Sazuna/UAT_keywords huggingface dataset:
Evidence for Disk Truncation at Low Accretion States of the Black Hole Binary MAXI J1820+070 Observed by NuSTAR and XMM-Newton. We present results from NuSTAR and XMM-Newton observations of the new black hole X-ray binary MAXI J1820+070 at low accretion rates (below 1% of the Eddington luminosity). We detect a narrow Fe Kα emission line, in contrast to the broad and asymmetric Fe Kα line profiles commonly present in black hole binaries at high accretion rates. The narrow line, with weak relativistic broadening, indicates that the Fe Kα line is produced at a large disk radius. Fitting with disk reflection models assuming standard disk emissivity finds a large disk truncation radius (a few tens to a few hundreds of gravitational radii, depending on the disk inclination). In addition, we detect a quasi-periodic oscillation (QPO) varying in frequency between 11.6 ± 0.2 mHz and 2.8 ± 0.1 mHz. The very low QPO frequencies suggest a large size for the optically thin Comptonization region according to the Lense-Thirring precession model, supporting that the accretion disk recedes from the innermost stable circular orbit and is replaced by advection-dominated accretion flow at low accretion rates. We also discuss the possibility of an alternative accretion geometry that the narrow Fe Kα line is produced by a lamppost corona with a large height illuminating the disk.

Keywords: Accretion, Black hole physics, X-ray transient sources, X-ray binary stars
Breaking Resonant Chains: Destabilization of Resonant Planets Due to Long-term Mass Evolution. Recent exoplanet observations reported a large number of multiple-planet systems, in which some of the planets are in a chain of resonances. The fraction of resonant systems to non-resonant systems provides clues about their formation history. We investigated the orbital stability of planets in resonant chains by considering the long-term evolution of planetary mass and stellar mass and using orbital calculations. We found that while resonant chains were stable, they can be destabilized by a change of ∼10% in planetary mass. Such a mass evolution can occur by atmospheric escape due to photoevaporation. We also found that resonant chains can be broken by a stellar mass loss of ≲1%, which would be explained by stellar winds or coronal mass ejections. The long-term mass change of planets and stars plays an important role in the orbital evolutions of planetary systems, including super-Earths.

Keywords: Exoplanet dynamics, Exoplanet evolution, Exoplanet formation
The Rarity of Repeating Fast Radio Bursts from Binary Neutron Star Mergers. Fast radio bursts (FRBs) are extragalactic, bright pulses of emission at radio frequencies with millisecond durations. Observationally, FRBs can be divided into two classes, repeating FRBs and non-repeating FRBs. At present, 20 repeating FRBs have been discovered with unknown physical origins. Localization of the first repeating FRB 121102 and discovery of an associated persistent radio source support that FRBs are powered by young millisecond magnetars, which could be formed by the core-collapses of massive stars or binary neutron star (BNS) mergers. These two formation channels can be distinguished by the gravitational waves generated by BNSs mergers. We first calculate the lower limit of the local formation rate of repeating FRBs observed by the Canadian Hydrogen Intensity Mapping Experiment (CHIME). Then we show that only a small fraction (6%) of repeating FRBs are produced by young magnetars from BNS mergers, based on the gravitational-wave detections by the third observing run (O3) of the Advanced LIGO/Virgo gravitational-wave detectors. Therefore, we believe that repeating FRBs are more likely produced by newborn magnetars newborn from the core-collapses of massive stars rather than magnetars from BNS mergers.

