Table of contents

The primordial power spectrum describes the initial perturbations in the universe, which eventually grew into the large-scale structure we observe today, and thereby provides an indirect probe of inflation or other structure-formation mechanisms. In this paper, we will investigate the best scales the primordial power spectrum can be probed with in accordance with the knowledge about other cosmological parameters such as Ω_b, Ω_c, Ω_Λ, h, and τ. The aim is to find the most informative way of measuring the primordial power spectrum at different length scales, using different types of surveys and the information they provide for the desired cosmological parameters. We will find the optimal binning of the primordial power spectrum for this purpose by making use of the Fisher matrix formalism. To investigate the correlations between the cosmological parameters, mentioned above, and a set of primordial power spectrum bins, we make use of principal component analysis and the Hermitian square root of the Fisher matrix. The surveys used in this project are Planck and the Sloan Digital Sky Survey (Bright Red Galaxy), but the formalism can easily be extended to any windowed measurements of the perturbation spectrum.

Cosmic rays and magnetic fields can substantially impact the launching of large-scale galactic winds. Many researchers have investigated the role of cosmic rays; our group previously showed that a cosmic-ray and thermally driven wind could explain soft X-ray emission toward the center of the Galaxy. In this paper, we calculate the synchrotron emission from our original wind model and compare it to observations; the synchrotron data show that earlier assumptions about the launching conditions of the wind must be changed: we are required to improve that earlier model by restricting the launching region to the domain of the inner "Molecular Ring," and by decreasing the magnetic field strength from the previously assumed maximum strength. With these physically motivated modifications, we find that a wind model can fit both the radio synchrotron and the X-ray emission, although that model is required to have a higher gas pressure and density than the previous model in order to reproduce the observed X-ray emission within the smaller "footprint." The drop in magnetic field also decreases the effect of cosmic-ray heating, requiring a higher temperature at the base of the wind than the previous model.

We present a detailed study of the hydrodynamics of the matter reinserted by massive stars via stellar winds and supernovae explosions in young assembling galaxies. We show that the interplay between the thermalization of the kinetic energy provided by massive stars, radiative cooling of the thermalized plasma, and the gravitational pull of the host galaxy lead to three different hydrodynamic regimes. These are: (1) the quasi-adiabatic supergalactic winds; (2) the bimodal flows, with mass accumulation in the central zones and gas expulsion from the outer zones of the assembling galaxy; and (3) the gravitationally bound regime, for which all of the gas returned by massive stars remains bound to the host galaxy and is likely to be reprocessed into further generations of stars. Which of the three possible solutions takes place depends on the mass of the star-forming region, its mechanical luminosity (or star formation rate), and its size. The model predicts that massive assembling galaxies with large star formation rates similar to those detected in Submillimeter Common-User Bolometric Array sources (∼1000 M_☉ yr⁻¹) are likely to evolve in a positive star formation feedback condition, either in the bimodal or in the gravitationally bound regime. This implies that star formation in these sources may have little impact on the intergalactic medium and result instead into a fast interstellar matter enrichment, as observed in high redshift quasars.

We use recent Sloan Extension for Galactic Understanding and Exploration (SEGUE) spectroscopy and the Sloan Digital Sky Survey (SDSS) and SEGUE imaging data to measure the sky position, distance, and radial velocities of stars in the tidal debris stream that is commonly referred to as the "Orphan Stream." We fit orbital parameters to the data and find a prograde orbit with an apogalacticon, perigalacticon, and eccentricity of 90 kpc, 16.4 kpc, and e = 0.7, respectively. Neither the dwarf galaxy UMa II nor the Complex A gas cloud has velocities consistent with a kinematic association with the Orphan Stream. It is possible that Segue-1 is associated with the Orphan Stream, but no other known Galactic clusters or dwarf galaxies in the Milky Way lie along its orbit. The detected portion of the stream ranges from 19 to 47 kpc from the Sun and is an indicator of the mass interior to these distances. There is a marked increase in the density of Orphan Stream stars near (l, b) = (253°, 49°), which could indicate the presence of the progenitor at the edge of the SDSS data. If this is the progenitor, then the detected portion of the Orphan Stream is a leading tidal tail. We find blue horizontal branch (BHB) stars and F turnoff stars associated with the Orphan Stream. The turnoff color is (g − r)₀ = 0.22. The BHB stars have a low metallicity of [Fe/H]_WBG = −2.1. The orbit is best fit to a halo potential with a halo plus disk mass of about 2.6 × 10¹¹ M_☉, integrated to 60 kpc from the Galactic center. Our fits are done to orbits rather than full N-body simulations; we show that if N-body simulations are used, the inferred mass of the galaxy would be slightly smaller. Our best fit is found with a logarithmic halo speed of v_halo = 73 ± 24 km s⁻¹, a disk+bulge mass of M(R < 60 kpc) = 1.3 × 10¹¹ M_☉, and a halo mass of M(R < 60 kpc) = 1.4 × 10¹¹ M_☉. However, we can find similar fits to the data that use a Navarro–Frenk–White halo profile or that have smaller disk masses and correspondingly larger halo masses. Distinguishing between different classes of models requires data over a larger range of distances. The Orphan Stream is projected to extend to 90 kpc from the Galactic center, and measurements of these distant parts of the stream would be a powerful probe of the mass of the Milky Way.

Radio loud active galactic nuclei (AGNs) are on average 1000 times brighter in the radio band compared to radio quiet AGNs. We investigate whether this radio loud/quiet dichotomy can be due to differences in the spin of the central black holes (BHs) that power the radio-emitting jets. Using general relativistic magnetohydrodynamic simulations, we construct steady state axisymmetric numerical models for a wide range of BH spins (dimensionless spin parameter 0.1 ⩽ a ⩽ 0.9999) and a variety of jet geometries. We assume that the total magnetic flux through the BH horizon at radius r_H(a) is held constant. If the BH is surrounded by a thin accretion disk, we find that the total BH power output depends approximately quadratically on the angular frequency of the hole, P ∝ Ω²_H ∝ (a/r_H)². We conclude that, in this scenario, differences in the BH spin can produce power variations of only a few tens at most. However, if the disk is thick such that the jet subtends a narrow solid angle around the polar axis, then the power dependence becomes much steeper, P ∝ Ω⁴_H or even ∝Ω⁶_H. Power variations of 1000 are then possible for realistic BH spin distributions. We derive an analytic solution that accurately reproduces the steeper scaling of jet power with Ω_H and we provide a numerical fitting formula that reproduces all our simulation results. We discuss other physical effects that might contribute to the observed radio loud/quiet dichotomy of AGNs.

