adsabs/SciX_UAT_keywords huggingface dataset:
Kilonova Emission from Black Hole-Neutron Star Mergers. II. Luminosity Function and Implications for Target-of-opportunity Observations of Gravitational-wave Triggers and Blind Searches

We present detailed simulations of the kilonova and gamma-ray burst (GRB) afterglow and kilonova luminosity function from black hole-neutron star (BH-NS) mergers, and discuss the detectability of an electromagnetic (EM) counterpart in connection with gravitational wave (GW) detections, GW-triggered target-of-opportunity observations, and time-domain blind searches. The predicted absolute magnitude of BH-NS kilonovae at 0.5 days after the merger falls in the range [-10, -15.5]. The simulated luminosity function contains potential information on the viewing-angle distribution of the anisotropic kilonova emission. We simulate the GW detection rates, detectable distances, and signal duration for future networks of 2nd/2.5th/3rd generation GW detectors. BH-NSs tend to produce brighter kilonovae and afterglows if the BH has a higher aligned spin, and a less massive NS with a stiffer equation of state. The detectability of kilonovae is especially sensitive to the BH spin. If BHs typically have low spins, the BH-NS EM counterparts are hard to discover. For 2nd generation GW detector networks, a limiting magnitude of mlimit ~ 23-24 mag is required to detect kilonovae even if high BH spin is assumed. Thus, a plausible explanation for the lack of BH-NS-associated kilonova detection during LIGO/Virgo O3 is that either there is no EM counterpart (plunging events) or the current follow-ups are too shallow. These observations still have the chance to detect the on-axis jet afterglow associated with a short GRB or an orphan afterglow. Follow-up observations can detect possible associated short GRB afterglows, from which kilonova signatures may be studied. For time-domain observations, a high-cadence search in redder filters is recommended to detect more BH-NS-associated kilonovae and afterglows.

Keywords: gravitational waves; neutron stars; black holes; gamma-ray bursts
Constructing the Emission-line Galaxy-Host Halo Connection through Auto and Cross Correlations

We investigate the [O II] emission-line galaxy (ELG)-host halo connection via auto and cross correlations, and propose a concise and effective method to populate ELGs in dark matter halos without assuming a parameterized halo occupation distribution (HOD) model. Using the observational data from VIMOS Public Extragalactic Redshift Survey, we measure the auto and cross correlation functions between ELGs selected by [O II] luminosity and normal galaxies selected by stellar mass. Combining the stellar-halo mass relation derived for the normal galaxies and the fraction of ELGs observed in the normal galaxy population, we demonstrate that we can establish an accurate ELG-halo connection. With the ELG-halo connection, we can accurately reproduce the auto and cross correlation functions of ELGs and normal galaxies both in real space and in redshift space, once the satellite fraction is properly reduced. Our method provides a novel strategy to generate ELG mock catalogs for ongoing and upcoming galaxy redshift surveys. We also provide a simple description for the HOD of ELGs.

Keywords: emission line galaxies; redshift surveys; galaxy dark matter halos; dark energy; observational cosmology
NuSTAR Observations of 52 Compton-thick Active Galactic Nuclei Selected by the Swift/Burst Alert Telescope All-sky Hard X-Ray Survey

We present systematic broadband X-ray spectral analysis of 52 Compton-thick ( $24\leqslant \mathrm{log}{N}_{{\rm{H}}}^{\mathrm{LOS}}/{\mathrm{cm}}^{-2}$ ) active galactic nucleus (CTAGN) candidates selected by the Swift/Burst Alert Telescope all-sky hard X-ray survey observed with Chandra, X-ray Multi-Mirror Mission-Newton (XMM-Newton), Swift/X-Ray Telescope, Suzaku, and NuSTAR. The XMM-Newton data of 10 objects and the NuSTAR data of 15 objects are published for the first time. We use an X-ray spectral model from a clumpy torus (XClumpy) to determine the torus properties. As a result, the hydrogen column density along the line of sight ${N}_{{\rm{H}}}^{\mathrm{LOS}}$ obtained from the XClumpy model indicates that 24 objects are Compton-thin AGNs and 28 objects are CTAGNs in a 90% confidence interval. The main reason is the difference in the torus model applied. The hydrogen column density along the equatorial direction ${N}_{{\rm{H}}}^{\mathrm{Equ}}$ of CTAGNs inferred from the XClumpy model is larger than that of less obscured AGNs. The Compton-thin torus covering factor C 22 obtained from the XClumpy model is consistent with that of Ricci et al. in the low Eddington ratio ( $\mathrm{log}{R}_{\mathrm{Edd}}\leqslant -1.0$ ), whereas C 22 inferred from the XClumpy model is larger than that of Ricci et al. in the high Eddington ratio ( $-1.0\leqslant \mathrm{log}{R}_{\mathrm{Edd}}$ ). The average value of the Compton-thick torus covering factor C 24 obtained from the XClumpy model is ${36}_{-4}^{+4}$ %. This value is larger than that of Ricci et al. ( ${C}_{24}\simeq {27}_{-4}^{+4}$ %) based on the assumption that all AGNs have intrinsically the same torus structure. These results suggest that the structure of CTAGNs may be intrinsically different from that of less obscured AGNs.