Keywords: Magnetars, Gamma-ray bursts, Gravitational waves, Radio transient sources
The Infrared Medium-deep Survey. VII. Faint Quasars at z ∼ 5 in the ELAIS-N1 Field. The intergalactic medium (IGM) at z ∼ 5 to 6 is largely ionized, and yet the main source for the IGM ionization in the early universe is uncertain. Of the possible contributors are faint quasars with $-26\lesssim {M}_{1450}\lesssim -23$ , but their number density is poorly constrained at z ∼ 5. In this paper, we present our survey of faint quasars at z ∼ 5 in the European Large-Area Infrared Space Observatory Survey-North 1 (ELAIS-N1) field over a survey area of 6.51 deg2 and examine if such quasars can be the dominant source of the IGM ionization. We use the deep optical/near-infrared data of the ELAIS-N1 field as well as the additional medium-band observations to find z ∼ 5 quasars through a two-step approach using the broadband color selection, and spectral energy distribution fitting with the medium-band information included. Adopting Bayesian information criterion, we identify 10 promising quasar candidates. Spectra of three of the candidates are obtained, confirming all of them to be quasars at z ∼ 5 and supporting the reliability of the quasar selection. Using the promising candidates, we derive the z ∼ 5 quasar luminosity function at -26 ≲ M1450 ≲ -23. The number density of faint z ∼ 5 quasars in the ELAIS-N1 field is consistent with several previous results that quasars are not the main contributors to the IGM-ionizing photons at z ∼ 5.

Keywords: Observational astronomy, Early universe, Sky surveys, Quasars, Active galaxies, Active galactic nuclei, Reionization, Near infrared astronomy
The Fourth Fermi-GBM Gamma-Ray Burst Catalog: A Decade of Data. We present the fourth in a series of catalogs of gamma-ray bursts (GRBs) observed with Fermi's Gamma-ray Burst Monitor (Fermi-GBM). It extends the six year catalog by four more years, now covering the 10 year time period from trigger enabling on 2008 July 12 to 2018 July 11. During this time period GBM triggered almost twice a day on transient events, 2356 of which we identified as cosmic GRBs. Additional trigger events were due to solar flare events, magnetar burst activities, and terrestrial gamma-ray flashes. The intention of the GBM GRB catalog series is to provide updated information to the community on the most important observables of the GBM-detected GRBs. For each GRB the location and main characteristics of the prompt emission, the duration, peak flux, and fluence are derived. The latter two quantities are calculated for the 50-300 keV energy band, where the maximum energy release of GRBs in the instrument reference system is observed and also for a broader energy band from 10-1000 keV, exploiting the full energy range of GBM's low-energy detectors. Furthermore, information is given on the settings of the triggering criteria and exceptional operational conditions during years 7 to 10 in the mission. This fourth catalog is an official product of the Fermi-GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center.

Keywords: Gamma-ray bursts, Catalogs
Milky Way Satellite Census. I. The Observational Selection Function for Milky Way Satellites in DES Y3 and Pan-STARRS DR1. We report the results of a systematic search for ultra-faint Milky Way satellite galaxies using data from the Dark Energy Survey (DES) and Pan-STARRS1 (PS1). Together, DES and PS1 provide multi-band photometry in optical/near-infrared wavelengths over ∼80% of the sky. Our search for satellite galaxies targets ∼25,000 deg2 of the high-Galactic-latitude sky reaching a 10σ point-source depth of ≳22.5 mag in the g and r bands. While satellite galaxy searches have been performed independently on DES and PS1 before, this is the first time that a self-consistent search is performed across both data sets. We do not detect any new high-significance satellite galaxy candidates, recovering the majority of satellites previously detected in surveys of comparable depth. We characterize the sensitivity of our search using a large set of simulated satellites injected into the survey data. We use these simulations to derive both analytic and machine-learning models that accurately predict the detectability of Milky Way satellites as a function of their distance, size, luminosity, and location on the sky. To demonstrate the utility of this observational selection function, we calculate the luminosity function of Milky Way satellite galaxies, assuming that the known population of satellite galaxies is representative of the underlying distribution. We provide access to our observational selection function to facilitate comparisons with cosmological models of galaxy formation and evolution.

