/72 deg²), and so the Neil Gehrels Swift Observatory performed rapid near-UV/X-ray follow-up observations. Swift-XRT and UVOT covered approximately 79.2% and 62.4% (respectively) of the GW error region, making S200224ca the BBH event most thoroughly followed-up in near-UV (u-band) and X-ray to date. No likely EM counterparts to the GW event were found by the Swift BAT, XRT, or UVOT, nor by other observatories. Here, we report on the results of our searches for an EM counterpart, both in the BAT data near the time of the merger, and in follow-up UVOT/XRT observations. We also discuss the upper limits we can place on EM radiation from S200224ca, as well as the implications these limits have on the physics of BBH mergers. Namely, we place a shallow upper limit on the dimensionless BH charge, $\hat{q}\lt 1.4\times {10}^{-4}$, and an upper limit on the isotropic-equivalent energy of a blast wave E < 4.1 × 10⁵¹ erg (assuming typical GRB parameters).

Lanthanide element signatures are key to understanding many astrophysical observables, from merger kilonova light curves to stellar and solar abundances. To learn about the lanthanide element synthesis that enriched our solar system, we apply the statistical method of Markov Chain Monte Carlo to examine the nuclear masses capable of forming the r-process rare-earth abundance peak. We describe the physical constraints we implement with this statistical approach and demonstrate the use of the parallel chains method to explore the multidimensional parameter space. We apply our procedure to three moderately neutron-rich astrophysical outflows with distinct types of r-process dynamics. We show that the mass solutions found are dependent on outflow conditions and are related to the r-process path. We describe in detail the mechanism behind peak formation in each case. We then compare our mass predictions for neutron-rich neodymium and samarium isotopes to the latest experimental data from the CPT at CARIBU. We find our mass predictions given outflows that undergo an extended (n,γ)⇄(γ,n) equilibrium to be those most compatible with both observational solar abundances and neutron-rich mass measurements.

Interaction-powered supernovae (SNe) explode within an optically thick circumstellar medium (CSM) that could be ejected during eruptive events. To identify and characterize such pre-explosion outbursts, we produce forced-photometry light curves for 196 interacting SNe, mostly of Type IIn, detected by the Zwicky Transient Facility between early 2018 and 2020 June. Extensive tests demonstrate that we only expect a few false detections among the 70,000 analyzed pre-explosion images after applying quality cuts and bias corrections. We detect precursor eruptions prior to 18 Type IIn SNe and prior to the Type Ibn SN 2019uo. Precursors become brighter and more frequent in the last months before the SN and month-long outbursts brighter than magnitude −13 occur prior to 25% (5–69%, 95% confidence range) of all Type IIn SNe within the final three months before the explosion. With radiative energies of up to 10⁴⁹ erg, precursors could eject  ∼1 M_⊙ of material. Nevertheless, SNe with detected precursors are not significantly more luminous than other SNe IIn, and the characteristic narrow hydrogen lines in their spectra typically originate from earlier, undetected mass-loss events. The long precursor durations require ongoing energy injection, and they could, for example, be powered by interaction or by a continuum-driven wind. Instabilities during the neon- and oxygen-burning phases are predicted to launch precursors in the final years to months before the explosion; however, the brightest precursor is 100 times more energetic than anticipated.

We present a machine learning (ML) pipeline to identify star clusters in the multicolor images of nearby galaxies, from observations obtained with the Hubble Space Telescope as part of the Treasury Project LEGUS (Legacy ExtraGalactic Ultraviolet Survey). StarcNet (STAR Cluster classification NETwork) is a multiscale convolutional neural network (CNN) that achieves an accuracy of 68.6% (four classes)/86.0% (two classes: cluster/noncluster) for star cluster classification in the images of the LEGUS galaxies, nearly matching human expert performance. We test the performance of StarcNet by applying a pre-trained CNN model to galaxies not included in the training set, finding accuracies similar to the reference one. We test the effect of StarcNet predictions on the inferred cluster properties by comparing multicolor luminosity functions and mass–age plots from catalogs produced by StarcNet and by human labeling; distributions in luminosity, color, and physical characteristics of star clusters are similar for the human and ML classified samples. There are two advantages to the ML approach: (1) reproducibility of the classifications: the ML algorithm's biases are fixed and can be measured for subsequent analysis; and (2) speed of classification: the algorithm requires minutes for tasks that humans require weeks to months to perform. By achieving comparable accuracy to human classifiers, StarcNet will enable extending classifications to a larger number of candidate samples than currently available, thus increasing significantly the statistics for cluster studies.