We present multiwavelength studies of the 106.6 ms γ-ray pulsar PSR J1907+06 near the TeV source MGRO J1908+06. Timing observations with Fermi result in a precise position determination for the pulsar of R.A. = 19^h07^m547(2), decl. = +06°02'16(2)'' placing the pulsar firmly within the TeV source extent, suggesting the TeV source is the pulsar wind nebula of PSR J1907+0602. Pulsed γ-ray emission is clearly visible at energies from 100 MeV to above 10 GeV. The phase-averaged power-law index in the energy range E > 0.1 GeV is Γ = 1.76 ± 0.05 with an exponential cutoff energy E_c = 3.6 ± 0.5 GeV. We present the energy-dependent γ-ray pulsed light curve as well as limits on off-pulse emission associated with the TeV source. We also report the detection of very faint (flux density of ≃ 3.4 μJy) radio pulsations with the Arecibo telescope at 1.5 GHz having a dispersion measure DM = 82.1 ± 1.1 cm⁻³ pc. This indicates a distance of 3.2 ± 0.6 kpc and a pseudo-luminosity of L₁₄₀₀ ≃  0.035 mJy kpc². A Chandra ACIS observation revealed an absorbed, possibly extended, compact (≲4'') X-ray source with significant nonthermal emission at R.A. = 19^h07^m5476, decl. = +06°02'146 with a flux of 2.3^+0.6_−1.4 × 10⁻¹⁴ erg cm⁻² s⁻¹. From archival ASCA observations, we place upper limits on any arcminute scale 2–10 keV X-ray emission of ∼1 × 10⁻¹³ erg cm⁻² s⁻¹. The implied distance to the pulsar is compatible with that of the supernova remnant G40.5 − 0.5, located on the far side of the TeV nebula from PSR J1907+0602, and the S74 molecular cloud on the nearer side which we discuss as potential birth sites.

In the present work, we analyze multiwavelength observations from Hinode, Solar and Heliospheric Observatory (SOHO), and STEREO of the early phases of a coronal mass ejection (CME). We use Hinode/EIS and SOHO/UVCS high-resolution spectra to measure the physical properties of the CME ejecta as a function of time at 1.1 and 1.9 solar radii. Hinode/XRT images are used in combination with EIS spectra to constrain the high temperature plasma properties of the ejecta. SECCHI/EUVI, SECCHI/COR 1, SOHO/EIT, and SOHO/LASCO images are used to measure the CME trajectory, velocity, and acceleration. The combination of measurements of plane of the sky velocities from two different directions allows us to determine the total velocity of the CME plasma up to 5 solar radii. Plasma properties, dynamical status, thermal structure, and brightness distributions are used to constrain the energy content of the CME plasma and to determine the heating rate. We find that the heating is larger than the kinetic energy, and compare it to theoretical predictions from models of CME plasma heating and acceleration.

The effect of a magnetic field on the linear phase of the advective–acoustic instability is investigated as a first step toward a magnetohydrodynamic (MHD) theory of the stationary accretion shock instability taking place during stellar core collapse. We study a toy model where the flow behind a planar stationary accretion shock is adiabatically decelerated by an external potential. Two magnetic field geometries are considered: parallel or perpendicular to the shock. The entropy–vorticity wave, which is simply advected in the unmagnetized limit, separates into five different waves: the entropy perturbations are advected, while the vorticity can propagate along the field lines through two Alfvén waves and two slow magnetosonic waves. The two cycles existing in the unmagnetized limit, advective–acoustic and purely acoustic, are replaced by up to six distinct MHD cycles. The phase differences among the cycles play an important role in determining the total cycle efficiency and hence the growth rate. Oscillations in the growth rate as a function of the magnetic field strength are due to this varying phase shift. A vertical magnetic field hardly affects the cycle efficiency in the regime of super-Alfvénic accretion that is considered. In contrast, we find that a horizontal magnetic field strongly increases the efficiencies of the vorticity cycles that bend the field lines, resulting in a significant increase of the growth rate if the different cycles are in phase. These magnetic effects are significant for large-scale modes if the Alfvén velocity is a sizable fraction of the flow velocity.

We determined the flux ratios of the heavy and eccentric planet XO-3b to its parent star in the four Infrared Array Camera bands of the Spitzer Space Telescope: 0.101% ± 0.004% at 3.6 μm; 0.143% ± 0.006% at 4.5 μm; 0.134% ± 0.049% at 5.8 μm; and 0.150% ± 0.036% at 8.0 μm. The flux ratios are within [−2.2, 0.3, −0.8, and −1.7]σ of the model of XO-3b with a thermally inverted stratosphere in the 3.6 μm, 4.5 μm, 5.8 μm, and 8.0 μm channels, respectively. XO-3b has a high illumination from its parent star (F_p∼ (1.9–4.2) × 10⁹ erg cm⁻² s⁻¹) and is thus expected to have a thermal inversion, which we indeed observe. When combined with existing data for other planets, the correlation between the presence of an atmospheric temperature inversion and the substellar flux is insufficient to explain why some high insolation planets like TrES-3 do not have stratospheric inversions and some low insolation planets like XO-1b do have inversions. Secondary factors such as sulfur chemistry, atmospheric metallicity, amounts of macroscopic mixing in the stratosphere, or even dynamical weather effects likely play a role. Using the secondary eclipse timing centroids, we determined the orbital eccentricity of XO-3b as e = 0.277 ± 0.009. The model radius–age trajectories for XO-3b imply that at least some amount of tidal heating is required to inflate the radius of XO-3b, and the tidal heating parameter of the planet is constrained to Q_p ≲ 10⁶.

We analyze the large-scale two-dimensional sidereal anisotropy of multi-TeV cosmic rays (CRs) by the Tibet Air Shower Array, with the data taken from 1999 November to 2008 December. To explore temporal variations of the anisotropy, the data set is divided into nine intervals, each with a time span of about one year. The sidereal anisotropy of magnitude, about 0.1%, appears fairly stable from year to year over the entire observation period of nine years. This indicates that the anisotropy of TeV Galactic CRs remains insensitive to solar activities since the observation period covers more than half of the 23rd solar cycle.

Both radiative and mechanical feedback from active galactic nuclei have been found to be important for the evolution of elliptical galaxies. We compute how a shock may be driven from a central black hole into the gaseous envelope of an elliptical galaxy by such feedback (in the form of nuclear winds) using high resolution one-dimensional hydrodynamic simulations. We calculate the synchrotron emission from the electron cosmic rays accelerated by the shocks (not the jets) in the central part of elliptical galaxies, and we also study the synchrotron spectrum's evolution using the standard diffusive shock acceleration mechanism, which is routinely applied to supernova remnants. We find quantitative consistency between the synchrotron radio emission produced via this mechanism with extant observations of elliptical galaxies which are undergoing outbursts. Additionally, we also find that synchrotron optical and X-ray emission can co-exist inside elliptical galaxies during a specific evolutionary phase subsequent to central outbursts. In fact, our calculations predict a peak synchrotron luminosity of ∼1.3 × 10⁶ L_☉ at the frequency 5 GHz (radio band), of ∼1.1 × 10⁶ L_☉ at 4.3 × 10¹⁴ Hz (corresponding to the absolute magnitude −10.4 in R band), and of ∼1.5 × 10⁷ L_☉ at 2.4 × 10¹⁷ Hz (soft X-ray, 0.5–2.0 keV band).