Keywords: Local Group, Dark matter, Dwarf spheroidal galaxies, Milky Way Galaxy
Milky Way Satellite Census. II. Galaxy-Halo Connection Constraints Including the Impact of the Large Magellanic Cloud. The population of Milky Way (MW) satellites contains the faintest known galaxies and thus provides essential insight into galaxy formation and dark matter microphysics. Here we combine a model of the galaxy-halo connection with newly derived observational selection functions based on searches for satellites in photometric surveys over nearly the entire high Galactic latitude sky. In particular, we use cosmological zoom-in simulations of MW-like halos that include realistic Large Magellanic Cloud (LMC) analogs to fit the position-dependent MW satellite luminosity function. We report decisive evidence for the statistical impact of the LMC on the MW satellite population due to an estimated 6 ± 2 observed LMC-associated satellites, consistent with the number of LMC satellites inferred from Gaia proper-motion measurements, confirming the predictions of cold dark matter models for the existence of satellites within satellite halos. Moreover, we infer that the LMC fell into the MW within the last 2 Gyr at high confidence. Based on our detailed full-sky modeling, we find that the faintest observed satellites inhabit halos with peak virial masses below $3.2\times {10}^{8}\ {M}_{\odot }$ at 95% confidence, and we place the first robust constraints on the fraction of halos that host galaxies in this regime. We predict that the faintest detectable satellites occupy halos with peak virial masses above ${10}^{6}\ {M}_{\odot }$ , highlighting the potential for powerful galaxy formation and dark matter constraints from future dwarf galaxy searches.

Keywords: Milky Way dark matter halo, Galaxy abundances, Dark matter
A Subsolar Metallicity Progenitor for Cassiopeia A, the Remnant of a Type IIb Supernova. We report the detection of the Mn-Kα line in the SN-IIb remnant, Cassiopeia A. Manganese (55Mn after decay of 55Co), a neutron-rich element, together with chromium (52Cr after decay of 52Fe), is mainly synthesized in core-collapse supernovae at the explosive incomplete Si-burning regime. Therefore, the Mn/Cr mass ratio with its neutron excess reflects the neutronization at the relevant burning layer during the explosion. Chandra's deep archival X-ray data of Cassiopeia A indicate a low Mn/Cr mass ratio with values in the range 0.10-0.66, which, when compared to one-dimensional SN explosion models, requires that the electron fraction be 0.4990 ≲ Ye ≲ 0.5 at the incomplete Si-burning layer. An explosion model assuming a solar-metallicity progenitor with a typical explosion energy (1 × 1051 erg) fails to reproduce such a high electron fraction. We can satisfy the observed Mn/Cr mass ratio if the explosive Si-burning regime was to extend into the O/Ne hydrostatic layer, which has a higher Ye. This would require an energetic (&gt;2 × 1051 erg) and/or asymmetric explosion of a subsolar-metallicity progenitor (Z ≲ 0.5Z⊙) for Cassiopeia A. The low initial metallicity can be used to rule out a single-star progenitor, leaving the possibility of a binary progenitor with a compact companion. We discuss the detectability of X-rays from Bondi accretion onto such a compact companion around the explosion site. We also discuss other possible mass-loss scenarios for the progenitor system of Cassiopeia A.

Keywords: X-ray astronomy, Core-collapse supernovae, Nucleosynthesis, Supernova remnants, Stellar evolution
Dusty Cloud Acceleration with Multiband Radiation. We perform two-dimensional and three-dimensional simulations of cold, dense clouds, which are accelerated by radiation pressure on dust relative to a hot, diffuse background gas. We examine the relative effectiveness of acceleration by ultraviolet (UV) and infrared (IR) radiation fields, both independently and acting simultaneously on the same cloud. We study clouds that are optically thin to IR emission but with varying UV optical depths. Consistent with previous work, we find relatively efficient acceleration and long cloud survival times when the IR band flux dominates over the UV flux. However, when the UV flux is dominant or even a modest percentage (∼5%-10%) of the IR irradiating flux, it can act to compress the cloud, first crushing it and then disrupting the outer layers. This drives mixing of the outer regions of the dusty gas with the hot diffuse background to the point where most dust is not likely to survive or stay coupled to the gas. Hence, the cold cloud is unable to survive for a long enough timescale to experience significant acceleration before disruption even though efficient IR cooling keeps the majority of the gas close to the radiative equilibrium temperature (T ≲ 100 K). We discuss the implications for observed systems, concluding that radiation pressure driving is most effective when the light from star-forming regions is efficiently reprocessed into the IR.