We improve the identification and isolation of individual stellar populations in the Galactic halo based on an updated set of empirically calibrated stellar isochrones in the Sloan Digital Sky Survey and Pan-STARRS 1 photometric systems. Along the Galactic prime meridian (l = 0° and 180°), where proper motions and parallaxes from Gaia DR2 can be used to compute rotational velocities of stars in the rest frame of the Milky Way, we use the observed double color–magnitude sequences of stars having large transverse motions, which are mostly attributed to groups of stars in the metal-poor halo and the thick disk with halo-like kinematics, respectively. The Gaia sequences directly constrain color–magnitude relations of model colors, and help to improve our previous calibration using Galactic star clusters. Based on these updated sets of stellar isochrones, we confirm earlier results on the presence of distinct groups of stars in the metallicity versus rotational-velocity plane, and find that the distribution of the most metal-poor ([Fe/H] < −2) stars in our sample can be modeled using two separate groups on prograde and retrograde orbits, respectively. At 4–6 kpc from the Galactic plane, we find approximately equal proportions of the Splashed Disk, and the metal-rich (〈[Fe/H]〉 ∼ −1.6) and metal-poor (〈[Fe/H]〉 ∼ −2.5) halos on prograde orbits. The Gaia–Sausage–Enceladus, the metal-weak thick disk, and the retrograde halo structure(s) (〈[Fe/H]〉 ∼ −2.2) constitute approximately 10% of the rest of the stellar populations at these distances.

The fluting instability has been suggested as the driver of the subsurface structure of sunspot flux tubes. We conducted a series of numerical experiments where we used flux tubes with different initial curvatures to study the effect of the fluting instability on the subsurface structure of spots. We used the MURaM code, which has previously been used to simulate complete sunspots, to first compute four sunspots in the slab geometry and then two complete circular spots of opposite polarities. We find that the curvature of a flux tube indeed determines the degree of fluting the flux tube will undergo—the more curved a flux tube is, the more fluted it becomes. In addition, sunspots with strong curvature have strong horizontal fields at the surface and therefore readily form penumbral filaments. The fluted sunspots eventually break up from below, with lightbridges appearing at the surface several hours after fluting commences.

We present the discovery of a low-redshift damped Lyα (DLA) system in the spectrum of background starburst galaxy SDSS J111323.88+293039.3 (z = 0.17514). The DLA is at an impact parameter of ρ = 36 kpc from the star-forming galaxy, SDSS J111324.08+293051.2 (z = 0.17077). We measure an H i  column density of N(H i) = 3.47 × 10²⁰ cm⁻² along with multiple low-ionization species such as N i, N ii, Si ii, C ii, and Si iii. We also make an estimate of the covering fraction to be 0.883, giving us a limiting size of the DLA to be A_DLA ≥ 3.3 kpc². Assuming a uniform column density over the entire DLA system, we estimate its mass to be M_DLA ≥ 5.3 × 10⁶M_⊙. The extended illuminator and the low redshift of this DLA give us the unique opportunity to characterize its nature and the connection to its host galaxy. We measure a velocity offset of +131 km s⁻¹ from the systemic velocity of the host for the DLA. This velocity is −84 km s⁻¹ from the projected rotation velocity of the host galaxy as measured using a newly constructed rotation curve. Based on the size of the host galaxy, the H i  column density, and the gas kinematics, we believe this DLA is tracing the warm neutral gas in the H i  disk of the foreground galaxy. Our detection adds to a small set of low-redshift DLAs that have confirmed host galaxies, and is the first to be found using an extended background source.