Young, massive stars in the Galactic halo are widely supposed to be the result of an ejection event from the Galactic disk forcing some stars to leave their place of birth as so-called runaway stars. Here, we present a detailed spectroscopic and kinematic analysis of the runaway B star HIP 60350 to determine which runaway scenario—a supernova explosion disrupting a binary system or dynamical interaction in star clusters—may be responsible for HIP 60350's peculiar orbit. Based on a non-local thermodynamic equilibrium approach, a high-resolution optical echelle spectrum was examined to revise spectroscopic quantities and for the first time to perform a differential chemical abundance analysis with respect to the B-type star 18 Peg. The results together with proper motions from the Hipparcos Catalog further allowed the three-dimensional kinematics of the star to be studied numerically. The abundances derived for HIP 60350 are consistent with a slightly supersolar metallicity agreeing with the kinematically predicted place of birth ∼6 kpc away from the Galactic center. However, they do not exclude the possibility of an α-enhanced abundance pattern expected in the case of the supernova scenario. Its outstanding high Galactic rest-frame velocity of 530 ± 35 km s⁻¹ is a consequence of ejection in the direction of Galactic rotation and slightly exceeds the local Galactic escape velocity in a standard Galactic potential. Hence, HIP 60350 may be unbound to the Galaxy.

We construct a new sample of 32 obscured active galactic nuclei (AGNs) selected from the Second XMM-Newton Serendipitous Source Catalogue to investigate their multiwavelength properties in relation to the "scattering fraction," the ratio of the soft X-ray flux to the absorption-corrected direct emission. The sample covers a broad range of the scattering fraction (∼0.1%–10%). A quarter of the 32 AGNs have a very low scattering fraction (⩽ 0.5%), which suggests that they are buried in a geometrically thick torus with a very small opening angle. We investigate correlations between the scattering fraction and multiwavelength properties. We find that AGNs with a small scattering fraction tend to have low [O iii]λ5007/X-ray luminosity ratios. This result agrees with the expectation that the extent of the narrow-line region is small because of the small opening angle of the torus. There is no significant correlation between scattering fraction and far-infrared luminosity. This implies that a scale height of the torus is not primarily determined by starburst activity. We also compare scattering fraction with black hole mass or Eddington ratio and find a weak anti-correlation between the Eddington ratio and scattering fraction. This implies that more rapidly growing supermassive black holes tend to have thicker tori.

The high pericenter velocities (up to a few percent of light) of the S stars around the Galactic-center black hole suggest that general relativistic effects may be detectable through the time variation of the redshift during pericenter passage. Previous work has computed post-Newtonian perturbations to the stellar orbits. We study the additional redshift effects due to perturbations of the light path (what one may call "post-Minkowskian" effects), a calculation that can be elegantly formulated as a boundary-value problem. The post-Newtonian and post-Minkowskian redshift effects are comparable: both are $\mathcal O(\beta ^3)$ and amount to a few km s⁻¹ at pericenter for the star S2. On the other hand, the post-Minkowskian redshift contribution of spin is $\mathcal O(\beta ^5)$ and much smaller than the $\mathcal O(\beta ^4)$ post-Newtonian effect, which would be ∼0.1 km s⁻¹ for S2.

Solar prominences are an important tool for studying the structure and evolution of the coronal magnetic field. Here we consider so-called hedgerow prominences, which consist of thin vertical threads. We explore the possibility that such prominences are supported by tangled magnetic fields. A variety of different approaches are used. First, the dynamics of plasma within a tangled field is considered. We find that the contorted shape of the flux tubes significantly reduces the flow velocity compared to the supersonic free fall that would occur in a straight vertical tube. Second, linear force-free models of tangled fields are developed, and the elastic response of such fields to gravitational forces is considered. We demonstrate that the prominence plasma can be supported by the magnetic pressure of a tangled field that pervades not only the observed dense threads but also their local surroundings. Tangled fields with field strengths of about 10 G are able to support prominence threads with observed hydrogen density of the order of 10¹¹ cm⁻³. Finally, we suggest that the observed vertical threads are the result of Rayleigh–Taylor instability. Simulations of the density distribution within a prominence thread indicate that the peak density is much larger than the average density. We conclude that tangled fields provide a viable mechanism for magnetic support of hedgerow prominences.

The solar X-ray continuum emission at five wavelengths between 3.495 Å and 4.220 Å for 19 flares in a 7-month period in 2002–2003 was observed by the RESIK (REntgenovsky Spektrometr s Izognutymi Kristalami) crystal spectrometer on CORONAS-F. In this wavelength region, free–free and free–bound emissions have comparable fluxes. With a pulse-height analyzer having settings close to optimal, the fluorescence background was removed so that RESIK measured true solar continuum in these bands with an uncertainty in the absolute calibration of ±20%. With an isothermal assumption, and temperature and emission measure derived from the ratio of the two GOES channels, the observed continuum emission normalized to an emission measure of 10⁴⁸ cm⁻³ was compared with theoretical continua using the chianti atomic code. The accuracy of the RESIK measurements allows photospheric and coronal abundance sets, important for the free–bound continuum, to be discriminated. It is found that there is agreement to about 25% of the measured continua with those calculated from chianti assuming coronal abundances in which Mg, Si, and Fe abundances are four times photospheric.

It is believed that solar white-light flares (WLFs) originate in the lower chromosphere and upper photosphere. In particular, some recently observed WLFs show a large continuum enhancement at 1.56 μm where the opacity reaches its minimum. Therefore, it is important to clarify how the energy is transferred to the lower layers responsible for the production of WLFs. Based on radiative hydrodynamic simulations, we study the role of non-thermal electron beams in increasing the continuum emission. We vary the parameters of the electron beam and disk positions and compare the results with observations. The electron beam heated model can explain most of the observational white-light enhancements. For the most energetic WLFs observed so far, however, a very large electron beam flux and a high low-energy cutoff, which are possibly beyond the parameter space in our simulations, are required in order to reproduce the observed white-light emission.

We re-investigate the dramatic rise in the S0 fraction, f_S0, within clusters since z ∼ 0.5. In particular, we focus on the role of the global galaxy environment on f_S0 by compiling, either from our own observations or the literature, robust line-of-sight velocity dispersions, σ's, for a sample of galaxy groups and clusters at 0.1 < z < 0.8 that have uniformly determined, published morphological fractions. We find that the trend of f_S0 with redshift is twice as strong for σ < 750 km s⁻¹ groups/poor clusters than for higher-σ, rich clusters. From this result, we infer that over this redshift range galaxy–galaxy interactions, which are more effective in lower-σ environments, are more responsible for transforming spiral galaxies into S0's than galaxy–environment processes, which are more effective in higher-σ environments. The rapid, recent growth of the S0 population in groups and poor clusters implies that large numbers of progenitors exist in low-σ systems at modest redshifts (∼0.5), where morphologies and internal kinematics are within the measurement range of current technology.