Keywords: Galactic winds, Hydrodynamical simulations, Radiative magnetohydrodynamics, Radiative transfer simulations, Interstellar medium wind
Disk Structure around the Class I Protostar L1489 IRS Revealed by ALMA: A Warped-disk System. We have observed the Class I protostar L1489 IRS with the Atacama Millimeter/submillimeter Array (ALMA) in Band 6. The C18O J = 2-1 line emission shows flattened and non-axisymmetric structures in the same direction as its velocity gradient due to rotation. We discovered that the C18O emission shows dips at a radius of ∼200-300 au while the 1.3 mm continuum emission extends smoothly up to r ∼ 400 au. At the radius of the C18O dips, the rotational axis of the outer portion appears to be tilted by ∼15° from that of the inner component. Both the inner and outer components with respect to the C18O dips exhibit the r-0.5 Keplerian rotation profiles until r ∼ 600 au. These results not only indicate that a Keplerian disk extends up to ∼600 au but also that the disk is warped. We constructed a three-dimensional warped-disk model rotating at the Keplerian velocity, and demonstrated that the warped-disk model reproduces main observed features in the velocity channel maps and the PV diagrams. Such a warped-disk system can form by mass accretion from a misaligned envelope. We also discuss a possible disk evolution scenario based on comparisons of disk radii and masses between Class I and Class II sources.

Keywords: Young stellar objects, Star formation, Protoplanetary disks, Circumstellar disks, Protostars
A Deep Exposure in High Resolution X-Rays Reveals the Hottest Plasma in the ζ Puppis Wind. We have obtained a very deep exposure (813 ks) of ζ Puppis (O4 supergiant) with the Chandra HETG Spectrometer. Here we report on analysis of the 1-9 Å region, especially well suited for Chandra, which has a significant contribution from continuum emission between well separated emission lines from high-ionization species. These data allow us to study the hottest plasma present through the continuum shape and emission line strengths. Assuming a power-law emission measure distribution that has a high-temperature cutoff, we find that the emission is consistent with a thermal spectrum having a maximum temperature of 12 MK as determined from the corresponding spectral cutoff. This implies an effective wind shock velocity of 900 km s-1, well below the wind terminal speed of 2250 km s-1. For X-ray emission that forms close to the star, the speed and X-ray flux are larger than can be easily reconciled with strictly self-excited line-deshadowing-instability models, suggesting a need for a fraction of the wind to be accelerated extremely rapidly right from the base. This is not so much a dynamical instability as a nonlinear response to changing boundary conditions.

Keywords: Stellar winds, O stars, X-ray stars
Power-law Pseudo-phase-space Density Profiles of Dark Matter Halos: A Fluke of Physics?. It has been known for nearly 20 yr that the pseudo-phase-space density profile of equilibrium simulated dark matter halos, ρ(r)/σ3(r), is well described by a power law over three decades in radius, even though both the density ρ(r) and the velocity dispersion σ(r) deviate significantly from power laws. The origin of this scale-free behavior is not understood. It could be an inherent property of self-gravitating collisionless systems, or it could be a mere coincidence. To address the question we work with equilibrium halos and, more specifically, the second derivative of the Jeans equation, which, under the assumptions of (I) the Einasto density profile, (II) the linear velocity anisotropy-density slope relation, and (III) ρ/σ3 ∝ r-α, can be transformed from a differential equation to a cubic algebraic equation. Relations (I)-(III) are all observed in numerical simulations and are well parameterized by a total of four or six model parameters. We do not consider the dynamical evolution of halos; instead, taking advantage of the fact that the algebraic Jeans equation for equilibrium halos puts relations (I)-(III) on the same footing, we study the (approximate) solutions of this equation in the four- and six-dimensional spaces. We argue that the distribution of best solutions in these parameter spaces is inconsistent with ρ/σ3 ∝ r-α being a fundamental property of gravitational evolution and conclude that the scale-free nature of this quantity is likely to be a fluke.