The Stingray Nebula, a.k.a. Hen3-1357, appeared for the first time in 1990 when bright nebular lines and radio emission that had not been observed before were unexpectedly discovered. In the ensuing years, the nebula faded precipitously. We report changes in shape and large decreases in its nebular emission-line fluxes based on well-calibrated images obtained by the Hubble Space Telescope in 1996 and 2016. Hen3-1357 is now a "recombination nebula."

Blazar variability may be driven by stochastic processes. On the other hand, quasi-periodic oscillation (QPO) behaviors were recently reported to be detected in the Fermi-LAT data of blazars. However, the significances of these QPO signals given by traditional Fourier-like methods are still questioned. We analyze γ-ray light curves of the QPO blazars with two Gaussian process methods, CARMA and celerite, to examine the appropriateness of Gaussian processes for characterizing γ-ray light curves of blazars and the existence of the reported QPOs. We collect a sample of 27 blazars with possible γ-ray periodicity and generate their ∼11 yr Fermi-LAT light curves. We apply the Gaussian process models to the γ-ray light curves, and build their intrinsic power spectral densities (PSDs). The results show that in general the γ-ray light curves can be characterized by CARMA and celerite models, indicating that γ-ray variabilities of blazars are essentially Gaussian processes. The resulting PSDs are generally the red noise shapes with slopes between −0.6 and −1.7. Possible evidence for the γ-ray QPOs in PKS 0537−441 and PG 1553+113 are found in the Gaussian process modelings.

We report SOFIA/GREAT observations of high-J CO lines and [C ii] observations of the super star cluster candidate H72.97-69.39 in the Large Magellanic Cloud (LMC), which is in its very early formation stage. We use our observations to determine if shocks are heating the gas or if photon-dominated regions (PDRs) are being heated by local far-UV radiation. We use a PDR model and a shock model to determine whether the CO and [C ii] lines arise from PDRs or shocks. We can reproduce the observed high-J CO and [C ii] emission with a clumpy PDR model with the following properties: a density of 10^4.7 cm⁻³, a mass of 10⁴M_⊙, and UV radiation of 10^3.5 in units of Draine field. Comparison with the ALMA beam-filling factor suggests a higher density within the uncertainty of the fit. We find the lower-limit [C ii]/total infrared (TIR) ratio () traced by [C ii]/TIR to be 0.026%, lower than other known young star-forming regions in the LMC. Our shock models may explain the CO (16−15) and CO (11−10) emission lines with shock velocity of 8–11 km s⁻¹, pre-shock density of 10⁴–10⁵ cm⁻³, and G_UV = 0 in units of Draine field. However, the [C ii] line emission cannot be explained by a shock model, thus it is originating in a different gas component. Observations of [O i] 63 μm predicted to be 1.1 × 10⁻¹³ W m⁻² by PDR models and 7.8 × 10⁻¹⁵ W m⁻² by shock models will help distinguish between the PDR and shock scenarios.

We present the reheating constraints on an inflationary universe induced by perfect fluid models. Starting with the descriptions for the observables of the scalar field inflationary models in the reconstructed methods, we outline the procedure of perfect fluid inflationary models through these methods to calculate the inflationary observables and reheating. We show that the reheating e-folds number N_re and the reheating final temperature T_re are bound depending on the finite range of reasonable values of ${\omega }_{{re}}$. By restricting the equation-of-state parameter in the reheating stage, $-\tfrac{1}{3}\lt {\omega }_{{re}}\lt 1$, more stringent constraints can be derived for the model's parameter space of perfect fluid. These constraints correspond to viable values of the scalar spectral index n_s and tensor-to-scalar ratio r, released by Planck2018 observational data.