Strong gravitational lens systems with measured time delays between the multiple images provide a method for measuring the "time-delay distance" to the lens, and thus the Hubble constant. We present a Bayesian analysis of the strong gravitational lens system B1608+656, incorporating (1) new, deep Hubble Space Telescope (HST) observations, (2) a new velocity-dispersion measurement of 260 ± 15 km s⁻¹ for the primary lens galaxy, and (3) an updated study of the lens' environment. Our analysis of the HST images takes into account the extended source surface brightness, and the dust extinction and optical emission by the interacting lens galaxies. When modeling the stellar dynamics of the primary lens galaxy, the lensing effect, and the environment of the lens, we explicitly include the total mass distribution profile logarithmic slope γ' and the external convergence κ_ext; we marginalize over these parameters, assigning well-motivated priors for them, and so turn the major systematic errors into statistical ones. The HST images provide one such prior, constraining the lens mass density profile logarithmic slope to be γ' = 2.08 ± 0.03; a combination of numerical simulations and photometric observations of the B1608+656 field provides an estimate of the prior for κ_ext: 0.10^+0.08_−0.05. This latter distribution dominates the final uncertainty on H₀. Fixing the cosmological parameters at Ω_m = 0.3, Ω_Λ = 0.7, and w = −1 in order to compare with previous work on this system, we find H₀ = 70.6^+3.1_−3.1 km s⁻¹ Mpc⁻¹. The new data provide an increase in precision of more than a factor of 2, even including the marginalization over κ_ext. Relaxing the prior probability density function for the cosmological parameters to that derived from the Wilkinson Microwave Anisotropy Probe (WMAP) five-year data set, we find that the B1608+656 data set breaks the degeneracy between Ω_m and Ω_Λ at w = −1 and constrains the curvature parameter to be −0.031 < Ω_k < 0.009 (95% CL), a level of precision comparable to that afforded by the current Type Ia SNe sample. Asserting a flat spatial geometry, we find that, in combination with WMAP, H₀ = 69.7^+4.9_−5.0 km s⁻¹ Mpc⁻¹ and w = −0.94^+0.17_−0.19 (68% CL), suggesting that the observations of B1608+656 constrain w as tightly as the current Baryon Acoustic Oscillation data do.

We show for the first time the direct time-variable radio images in the context of shocked accretion flows around a black hole under the general relativistic treatment of both hydrodynamics and radiation transfer. Time variability around a black hole can be induced by the non-axisymmetric standing accretion shock instability (namely, black hole SASI). Since the spiral arm shock waves generate the density and temperature waves at the post-shock region, they cause time variability in the black hole vicinity. Based on our dynamical simulations, we discuss a possibility of detection for the time-variable radio images of M87 by the future space telescope VSOP2/ASTRO-G satellite. The most luminous part of the images is predicted to be near 15 Schwarzschild radii for some snapshots. We show that our results are consistent with existing observational data such as time-averaged radio spectra, Very Long Baseline Array images, and variability timescale for M87. We also discuss observations of M87 with millimeter and submillimeter interferometers.

The timescale for energy release is an important parameter for constraining the coronal heating mechanism. Observations of "warm" coronal loops (∼1 MK) have indicated that the heating is impulsive and that coronal plasma is far from equilibrium. In contrast, observations at higher temperatures (∼3 MK) have generally been consistent with steady heating models. Previous observations, however, have not been able to exclude the possibility that the high temperature loops are actually composed of many small-scale threads that are in various stages of heating and cooling and only appear to be in equilibrium. With new observations from the EUV Imaging Spectrometer and X-ray Telescope (XRT) on Hinode we have the ability to investigate the properties of high temperature coronal plasma in extraordinary detail. We examine the emission in the core of an active region and find three independent lines of evidence for steady heating. We find that the emission observed in XRT is generally steady for hours, with a fluctuation level of approximately 15% in an individual pixel. Short-lived impulsive heating events are observed, but they appear to be unrelated to the steady emission that dominates the active region. Furthermore, we find no evidence for warm emission that is spatially correlated with the hot emission, as would be expected if the high temperature loops are the result of impulsive heating. Finally, we also find that intensities in the "moss," the footpoints of high temperature loops, are consistent with steady heating models provided that we account for the local expansion of the loop from the base of the transition region to the corona. In combination, these results provide strong evidence that the heating in the core of an active region is effectively steady, that is, the time between heating events is short relative to the relevant radiative and conductive cooling times.

A new approximate partition function is derived as a function of temperature and total number density of particles in the given system, and three adjustable parameters. The derivation assumes that we can simulate the calculations of the partition function for hydrogen by means of averages of the energies and sums of the statistical weights. We present the procedure and mathematical process to obtain an approximate analytic function and its derivatives that depend on those parameters. The comparisons with other calculations reported in the literature show good agreement. The free parameters of this function are calculated and given in a table for all the ions of the first 20 atomic species.

We present a detailed strong lensing analysis of a Hubble Space Telescope/Advanced Camera for Surveys legacy data set for the first gravitational lens, Q0957+561. With deep imaging we identify 24 new strongly lensed features, which we use to constrain mass models. We model the stellar component of the lens galaxy using the observed luminosity distribution and the dark matter halo using several different density profiles. We draw on the weak lensing analysis by Nakajima et al. to constrain the mass sheet and environmental terms in the lens potential. Adopting the well-measured time delay, we find H₀ = 85⁺¹⁴₋₁₃ km s⁻¹ Mpc⁻¹ (68% CL) using lensing constraints alone. The principal uncertainties in H₀ are tied to the stellar mass-to-light ratio (a variant of the radial profile degeneracy in lens models). Adding constraints from stellar population synthesis models, we obtain H₀ = 79.3^+6.7_−8.5 km s⁻¹ Mpc⁻¹ (68% CL). We infer that the lens galaxy has a rising rotation curve and a dark matter distribution with an inner core. Intriguingly, we find the quasar flux ratios predicted by our models to be inconsistent with existing radio measurements, suggesting the presence of substructure in the lens.

By using high-resolution one-dimensional hydrodynamical simulations, we investigate the effects of purely mechanical feedback from super massive black holes (SMBHs) in the evolution of elliptical galaxies for a broad range of feedback efficiencies and compare the results to four major observational constraints. In particular, we focus on (1) the central black hole to stellar mass ratio of the host galaxy, (2) the lifetime of the luminous quasar phase, (3) the mass of stars formed in the host galaxy within the last Gyr, and (4) the X-ray luminosity of the hot diffuse gas. As a result, we try to pin down the most successful range of mechanical feedback efficiencies. We find that while low feedback efficiencies result in too much growth of the SMBH, high efficiencies totally blow out the hot interstellar gas, and the models are characterized by very low thermal X-ray luminosity well below the observed range. The net lifetime of the quasar phase is strongly coupled to the mass ratio between SMBH and its host galaxy, while the X-ray luminosity is generally correlated to the recent star formation within the last Gyr. When considering the popularly adopted model of the constant feedback efficiency, the feedback energy deposited into the ambient medium should be more than 0.01% of the SMBH accretion energy to be consistent with the SMBH mass to stellar mass ratio in the local universe. Yet, the X-ray luminosity of the hot gas favors about 0.005% of the accretion energy as the mechanical active galactic nucleus (AGN) feedback energy. We conclude that the purely mechanical feedback mode is unlikely to be simultaneously compatible with all four observable tests, even allowing a broad range of feedback efficiencies, and that including both radiative and mechanical feedback together may be a solution to comply with the observational constraints. In addition to the adopted observational constraints, our simulations also show that the ratio of SMBH growth rate over its current mass and the density and temperature distribution of hot gas can be useful observable diagnostics for AGN feedback efficiencies.