Keywords: Cosmology, Dark matter, Dark matter density
Transition from Ordered Pinched to Warped Magnetic Field on a 100 au Scale in the Class 0 Protostar B335. We present our observational results of the 0.87 mm polarized dust emission in the Class 0 protostar B335 obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) at a 0"2 (20 au) resolution. We compared our data at 0.87 mm with those at 1.3 mm from the ALMA archive. The observed polarization orientations at the two wavelengths are consistent within the uncertainty, and the polarization percentages are systematically higher at 1.3 mm than 0.87 mm by a factor of ∼1.7, suggesting that the polarized emission originates from magnetically aligned dust grains. We inferred the magnetic field orientations from the observed polarization orientations. We found that the magnetic field changes from ordered and highly pinched to more complicated and asymmetric structures within the inner 100 au scale of B335, and the magnetic field connects to the center along the equatorial plane as well as along the directions that are ∼40°-60° from the equatorial plane. We performed nonideal MHD simulations of collapsing dense cores. We found that similar magnetic field structures appear in our simulations of dense cores with the magnetic field and rotational axis slightly misaligned by 15° but not in those with the aligned magnetic field and rotational axis. Our results suggest that the midplane of the inner envelope within the inner 100 au scale of B335 could be warped because of the misaligned magnetic field and rotational axis, and the magnetic field could be dragged by the warped accretion flows.

Keywords: Bok globules, Interstellar dynamics, Interstellar magnetic fields, Star formation, Gravitational collapse, Protostars
Response of the High-latitude Upper Mesosphere to Energetic Electron Precipitation. We carried out a statistical study on the effects of strong geomagnetic activity on the mesopause over the auroral region from 2002 to 2018. When the auroral electrojet index increased significantly, the energetic electron precipitation from the Medium Energy Proton and Electron Detector was enhanced by several multiples of 10 for the 55°-70° geomagnetic latitude band. The temperatures measured by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument increased immediately in the mesopause region, together with a descent of the mesopause of about 0.5-2 km. Due to the depth that the precipitation can affect, we conclude that the mesopause is mainly influenced by electrons in the energy range 30-100 keV. The maximum temperature increment at 95 km can reach 4 K and the delay of the response can be up to 1 day. In general, we find that the temperatures significantly respond to the electron precipitation at as low as 93 km, within the mesopause region in most of a year.

Keywords: Mesosphere, Aeronomy, Mesopause, Earth atmosphere
The Evolution of the Inner Regions of Protoplanetary Disks. We present a study of the evolution of the inner few astronomical units of protoplanetary disks around low-mass stars. We consider nearby stellar groups with ages spanning from 1 to 11 Myr, distributed into four age bins. Combining PANSTARSS photometry with spectral types, we derive the reddening consistently for each star, which we use (1) to measure the excess emission above the photosphere with a new indicator of IR excess and (2) to estimate the mass accretion rate ( $\dot{M}$ ) from the equivalent width of the Hα line. Using the observed decay of $\dot{M}$ as a constraint to fix the initial conditions and the viscosity parameter of viscous evolutionary models, we use approximate Bayesian modeling to infer the dust properties that produce the observed decrease of the IR excess with age, in the range between 4.5 and 24 μm. We calculate an extensive grid of irradiated disk models with a two-layered wall to emulate a curved dust inner edge and obtain the vertical structure consistent with the surface density predicted by viscous evolution. We find that the median dust depletion in the disk upper layers is $\epsilon \sim 3\times {10}^{-3}$ at 1.5 Myr, consistent with previous studies, and it decreases to $\epsilon \sim 3\times {10}^{-4}$ by 7.5 Myr. We include photoevaporation in a simple model of the disk evolution and find that a photoevaporative wind mass-loss rate of $\sim 1\mbox{--}3\times {10}^{-9}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ agrees with the decrease of the disk fraction with age reasonably well. The models show the inward evolution of the H2O and CO snowlines.

Keywords: Stellar accretion disks, T Tauri stars, Pre-main sequence stars, Protoplanetary disks