G31.41+0.31 is a well known chemically rich hot molecular core (HMC). Using Band 3 observations from the Atacama Large Millimeter Array (ALMA), we have analyzed the chemical and physical properties of the source. We have identified methyl isocyanate (CH₃NCO), a precursor of prebiotic molecules, toward the source. In addition to this, we have reported the presence of complex organic molecules (COMs) like methanol (CH₃OH), methanethiol (CH₃SH), and methyl formate (CH₃OCHO). Additionally, we have used transitions from molecules like HCN, H¹³CO⁺, and SiO to trace the presence of infall and outflow signatures around the star-forming region. For the COMs, we have estimated the column densities and kinetic temperatures, assuming molecular excitation under local thermodynamic equilibrium (LTE) conditions. From the estimated kinetic temperatures of certain COMs, we found that multiple temperature components may be present in the HMC environment. Comparing the obtained molecular column densities between the existing observational results around other HMCs, it seems that the COMs are favorably produced in the hot core environment (∼100 K or higher). Though the spectral emissions toward G31.41+0.31 are not fully resolved, we find that CH₃NCO and other COMs are possibly formed on grain/ice phase and populate the gas environment similar to other hot cores like Sgr B2, Orion KL, and G10.47+0.03.

We have developed a model of early X-ray afterglows of gamma-ray bursts originating from the reverse shock (RS) propagating through ultrarelativistic, highly magnetized pulsar-like winds produced by long-lasting central engines. We first performed fluid and magnetohydrodynamic numerical simulations of relativistic double explosions. We demonstrate that even for constant properties of the wind a variety of temporal behaviors can be produced, depending on the energy of the initial explosion and the wind power, the delay time for the switch-on of the wind, and the magnetization of the wind. X-ray emission of the highly magnetized RS occurs in the fast-cooling regime—this ensures high radiative efficiency and allows fast intensity variations. We demonstrate that (i) RS emission naturally produces light curves, showing power-law temporal evolution with various temporal indices; (ii) mild wind power, of the order of ∼10⁴⁶ erg s⁻¹ (equivalent isotropic), can reproduce the afterglows' plateau phase; (iii) termination of the wind can produce sudden steep decays; and (iv) short-duration afterglow flares are due to mild variations in the wind luminosity, with small total injected energy.

In this paper, we study the impact of different galaxy statistics and empirical metallicity scaling relations on the merging rates and properties of compact object binaries. Firstly, we analyze the similarities and differences of using the star formation rate functions versus stellar mass functions as galaxy statistics for the computation of cosmic star formation rate density. We then investigate the effects of adopting the Fundamental Metallicity Relation versus a classic Mass Metallicity Relation to assign metallicity to galaxies with given properties. We find that when the Fundamental Metallicity Relation is exploited, the bulk of the star formation occurs at relatively high metallicities, even at high redshift; the opposite holds when the Mass Metallicity Relation is employed, since in this case the metallicity at which most of the star formation takes place strongly decreases with redshift. We discuss the various reasons and possible biases giving rise to this discrepancy. Finally, we show the impact of these different astrophysical prescriptions on the merging rates and properties of compact object binaries; specifically, we present results for the redshift-dependent merging rates and for the chirp mass and time delay distributions of the merging binaries.

Since the discovery of FRB 200428 associated with the Galactic SGR 1935+2154, magnetars have been considered to power fast radio bursts (FRBs). It is widely believed that magnetars could form by core-collapse (CC) explosions and compact binary mergers, such as binary neutron stars (BNSs), binary white dwarfs (BWDs), and neutron star–white dwarf (NSWD) mergers. Therefore, it is important to distinguish the various progenitors. The expansion of the merger ejecta produces a time-evolving dispersion measure (DM) and rotation measure (RM) that can probe the local environments of FRBs. In this paper, we derive the scaling laws for the DM and RM from ejecta with different dynamical structures (the mass and energy distribution) in the uniform ambient medium (merger scenario) and wind environment (CC scenario). We find that the DM and RM will increase in the early phase, while DM will continue to grow slowly but RM will decrease in the later phase in the merger scenario. We fit the DM and RM evolution of FRB 121102 simultaneously for the first time in the BNS merger scenario and find that the source age is ∼9–10 yr when it was first detected in 2012, and the ambient medium density is ∼2.5–3.1 cm⁻³. The large offsets of some FRBs are consistent with the BNS/NSWD channel. The population synthesis method is used to estimate the rate of compact binary mergers. The rate of BWD mergers is close to the observed FRB rate. Therefore, the progenitors of FRBs may not be unique.