We use data from the Sloan Digital Sky Survey and visual classifications of morphology from the Galaxy Zoo project to study black hole growth in the nearby universe (z < 0.05) and to break down the active galactic nucleus (AGN) host galaxy population by color, stellar mass, and morphology. We find that the black hole growth at luminosities $L[\mbox{O\,{\sc iii}}]$ >10⁴⁰ erg s⁻¹ in early- and late-type galaxies is fundamentally different. AGN host galaxies as a population have a broad range of stellar masses (10¹⁰–10¹¹ M_☉), reside in the green valley of the color–mass diagram and their central black holes have median masses around 10^6.5 M_☉. However, by comparing early- and late-type AGN host galaxies to their non-active counterparts, we find several key differences: in early-type galaxies, it is preferentially the galaxies with the least massive black holes that are growing, while in late-type galaxies, it is preferentially the most massive black holes that are growing. The duty cycle of AGNs in early-type galaxies is strongly peaked in the green valley below the low-mass end (10¹⁰ M_☉) of the red sequence at stellar masses where there is a steady supply of blue cloud progenitors. The duty cycle of AGNs in late-type galaxies on the other hand peaks in massive (10¹¹ M_☉) green and red late-types which generally do not have a corresponding blue cloud population of similar mass. At high-Eddington ratios (L/L_Edd>0.1), the only population with a substantial fraction of AGNs are the low-mass green valley early-type galaxies. Finally, the Milky Way likely resides in the "sweet spot" on the color–mass diagram where the AGN duty cycle of late-type galaxies is highest. We discuss the implications of these results for our understanding of the role of AGNs in the evolution of galaxies.

Despite the extensive study of lithium depletion during pre-main-sequence (PMS) contraction, studies of individual stars show discrepancies between ages determined from the Hertzsprung–Russell (H–R) diagram and ages determined from lithium depletion, indicating open questions in the PMS evolutionary models. To further test these models, we present high-resolution spectra for members of the β Pictoris Moving Group (BPMG), which is young and nearby. We measure equivalent widths of the 6707.8 Å Li i line in these stars and use them to determine lithium abundances. We combine the lithium abundance with the predictions of PMS evolutionary models in order to calculate a lithium depletion age for each star. We compare this age to the age predicted by the H–R diagram of the same model. We find that the evolutionary models underpredict the amount of lithium depletion for the BPMG given its nominal H–R diagram age of ∼12 Myr, particularly for the mid-M stars, which have no observable Li i line. This results in systematically older ages calculated from lithium depletion isochrones than from the H–R diagram. We suggest that this discrepancy may be related to the discrepancy between measured M-dwarf radii and the smaller radii predicted by evolutionary models.

The ability of new instruments for providing accurate inferences of vector magnetic fields and line-of-sight velocities of the solar plasma depends a great deal on the sensitivity to these physical quantities of the spectral lines chosen to be measured. Recently, doubts have been raised about visible Stokes profiles to provide a clear distinction between weak fields and strong ones filling a small fraction of the observed area. The goal of this paper is to give qualitative and quantitative arguments that help in settling the debate since several instruments that employ visible lines are either operating or planned for the near future. The sensitivity of the Stokes profiles is calculated through the response functions (RFs), for e.g., by Ruiz Cobo & Del Toro Iniesta. Both theoretical and empirical evidences are gathered in favor of the reliability of visible Stokes profiles. The RFs are also used for estimating the uncertainties in the physical quantities due to noise in observations. A useful formula has been derived that takes into account the measurement technique (number of polarization measurements, polarimetric efficiencies, and number of wavelength samples), the model assumptions (number of free parameters and the filling factor), and the radiative transfer (RFs). We conclude that a scenario with a weak magnetic field can reasonably be distinguished with visible lines from another with a strong field but a similar Stokes V amplitude, provided that the Milne–Eddington approximation is good enough to describe the solar atmosphere and the polarization signal is at least 3 or 4 times larger than the typical rms noise of 10⁻³I_c reached in the observations.

The power spectrum of density fluctuations in the solar wind is inferred by tracking small timescale changes in the electron plasma frequency during periods of strong Langmuir wave activity. STEREO electric field waveform data are used to produce time profiles of plasma density from which the density power spectrum is derived. The power spectra obtained by this method extend the observed frequency range by an order of magnitude while remaining consistent with previous results near a few Hertz. Density power spectral indices are found to be organized by the angle between the local magnetic field and the solar wind direction, indicating significant anisotropy in solar wind high-frequency density turbulence.

We present a high spatial (diffraction-limited) resolution (∼03) mid-infrared (MIR) spectroscopic study of the nuclei and star-forming regions of four local luminous infrared galaxies (LIRGs) using T-ReCS on the Gemini South telescope. We investigate the spatial variations of the features seen in the N-band spectra of LIRGs on scales of ∼100 pc, which allow us to resolve their nuclear regions and separate the active galactic nucleus (AGN) emission from that of the star formation (SF). We compare (qualitatively and quantitatively) our Gemini T-ReCS nuclear and integrated spectra of LIRGs with those obtained with Spitzer IRS. Star-forming regions and AGNs show distinct features in the MIR spectra, and we spatially separate these, which is not possible using the Spitzer data. The 9.7 μm silicate absorption feature is weaker in the nuclei of the LIRGs than in the surrounding regions. This is probably due to the either clumpy or compact environment of the central AGN or young, nuclear starburst. We find that the [Ne ii]12.81 μm luminosity surface density is tightly and directly correlated with that of Paα for the LIRG star-forming regions (slope of 1.00 ± 0.02). Although the 11.3 μm PAH feature shows also a trend with Paα, this is not common for all the regions and the slope is significantly lower. We also find that the [Ne ii]12.81 μm/Paα ratio does not depend on the Paα equivalent width (EW), i.e., on the age of the ionizing stellar populations, suggesting that, on the scales probed here, the [Ne ii]12.81 μm emission line is a good tracer of the SF activity in LIRGs. On the other hand, the 11.3 μm PAH/Paα ratio increases for smaller values of the Paα EW (increasing ages), indicating that the 11.3 μm PAH feature can also be excited by older stars than those responsible for the Paα emission. Finally, more data are needed in order to address the different physical processes (age of the stellar populations, hardness and intensity of the radiation field, mass of the star-forming regions) affecting the energetics of the polycyclic aromatic hydrocarbon features in a statistical way. Additional high spatial resolution observations are essential to investigating the SF in local LIRGs at the smallest scales and determining ultimately whether they share the same physical properties as high-z LIRGs, ULIRGs, and submillimiter galaxies and therefore belong to the same galaxy population.