Keywords: supermassive black holes; x-ray active galactic nuclei; seyfert galaxies; high energy astrophysics; astrophysical black holes; active galactic nuclei
Evolution of LMXBs under Different Magnetic Braking Prescriptions

Magnetic braking (MB) likely plays a vital role in the evolution of low-mass X-ray binaries (LMXBs). However, there is still uncertainty around the physics of MB, and there are various proposed scenarios for MB in the literature. To examine and discriminate the efficiency of MB, we investigate the LMXB evolution with five proposed MB laws. Combining detailed binary evolution calculation with binary population synthesis, we obtain the expected properties of LMXBs and their descendant binary millisecond pulsars. We then discuss the strength and weakness of each MB law by comparing the calculated results with observations. We conclude that the τ-boosted MB law seems to best match the observational characteristics.

Keywords: binary pulsars; neutron stars; x-ray binary stars
Circumnuclear Multi-phase Gas in Circinus Galaxy IV: Absorption Owing to High-J CO Rotational Transitions

We studied the absorption features of CO lines against the continuum originating from the heated dust in the obscuring tori around active galactic nuclei (AGNs). We investigated the formation of absorption lines corresponding to the CO rotational transitions using three-dimensional non-LTE line transfer simulations considering the dust thermal emission. As in Papers I-III of this series, we performed post-processed radiative transfer calculations using the "radiation-driven fountain model" (Wada et al. 2016), which yields a geometrically thick obscuring structure around the nucleus. This model is consistent with the spectral energy distribution of the nearest type-2 Seyfert galaxy, the Circinus galaxy. We found that the continuum-subtracted channel maps of J = 4-3 and higher transitions show absorption regions along the disk midplane for an edge-on viewing angle. The spectra consist of multiple absorption and emission features, reflecting the internal inhomogeneous and turbulent structure of the torus. The deepest absorption feature is caused by the gas on the near side of the torus between r = 10 and 15 pc, which is located in front of the AGN-heated dust inside r ≃ 5 pc. We also found that a spatial resolution of 0.5-1.0 pc is necessary to resolve the absorption features. Moreover, the inclination angle must be close to the edge-on angle (i.e., ≳85°) to observe the absorption features. The findings of the present study imply that combining our radiation-hydrodynamic model with high-resolution observations of CO (7-6) by ALMA can provide new information about the internal structure of the molecular tori in nearby AGNs.

Keywords: active galaxies; active galactic nuclei; radio astrometry
The 26Al Production of the ν e -process in the Explosion of Massive Stars

The core collapses of massive stars at the ends of their lives will produce powerful streams of neutrinos, which provide an important contribution to the 26Al yield during the explosion stage. In this work, the contribution of the process ${}^{26}\mathrm{Mg}{({\nu }_{e},{e}^{-})}^{26}\mathrm{Al}$ to the radioactive 26Al in the Milky Way is studied based on a simple model. By combining the calculation of the neutrino-nucleus cross section and some hypotheses about core-collapse supernova explosions, the ratio of 26Al and 26Mg of the ν e -process is estimated. An analytical relationship between the 26Mg yield and the initial mass and metallicity of massive stars is then obtained, making it easy to estimate the 26Mg and 26Al yields analytically. Due to the simplicity of the model, we can move away from complex calculations and into a careful study of the effects of some important factors, such as the radius of the O/Ne shell, the shock velocity, the neutrino spectrum, the Galactic mass and metallicity distribution, and so on. The uncertainties of the 26Al yield contributed from these factors are discussed in detail. This study will facilitate an intuitive understanding of the buried implicit assumptions in previous studies.

Keywords: core-collapse supernovae; galaxy chemical evolution; gamma-ray astronomy; supernova neutrinos
Ion-neutral Interactions and Nonequilibrium Ionization in the Solar Chromosphere

The thermal structure of the chromosphere is regulated through a complex interaction of various heating processes, radiative cooling, and the ionization degree of the plasma. Here, we study the impact on the thermal properties of the chromosphere when including the combined action of nonequilibrium ionization (NEI) of hydrogen and helium and ion-neutral interaction effects. We have performed a 2.5D radiative magnetohydrodynamic simulation using the Bifrost code. This model includes ion-neutral interaction effects by solving the generalized Ohm' s law (GOL) as well as NEI for hydrogen and helium. The GOL equation includes ambipolar diffusion and the Hall term. We compare this simulation with another simulation that computes the ionization in local thermodynamic equilibrium (LTE) including ion-neutral interaction effects. Our numerical models reveal substantial thermal differences in magneto-acoustic shocks, the wake behind the shocks, spicules, low-lying magnetic loops, and the transition region. In particular, we find that heating through ambipolar diffusion in shock wakes is substantially less efficient, while in the shock fronts themselves it is more efficient, under NEI conditions than when assuming LTE.