The local determination of the Hubble constant sits at a crossroad. Current estimates of the local expansion rate of the universe differ by about 1.7σ, derived from the Cepheid- and TRGB-based calibrations, applied to Type Ia supernovae. To help elucidate possible sources of systematic error causing the tension, we show in this study the recently developed distance indicator, the J-region Asymptotic Giant Branch (JAGB) method, can serve as an independent cross-check and comparison with other local distance indicators. Furthermore, we make the case that the JAGB method has substantial potential as an independent, precise, and accurate calibrator of Type Ia supernovae for the determination of H₀. Using the Local Group galaxy Wolf–Lundmark–Melotte (WLM), we present distance comparisons between the JAGB method, a TRGB measurement at near-infrared (JHK) wavelengths, a TRGB measurement in the optical I band, and a multiwavelength Cepheid period–luminosity relation determination. We find

$\begin{eqnarray*}\begin{array}{rcl}{\mu }_{0}\,(\mathrm{JAGB}) & = & 24.97\pm 0.02\ (\mathrm{stat})\pm 0.04\ (\mathrm{sys})\ \mathrm{mag}\\ {\mu }_{0}\,({\mathrm{TRGB}}_{\mathrm{NIR}}) & = & 24.98\pm 0.04\ (\mathrm{stat})\pm 0.07\ (\mathrm{sys})\ \mathrm{mag}\\ {\mu }_{0}\,({\mathrm{TRGB}}_{{\rm{F}}814{\rm{W}}}) & = & 24.93\pm 0.02\ (\mathrm{stat})\pm 0.06\ (\mathrm{sys})\ \mathrm{mag}\\ {\mu }_{0}\,(\mathrm{Cepheids}) & = & 24.98\pm 0.03\ (\mathrm{stat})\pm 0.04\ (\mathrm{sys})\ \mathrm{mag}.\end{array}\end{eqnarray*}$

All four methods are in good agreement, confirming the local self-consistency of the four distance scales at the 3% level and adding confidence that the JAGB method is as accurate and as precise a distance indicator as either of the other three astrophysically based methods.

We study the propagation of a Newtonian shock in a spherically symmetric, homologously expanding ejecta. We focus on media with a steep power-law density profile of the form ρ ∝ t⁻³v^−α, with α > 5, where v is the velocity of the expanding medium and t is time. Such profiles are expected in the leading edge of supernovae ejecta and sub-relativistic outflows from binary neutron star mergers. We find that such shocks always accelerate in the lab frame and lose causal contact with the bulk of the driver gas, owing to the steep density profile. However, the prolonged shock evolution exhibits two distinct pathways: In one, the shock strength diminishes with time until the shock eventually dies out. In the other, the shock strength steadily increases, and the solution approaches the self-similar solution that a shock is a static medium. By mapping the parameter space of shock solutions, we find that the evolutionary pathways are dictated by α and by the initial ratio between the shock velocity and the local upstream velocity. We find that for α < ω_c (ω_c ≈ 8), the shock always decays, and that for α > ω_c, the shock may decay or grow stronger depending on the initial value of the velocity ratio. These two branches bifurcate from a self-similar solution derived analytically for a constant velocity ratio. We analyze properties of the solutions that may have an impact on the observational signatures of such systems, and assess the conditions required for decaying shocks to break out from a finite medium.

Star formation and quenching are two of the most important processes in galaxy formation and evolution. We explore in the local universe the interrelationships among key integrated galaxy properties, including stellar mass M_*, star formation rate (SFR), specific SFR (sSFR), molecular gas mass ${M}_{{{\rm{H}}}_{2}}$, star formation efficiency (SFE) of the molecular gas, and the molecular gas to stellar mass ratio μ. We aim to identify the most fundamental scaling relations among these key galaxy properties and their interrelationships. We show that the integrated ${M}_{{{\rm{H}}}_{2}}$–SFR, SFR–M_*, and ${M}_{{{\rm{H}}}_{2}}$–M_* relations can be simply transformed from the μ–sSFR, SFE–μ, and SFE–sSFR relations, respectively. The transformation, in principle, can increase or decrease the scatter of each relation. Interestingly, we find that the latter three relations all have significantly smaller scatter than the corresponding former three. We show that the probability to achieve the observed small scatter by accident is extremely close to zero. This suggests that the smaller scatters of the latter three relations are driven by a more universal physical connection among these quantities. We then show that the large scatters in the former relations are due to their systematic dependence on other galaxy properties, and on the star formation and quenching process. We propose the sSFR–μ–SFE relation as the fundamental formation relation (FFR), which governs the star formation and quenching process and provides a simple framework to study galaxy evolution. Other scaling relations, including the integrated Kennicutt–Schmidt law, star-forming main sequence, and molecular gas main sequence, can all be derived from the FFR.