We present high-resolution (R ∼ 40,000), high-signal-to-noise ratio (20–90) spectra of an extremely metal-poor giant star Boo−1137 in the "ultra-faint" dwarf spheroidal galaxy (dSph) Boötes I, absolute magnitude M_V ∼ −6.3. We derive an iron abundance of [Fe/H] = –3.7, making this the most metal-poor star as yet identified in an ultra-faint dSph. Our derived effective temperature and gravity are consistent with its identification as a red giant in Boötes I. Abundances for a further 15 elements have also been determined. Comparison of the relative abundances, [X/Fe], with those of the extremely metal-poor red giants of the Galactic halo shows that Boo−1137 is "normal" with respect to C and N, the odd-Z elements Na and Al, the iron-peak elements, and the neutron-capture elements Sr and Ba, in comparison with the bulk of the Milky Way halo population having [Fe/H] ≲−3.0. The α-elements Mg, Si, Ca, and Ti are all higher by Δ[X/Fe] ∼ 0.2 than the average halo values. Monte Carlo analysis indicates that Δ[α/Fe] values this large are expected with a probability ∼0.02. The elemental abundance pattern in Boo–1137 suggests inhomogeneous chemical evolution, consistent with the wide internal spread in iron abundances we previously reported. The similarity of most of the Boo−1137 relative abundances with respect to halo values, and the fact that the α-elements are all offset by a similar small amount from the halo averages, points to the same underlying galaxy-scale stellar initial mass function, but that Boo−1137 likely originated in a star-forming region where the abundances reflect either poor mixing of supernova (SN) ejecta, or poor sampling of the SN progenitor mass range, or both.

We present kinematic and metallicity profiles for the M 31 dwarf elliptical (dE) satellite galaxies NGC 147 and NGC 185. The profiles represent the most extensive spectroscopic radial coverage for any dE galaxy, extending to a projected distance of 8 half-light radii (8r_eff ∼ 14'). We achieve this coverage via Keck/DEIMOS multislit spectroscopic observations of 520 and 442 member red giant branch stars in NGC 147 and NGC 185, respectively. In contrast to previous studies, we find that both dEs have significant internal rotation. We measure a maximum rotational velocity of 17 ±  2 km s⁻¹ for NGC 147 and 15 ±  5 km s⁻¹ for NGC 185. While both rotation profiles suggest a flattening in the outer regions, there is no indication that we have reached the radius of maximum rotation velocity. The velocity dispersions decrease gently with radius with average dispersions of 16 ± 1 km s⁻¹ and 24 ± 1 km s⁻¹ for NGC 147 and NGC 185, respectively. The average metallicities for NGC 147 and NGC 185 are [Fe/H] = −1.1 ± 0.1 and [Fe/H] = −1.3 ± 0.1, respectively; both dEs have internal metallicity dispersions of 0.5 dex, but show no evidence for a radial metallicity gradient. We construct two-integral axisymmetric dynamical models and find that the observed kinematical profiles cannot be explained without modest amounts of non-baryonic dark matter. We measure central mass-to-light ratios of M/L_V = 4.2 ± 0.6 and M/L_V = 4.6 ± 0.6 for NGC 147 and NGC 185, respectively. Both dE galaxies are consistent with being primarily flattened by their rotational motions, although some anisotropic velocity dispersion is needed to fully explain their observed shapes. The velocity profiles of all three Local Group dEs (NGC 147, NGC 185, and NGC 205) suggest that rotation is more prevalent in the dE galaxy class than previously assumed, but often manifests only at several times the effective radius. Since all dEs outside the Local Group have been probed to only inside the effective radius, this opens the door for formation mechanisms in which dEs are transformed or stripped versions of gas-rich rotating progenitor galaxies.

We use the Spitzer Space Telescope to estimate the dayside thermal emission of the exoplanet TrES-3 integrated in the 3.6, 4.5, 5.8, and 8.0 μm bandpasses of the Infrared Array Camera (IRAC) instrument. We observe two secondary eclipses and find relative eclipse depths of 0.00346 ± 0.00035, 0.00372 ± 0.00054, 0.00449 ± 0.00097, and 0.00475 ± 0.00046, respectively, in the four IRAC bandpasses. We combine our results with the earlier K-band measurement of De Mooij et al., and compare them with models of the planetary emission. We find that the planet does not require the presence of an inversion layer in the high atmosphere. This is the first very strongly irradiated planet that does not have a temperature inversion, which indicates that stellar or planetary characteristics other than temperature have an important impact on temperature inversion. De Mooij & Snellen also detected a possible slight offset in the timing of the secondary eclipse in the K band. However, based on our four Spitzer channels, we place a 3σ upper limit of |ecos(ω)| < 0.0056, where e is the planet's orbital eccentricity and ω is the longitude of the periastron. This result strongly indicates that the orbit is circular, as expected from tidal circularization theory.

We present a catalog of Mg ii absorption systems obtained from high-resolution Ultraviolet and Visual Echelle Spectrograph/VLT data of 77 quasi-stellar objects in the redshift range 0.6 < z < 2.0, and down to an equivalent width W₀ ⩾ 0.1 Å. The statistical properties of our sample are found to be in agreement with those from the previous work in the literature. However, we point out that the previously observed increase with redshift of ∂N/∂z for weak absorbers pertains exclusively to very weak absorbers with W₀ < 0.1 Å. Instead, ∂N/∂z for absorbers with W₀ in the range 0.1–0.3 Å actually decreases with redshift, similar to the case of strong absorbers. We then use this catalog to extend our earlier analysis of the links between the Faraday rotation measure (RM) of the quasars and the presence of intervening Mg ii absorbing systems in their spectra. In contrast to the case with strong Mg ii absorption systems (W₀ > 0.3 Å), the weaker systems do not contribute significantly to the observed RM of the background quasars. This is possibly due to the higher impact parameters of the weak systems compared to strong ones, suggesting that the high column density magnetized material that is responsible for the Faraday rotation is located within about 50 kpc of the galaxies. Finally, we show that this result also rules out the possibility that some unexpected secondary correlation between the quasar redshift and its intrinsic RM is responsible for the association of high RM and strong intervening Mg ii absorption that we have presented elsewhere, since this would have produced an equal effect for the weak absorption line systems, which exhibit a very similar distribution of quasar redshifts.

We present infrared JHK photometry of the cataclysmic variable (CV) SDSS J123813.73 − 033933.0 and analyze it along with optical spectroscopy, demonstrating that the binary system is most probably comprised of a massive white dwarf with T_eff = 12000 ± 1000 K and a brown dwarf of spectral type L4. The inferred system parameters suggest that this system may have evolved beyond the orbital period minimum and is a bounce-back system. SDSS J123813.73 − 033933.0 stands out among CVs by exhibiting the cyclical variability that Zharikov et al. called brightenings. These are not related to specific orbital phases of the binary system and are fainter than dwarf novae outbursts that usually occur on longer timescales. This phenomenon has not been observed extensively and, thus, is poorly understood. The new time-resolved, multi-longitude photometric observations of SDSS J123813.73 − 033933.0 allowed us to observe two consecutive brightenings and to determine their recurrence time. The period analysis of all observed brightenings during 2007 suggests a typical timescale that is close to a period of ∼9.3 hr. However, the brightenings modulation is not strictly periodic, possibly maintaining coherence only on timescales of several weeks. The characteristic variability with double orbital frequency that clearly shows up during brightenings is also analyzed. The Doppler mapping of the system shows the permanent presence of a spiral arm pattern in the accretion disk. A simple model is presented to demonstrate that spiral arms in the velocity map appear at the location and phase corresponding to the 2:1 resonance radius and constitute themselves as double-humped light curves. The long-term and short-term variability of this CV is discussed together with the spiral arm structure of an accretion disk in the context of observational effects taking place in bounce-back systems.

We present the Submillimeter Array (SMA) observations of molecular lines at 330 and 340 GHz toward G19.61 − 0.23. The SMA observations have a spatial resolution of ∼2'' and a bandpass of 2 × 2 GHz bandwidth. With the SMA data, we have detected 131 molecular transitions. Ninety-four molecular transitions from 17 species and their isotopomers are identified, including complex organic molecules and simple linear molecules. Most of the complex molecules (CH₃OH, ¹³CH₃OH, C₂H₅OH, HCOOCH₃, HNCO, NH₂CHO, CH₃CN, and CH₃CH₂CN) have a sufficient number of transitions in this observation to allow analysis using the rotational temperature diagram method. The results from rotation temperature diagram fitting have shown that the complex nitrogen-bearing molecules have higher rotation temperatures (296–609 K) and lower column densities (6.5 × 10¹⁵–6.4 × 10¹⁶ cm⁻²). In contrast, the temperatures and column densities of the complex oxygen-bearing molecules range from 95 to 151 K, and from 1.1 × 10¹⁶ to 5.2 × 10¹⁷ cm⁻², respectively. The H₂ column density is estimated from the submillimeter continuum, and the fractional abundances of various species relative to H₂ are calculated. The oxygen-bearing molecules have higher fractional abundances than those of the nitrogen-bearing molecules. The different gas temperatures and fractional abundances suggest a chemical differentiation between oxygen- and nitrogen-bearing molecules. The images of the spatial distribution of different species have shown that the oxygen-bearing and nitrogen-bearing molecules peak at different positions. Through comparing the rotation temperatures and fractional abundances with the spatial distributions of the molecules, we discuss possible chemical processes for producing the complex molecules, as well as nitrogen and oxygen differentiation in G19.61 − 0.23.

Within the framework of the Planck satellite polarization calibration, we present a study of the Crab Nebula spectral energy distribution (SED) over more than six decades in frequency ranging from 1 to 10⁶ GHz (from 299 to 2.99 × 10⁻⁴ mm). The Planck satellite mission observes the sky from 30 to 857 GHz (from 9.99 to 0.3498 mm) and therefore we focus on the millimeter region. We use radio and submillimeter data from the WMAP satellite between 23 and 94 GHz (from 13 to 3.18 mm), from the Archeops balloon experiment between 143 (2.1 mm) and 545 GHz (0.55 mm), and a compendium of other Crab Nebula observations. The Crab SED is compared to models including three main components: synchrotron that is responsible for the emission at low and high frequencies, dust that explains the excess of flux observed by the IRAS satellite, and an extra component on the millimeter regime. From this analysis, we conclude that the unpolarized emission of the Crab Nebula at microwave and millimeter wavelengths is the same synchrotron emission as the one observed in the radio domain. Therefore, we expect the millimeter emission of the Crab Nebula to be polarized with the same degree of polarization and orientation as the radio emission. We set upper limits on the possible errors induced by any millimeter extra component on the reconstruction of the degree and angle of polarization at the percent level as a maximum. This result strongly supports the choice by the Planck collaboration of the Crab Nebula emission for performing polarization cross-checks in the range 30 (299 mm) to 353 GHz (0.849 mm).

When our Sun was young it rotated much more rapidly than now. Observations of young, rapidly rotating stars indicate that many possess substantial magnetic activity and strong axisymmetric magnetic fields. We conduct simulations of dynamo action in rapidly rotating suns with the three-dimensional magnetohydrodynamic anelastic spherical harmonic (ASH) code to explore the complex coupling between rotation, convection, and magnetism. Here, we study dynamo action realized in the bulk of the convection zone for a system rotating at 3 times the current solar rotation rate. We find that substantial organized global-scale magnetic fields are achieved by dynamo action in this system. Striking wreaths of magnetism are built in the midst of the convection zone, coexisting with the turbulent convection. This is a surprise, for it has been widely believed that such magnetic structures should be disrupted by magnetic buoyancy or turbulent pumping. Thus, many solar dynamo theories have suggested that a tachocline of penetration and shear at the base of the convection zone is a crucial ingredient for organized dynamo action, whereas these simulations do not include such tachoclines. We examine how these persistent magnetic wreaths are maintained by dynamo processes and explore whether a classical mean-field α-effect explains the regeneration of poloidal field. We find that the global-scale toroidal magnetic fields are maintained by an Ω-effect arising from the differential rotation, while the global-scale poloidal fields arise from turbulent correlations between the convective flows and magnetic fields. These correlations are not well represented by an α-effect that is based on the kinetic and magnetic helicities.

By assuming a phenomenological form for the ratio of the dark energy and matter densities ρ_X ∝ ρ_ma^ξ, we discuss the cosmic coincidence problem in light of current observational data. Here, ξ is a key parameter to denote the severity of the coincidence problem. In this scenario, ξ = 3 and ξ = 0 correspond to ΛCDM and the self-similar solution without the coincidence problem, respectively. Hence, any solution with a scaling parameter 0 < ξ < 3 makes the coincidence problem less severe. In addition, the standard cosmology without interaction between dark energy and dark matter is characterized by ξ + 3ω_X = 0, where ω_X is the equation of state of the dark energy component, whereas the inequality ξ + 3ω_X ≠ 0 represents non-standard cosmology. We place observational constraints on the parameters (Ω_X,0, ω_X, ξ) of this model, where Ω_X,0 is the present value of density parameter of dark energy Ω_X, by using the Constitution Set (397 supernovae of type Ia data, hereafter SNeIa), the cosmic microwave background shift parameter from the five-year Wilkinson Microwave Anisotropy Probe and the Sloan Digital Sky Survey baryon acoustic peak. Combining the three samples, we get Ω_X,0 = 0.72 ± 0.02, ω_X = −0.98 ± 0.07, and ξ = 3.06 ± 0.35 at 68.3% confidence level. The result shows that the ΛCDM model still remains a good fit to the recent observational data, and the coincidence problem indeed exists and is quite severe, in the framework of this simple phenomenological model. We further constrain the model with the transition redshift (deceleration/acceleration). It shows that if the transition from deceleration to acceleration happens at the redshift z > 0.73, within the framework of this model, we can conclude that the interaction between dark energy and dark matter is necessary.