We report a study of X-ray emission from the white dwarf/M-type star binary system AR Scorpii using archival data taken in 2016–2020. It has been known that the X-ray emission is dominated by optically thin thermal plasma emission and its flux level varies significantly over the orbital phase. The X-ray emission also contains a component that modulates with the beat frequency between the white dwarf's spin frequency and orbital frequency. In this new analysis, the 2020 data taken by NICER shows that the X-ray emission modulates with the spin frequency as well as with the beat frequency, indicating that part of the X-ray emission comes from the white dwarf's magnetosphere. It is found that the signal of the spin frequency appears only at a specific orbital phase, while the beat signal appears over the orbital phase. We interpret the X-ray emission modulating with the spin frequency and the beat frequency as a result of synchrotron emission from electrons with smaller and larger pitch angles, respectively. In the long-term evolution, the beat pulse profile averaged over the orbital phase changes from a single-peak structure in 2016/2018 to a double-peak structure in 2020. The observed X-ray flux levels measured in 2016/2017 are higher than those measured in 2018/2020. The plasma temperature and the amplitude of the orbital waveform might vary with time too. These results indicate that the X-ray emission from AR Scorpii evolves on a timescale of years. This long-term evolution would be explained by a superorbital modulation related to, for example, a precession of the white dwarf or a fluctuation of the system related to the activity of the companion star.

The Sun has been found to be depleted in refractory (rock-forming) elements relative to nearby solar analogs, suggesting a potential indicator of planet formation. Given the small amplitude of the depletion, previous analyses have primarily relied on high signal-to-noise stellar spectra and a strictly differential approach to determine elemental abundances. We present an alternative, likelihood-based approach that can be applied to much larger samples of stars with lower precision abundance determinations. We utilize measurements of about 1700 solar analogs from the Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) and the APOGEE Stellar Parameter and Chemical Abundance Pipeline (ASPCAP DR16). By developing a hierarchical mixture model for the data, we place constraints on the statistical properties of the elemental abundances, including correlations with condensation temperature and the fraction of stars with refractory element depletions. We find evidence for two distinct populations: a depleted population of stars that makes up the majority of solar analogs including the Sun, and a not-depleted population that makes up between ∼10% and 30% of our sample. We find correlations with condensation temperature generally in agreement with higher precision surveys of a smaller sample of stars. Such trends, if robustly linked to the formation of planetary systems, provide a means to connect stellar chemical abundance patterns to planetary systems over large samples of Milky Way stars.

Cutoff energy in a synchrotron radiation spectrum of a supernova remnant (SNR) contains a key parameter of ongoing particle acceleration. We systematically analyze 11 young SNRs, including all historical SNRs, to measure the cutoff energy, thus shedding light on the nature of particle acceleration at the early stage of SNR evolution. The nonthermal (synchrotron) dominated spectra in filament-like outer rims are selectively extracted and used for spectral fitting because our model assumes that accelerated electrons are concentrated in the vicinity of the shock front owing to synchrotron cooling. The cutoff energy parameter (ε₀) and shock speed (v_sh) are related as ${\varepsilon }_{0}\propto {v}_{\mathrm{sh}}^{2}{\eta }^{-1}$ with a Bohm factor of η. Five SNRs provide us with spatially resolved ε₀–v_sh plots across the remnants, indicating a variety of particle acceleration. With all SNRs considered together, the systematic tendency of η clarifies a correlation between η and an age of t (or an expansion parameter of m) as η ∝ t^−0.4 (η ∝ m⁴). This might be interpreted as the magnetic field becomes more turbulent and self-generated, as particles are accelerated at a greater rate with time. The maximum energy achieved in SNRs can be higher if we consider the newly observed time dependence on η.