We investigate the spectral and timing signatures of the internal-shock model for blazars. For this purpose, we develop a semi-analytical model for the time-dependent radiative output from internal shocks arising from colliding relativistic shells in a blazar jet. The emission through synchrotron and synchrotron-self Compton radiation as well as Comptonization of an isotropic external radiation field are taken into account. We evaluate the discrete correlation function (DCF) of the model light curves in order to evaluate features of photon-energy-dependent time lags and the quality of the correlation, represented by the peak value of the DCF. The almost completely analytic nature of our approach allows us to study in detail the influence of various model parameters on the resulting spectral and timing features. This paper focuses on a range of parameters in which the γ-ray production is dominated by Comptonization of external radiation, most likely appropriate for γ-ray bright flat-spectrum radio quasars (FSRQs) or low-frequency peaked BL Lac objects (LBLs). In most cases relevant for FSRQs and LBLs, the variability of the optical emission is highly correlated with the X-ray and high-energy (HE: > 100 MeV) γ-ray emission. Our baseline model predicts a lead of the optical variability with respect to the higher-energy bands by 1–2 hr and of the HE γ-rays before the X-rays by about 1 hr. We show that variations of certain parameters may lead to changing signs of inter-band time lags, potentially explaining the lack of persistent trends of time lags in most blazars.

We examine whether the spectral energy distribution of optical continuum emission of active galactic nuclei (AGNs) changes during flux variation, based on accurate and frequent monitoring observations of 11 nearby Seyfert galaxies and QSOs carried out in the B, V, and I bands for seven years by the MAGNUM telescope. The multi-epoch flux data in any two different bands obtained on the same night show a very tight linear flux-to-flux relationship for all target AGNs. The flux of the host galaxy within the photometric aperture is carefully estimated by surface brightness fitting to available high-resolution Hubble Space Telescope images and MAGNUM images. The flux of narrow emission lines in the photometric bands is also estimated from available spectroscopic data. We find that the non-variable component of the host galaxy plus narrow emission lines for all target AGNs is located on the fainter extension of the linear regression line of multi-epoch flux data in the flux-to-flux diagram. This result strongly indicates that the spectral shape of AGN continuum emission in the optical region (∼4400–7900 Å) does not systematically change during flux variation. The trend of spectral hardening that optical continuum emission becomes bluer as it becomes brighter, which has been reported by many studies, is therefore interpreted as the domination of the variable component of the nearly constant spectral shape of an AGN as it brightens over the non-variable component of the host galaxy plus narrow lines, which is usually redder than AGN continuum emission.

We apply the axisymmetric orbit superposition modeling to estimate the mass of the supermassive black hole (BH) and dark matter (DM) halo profile of NGC 4649. We have included data sets from the Hubble Space Telescope (HST), stellar, and globular cluster (GC) observations. Our modeling gives M_• = (4.5 ± 1.0) × 10⁹ M_☉ and M/L_{V, obs} = 8.7 ± 1.0 (or M/L_V = 8.0 ± 0.9 after foreground Galactic extinction is corrected). We confirm the presence of a DM halo, but the stellar mass dominates inside the effective radius. The parameters of the dark halo are less constrained due to the sparse GC data at large radii. We find that in NGC 4649 the dynamical mass profile from our modeling is consistently larger than that derived from the X-ray data over most of the radial range by roughly 60%–80%. It implies that either some forms of non-thermal pressure need to be included, the assumed hydrostatic equilibrium may not be a good approximation in the X-ray modelings of NGC 4649, or our assumptions used in the dynamical models are biased. Our new M_• is about 2 times larger than the previous published value; the earlier model did not adequately sample the orbits required to match the large tangential anisotropy in the galaxy center. If we assume that there is no DM, the results on the BH mass and M/L_{V, obs} do not change significantly, which we attribute to the inclusion of HST spectra, the sparse GC kinematics, and a diffuse DM halo. Without the HST data, the significance of the BH detection is greatly reduced.

We calculate durations and spectral parameters for 207 Swift bursts detected by the Burst Alert Telescope from 2007 April to 2009 August, including 67 events with measured redshifts. This is the first supplement to our catalog of 425 Swift gamma-ray bursts (GRBs; 147 with redshifts) starting from GRB 041220. This complete and extensive data set, analyzed with a unified methodology, allows us to conduct an accurate census of intrinsic GRB energetics, hardnesses, durations, and redshifts. The GRB world model we derive reproduces well the observables from both Swift and pre-Swift satellites. Comparing to the cosmic star formation rate, we estimate that only about 0.1% of massive stars explode as bright GRBs. There is strong evidence for evolution in the Swift population at intermediate and high-z, and we can rule out (at the 5σ level) that this is due to evolution in the luminosity function of GRBs. Instead, the Swift sample suggests a modest propensity for low metallicity, evidenced by an increase in the rate density with redshift. Treating the multivariate data and selection effects rigorously, we find a real, intrinsic correlation between E_iso and E_pk (and possibly also T_r45,z); however, the correlation is not a narrow log–log relation and its observed appearance is strongly detector-dependent. We also estimate the high-z rate (3%–9% of GRBs at z beyond 5) and discuss the extent of a large missing population of low-E_pk,obs X-ray flashes as well as a potentially large missing population of short-duration GRBs that will be probed by EXIST.

Recently, a new class of radio transients in the 5 GHz band and with durations of the order of hours to days, lacking any visible-light counterparts, was detected by Bower and collaborators. We present new deep near-infrared (IR) observations of the field containing these transients, and find no counterparts down to a limiting magnitude of K = 20.4 mag. We argue that the bright (>1 Jy) radio transients recently reported by Kida et al. are consistent with being additional examples of the Bower et al. transients. We refer to these groups of events as "long-duration radio transients." The main characteristics of this population are: timescales longer than 30 minutes but shorter than several days; very large rate, ∼10³ deg⁻² yr⁻¹; progenitor's sky surface density of >60 deg⁻² (at 95% confidence) at Galactic latitude ∼40°; 1.4–5 GHz spectral slopes, f_ν ∝ ν^α, with α ≳ 0; and most notably the lack of any X-ray, visible-light, near-IR, and radio counterparts in quiescence. We discuss putative known astrophysical objects that may be related to these transients and rule out an association with many types of objects including supernovae, gamma-ray bursts, quasars, pulsars, and M-dwarf flare stars. Galactic brown dwarfs or some sort of exotic explosions in the intergalactic medium remain plausible (though speculative) options. We argue that an attractive progenitor candidate for these radio transients is the class of Galactic isolated old neutron stars (NSs). We confront this hypothesis with Monte Carlo simulations of the space distribution of old NSs, and find satisfactory agreement for the large areal density. Furthermore, the lack of quiescent counterparts is explained quite naturally. In this framework, we find: the mean distance to events in the Bower et al. sample is of order kpc; the typical distance to the Kida et al. transients are constrained to be between 45 pc and 2 kpc (at the 95% confidence level); these events should repeat with a timescale of order several months; and sub-mJy level bursts should exhibit Galactic latitude dependence. We discuss two possible mechanisms giving rise to the observed radio emission: incoherent synchrotron emission and coherent emission. We speculate that if the latter is correct, the long-duration radio transients are sputtering ancient pulsars or magnetars and will exhibit pulsed emission.