Historical sunspot drawings are very important resources for understanding past solar activity. We generate solar magnetograms and EUV images from Galileo sunspot drawings using a deep learning model based on conditional generative adversarial networks. We train the model using pairs of sunspot drawings from the Mount Wilson Observatory and their corresponding magnetograms (or UV/EUV images) from 2011 to 2015 except for every June and December by the Solar Dynamic Observatory satellite. We evaluate the model by comparing pairs of actual magnetograms (or UV/EUV images) and the corresponding AI-generated ones in June and December. Our results show that bipolar structures of the AI-generated magnetograms are consistent with those of the original ones and their unsigned magnetic fluxes (or intensities) are consistent with those of the original ones. Applying this model to the Galileo sunspot drawings in 1612, we generate Helioseismic and Magnetic Imager-like magnetograms and Atmospheric Imaging Assembly-like EUV images of the sunspots. We hope that the EUV intensities can be used for estimating solar EUV irradiance at long-term historical times.

We establish that there are two velocity systems along lines of sight that contribute to the emission-line spectrum of the brightest parts of the Orion Nebula. These overlie the Orion-S embedded molecular cloud southwest of the dominant ionizing star (θ¹ Ori C). Examination of 10 × 10'' samples of high spectral resolution emission-line spectra of this region reveals it to be of low ionization, with velocities and ionization different from the central part of the nebula. These properties jeopardize earlier determinations of abundance and physical conditions since they indicate that this region is much more complex than has been assumed in analyzing earlier spectroscopic studies and argue for use of very high spectral resolution or known simple regions in future studies.

We use the two-components bipolar toy model of core collapse supernova (CCSN) ejecta to fit the rapid decline from maximum luminosity in the light curve of the type IIb CCSN SN 2018gk (ASASSN-18am). In this toy model we use a template light curve from a different CCSN that is similar to SN 2018gk, but that has no rapid drop in its light curve. The bipolar morphology that we model with a polar ejecta and an equatorial ejecta increases the maximum luminosity and causes a steeper decline for an equatorial observer, relative to a similar spherical explosion. The total energy and mass of our toy model for SN 2018gk are ${E}_{\mathrm{SN}}=5\times {10}^{51}\,\mathrm{erg}$ and ${M}_{\mathrm{SN}}=2.7{M}_{\odot }$. This explosion energy is more than what a neutrino driven explosion mechanism can supply, implying that jets exploded SN 2018gk. These energetic jets likely shaped the ejecta to a bipolar morphology, as our toy model requires. We crudely estimate that f ≈ 2%–5% of all CCSNe show this behavior, most being hydrogen deficient (stripped-envelope) CCSNe, as we observe them from the equatorial plane. We estimate the overall fraction of CCSNe that have a pronounced bipolar morphology to be f_bip ≈ 5%–15% of all CCSNe.

Gamma-ray bursts (GRBs) detected at high redshift can be used to trace the Hubble diagram of the universe. However, the distance calibration of GRBs is not as easy as that of SNe Ia. For the calibration method based on the empirical luminosity correlations, there is an underlying assumption that the correlations should be universal over the whole redshift range. In this paper, we investigate the possible redshift dependence of six luminosity correlations with a completely model-independent deep-learning method. We construct a network combining the recurrent neural networks (RNN) and the Bayesian neural networks (BNN), where RNN is used to reconstruct the distance–redshift relation by training the network with the Pantheon compilation, and BNN is used to calculate the uncertainty of the reconstruction. Using the reconstructed distance–redshift relation of Pantheon, we test the redshift dependence of six luminosity correlations by dividing the full GRB sample into two subsamples (low-z and high-z subsamples), and find that only the E_p − E_γ relation has no evidence for redshift dependence. We use the E_p − E_γ relation to calibrate GRBs, and the calibrated GRBs give tight constraints on the flat ΛCDM model, with the best-fitting parameter ${{\rm{\Omega }}}_{{\rm{M}}}={0.307}_{-0.073}^{+0.065}$.

We report the discovery of a 10 comoving megaparsec (cMpc)-scale structure traced by massive submillimeter galaxies (SMGs) at z ∼ 4.6. These galaxies are selected from an emission line search of ALMA Band 7 observations targeting 184 luminous submillimeter sources (S_850μm ≥ 6.2 mJy) across 1.6 degrees² in the COSMOS field. We identify four [C ii] emitting SMGs and two probable [C ii] emitting SMG candidates at z = 4.60–4.64 with velocity-integrated signal-to-noise ratio of S/N > 8. Four of the six emitters are near-infrared blank SMGs. After excluding one SMG whose emission line is falling at the edge of the spectral window, all galaxies show clear velocity gradients along the major axes that are consistent with rotating gas disks. The estimated rotation velocities of the disks are 330–550 km s⁻¹ and the inferred host dark-matter halo masses are ∼2–8 × 10¹²M_⊙. From their estimated halo masses and [C ii] luminosity function, we suggest that these galaxies have a high (50%–100%) duty cycle and high (∼0.1) baryon conversion efficiency (SFR relative to baryon accretion rate), and that they contribute ≃2% to the total star formation rate density at z = 4.6. These SMGs are concentrated within just 0.3% of the full survey volume, suggesting they are strongly clustered. The extent of this structure and the individual halo masses suggest that these SMGs will likely evolve into members of a ∼10¹⁵M_⊙ cluster at z = 0. This survey reveals a synchronized dusty starburst in massive halos at z > 4, which could be driven by mergers or fed by smooth gas accretion.

Observation has not yet determined whether the distribution of spin vectors of galaxies is truly random. It is unclear whether is there any large-scale symmetry-breaking in the distribution of the vorticity field in the universe. Here, we present a formulation to evaluate the dipole component D_max of the observed spin distribution, whose statistical significance σ_D can be calibrated by the expected amplitude for 3D random walk (random flight) simulations. We apply this formulation to evaluate the dipole component in the distribution of Sloan Digital Sky Survey (SDSS) spirals. Shamir published a catalog of spiral galaxies from the SDSS DR8, classifying them with his pattern recognition tool into clockwise and counterclockwise (Z-spiral and S-spiral, respectively). He found significant photometric asymmetry in their distribution. We have confirmed that this sample provides dipole asymmetry up to a level of σ_D = 4.00. However, we also found that the catalog contains a significant number of multiple entries of the same galaxies. After removing the duplicated entries, the number of samples shrunk considerably to 45%. The actual dipole asymmetry observed for the "cleaned" catalog is quite modest, σ_D = 0.29. We conclude that SDSS data alone do not support the presence of a large-scale symmetry-breaking in the spin vector distribution of galaxies in the local universe. The data are compatible with a random distribution.

We measure the genus of the galaxy distribution in two-dimensional slices of the SDSS-III BOSS catalog to constrain the cosmological parameters governing the expansion history of the universe. The BOSS catalogs are divided into 12 concentric shells over the redshift range 0.25 < z < 0.6, and we repeatedly measure the genus from the two-dimensional galaxy density fields, each time varying the cosmological parameters used to infer the distance–redshift relation to the shells. We also indirectly reconstruct the two-dimensional genus amplitude using the three-dimensional genus measured from SDSS Main Galaxy Sample with galaxies at low redshift z < 0.12. We combine the low- and high-redshift measurements, finding the cosmological model that minimizes the redshift evolution of the genus amplitude, using the fact that this quantity should be conserved. Being a distance measure, the test is sensitive to the matter density parameter (Ω_m) and equation of state of dark energy (w_de). We find a constraint of ${w}_{\mathrm{de}}=-{1.05}_{-0.12}^{+0.13}$, Ω_m = 0.303 ± 0.036 after combining the high- and low-redshift measurements and combining with Planck CMB data. Higher-redshift data and combining data sets at low redshift will allow for stronger constraints.