Keywords: solar chromosphere; solar chromospheric heating; magnetohydrodynamical simulations; solar magnetic fields; solar spicules; radiative magnetohydrodynamics
Does Turbulence along the Coronal Current Sheet Drive Ion Cyclotron Waves?

Evidence for the presence of ion cyclotron waves (ICWs), driven by turbulence, at the boundaries of the current sheet is reported in this paper. By exploiting the full potential of the joint observations performed by Parker Solar Probe and the Metis coronagraph on board Solar Orbiter, local measurements of the solar wind can be linked with the large-scale structures of the solar corona. The results suggest that the dynamics of the current sheet layers generates turbulence, which in turn creates a sufficiently strong temperature anisotropy to make the solar-wind plasma unstable to anisotropy-driven instabilities such as the Alfvén ion cyclotron, mirror-mode, and firehose instabilities. The study of the polarization state of high-frequency magnetic fluctuations reveals that ICWs are indeed present along the current sheet, thus linking the magnetic topology of the remotely imaged coronal source regions with the wave bursts observed in situ. The present results may allow improvement of state-of-the-art models based on the ion cyclotron mechanism, providing new insights into the processes involved in coronal heating.

Keywords: magnetohydrodynamics; interplanetary turbulence; alfven waves; solar corona; solar coronal heating; coronagraphic imaging; solar wind; heliosphere; space plasmas
Calibration of the MaGIXS Experiment. I. Calibration of the X-Ray Source at the X-Ray and Cryogenic Facility

The Marshall Grazing Incidence Spectrometer (MaGIXS) is a sounding rocket experiment that will observe the soft X-ray spectrum of the Sun from 24 to 6.0 Å (0.5-2.0 keV) and is scheduled for launch in 2021. Component- and instrument-level calibrations for the MaGIXS instrument are carried out using the X-ray and Cryogenic Facility (XRCF) at NASA Marshall Space Flight Center. In this paper, we present the calibration of the incident X-ray flux from the electron impact source with different targets at the XRCF using a CCD camera; the photon flux at the CCD was low enough to enable its use as a "photon counter," i.e., the ability to identify individual photon hits and calculate their energy. The goal of this paper is two-fold: (1) to confirm that the flux measured by the XRCF beam normalization detectors is consistent with the values reported in the literature and therefore reliable for MaGIXS calibration and (2) to develop a method of counting photons in CCD images that best captures their number and energy.

Keywords: solar corona; solar x-ray emission; flux calibration; x-ray telescopes; x-ray detectors
AGILESim: Monte Carlo Simulation of the AGILE Gamma-Ray Telescope

The accuracy of Monte Carlo simulations in reproducing the scientific performance of space telescopes (e.g., angular resolution) is mandatory for a correct design of the mission. A brand-new Monte Carlo simulator of the Astrorivelatore Gamma ad Immagini LEggero (AGILE)/Gamma-Ray Imaging Detector (GRID) space telescope, AGILESim, is built using the customizable Bologna Geant4 Multi-Mission Simulator (BoGEMMS) architecture and the latest Geant4 library to reproduce the instrument performance of the AGILE/GRID instrument. The Monte Carlo simulation output is digitized in the BoGEMMS postprocessing pipeline, according to the instrument electronic readout logic, then converted into the onboard data handling format, and finally analyzed by the standard mission on-ground reconstruction pipeline, including the Kalman filter, as a real observation in space. In this paper we focus on the scientific validation of AGILESim, performed by reproducing (I) the conversion efficiency of the tracker planes, (II) the tracker charge readout distribution measured by the on-ground assembly, integration, and verification activity, and (III) the point-spread function of in-flight observations of the Vela pulsar in the 100 MeV-1 GeV energy range. We measure an in-flight angular resolution (full width at half-maximum) for Vela-like point sources of $2\buildrel{\circ}\over{.} {0}_{-0\buildrel{\circ}\over{.} 3}^{+0\buildrel{\circ}\over{.} 2}$ and $0\buildrel{\circ}\over{.} {8}_{-0\buildrel{\circ}\over{.} 1}^{+0\buildrel{\circ}\over{.} 1}$ in the 100-300 and 300-1000 MeV energy bands, respectively. The successful cross-comparison of the simulation results with the AGILE on-ground and in-space performance validates the BoGEMMS framework for its application to future gamma-ray trackers (e.g., e-ASTROGAM and AMEGO).

Keywords: astronomical instrumentation; gamma-ray telescopes; astronomical simulations
Fast Gravitational-wave Parameter Estimation without Compromises

We present a lightweight, flexible, and high-performance framework for inferring the properties of gravitational-wave events. By combining likelihood heterodyning, automatically differentiable, and accelerator-compatible waveforms, and gradient-based Markov Chain Monte Carlo sampling enhanced by normalizing flows, we achieve full Bayesian parameter estimation for real events like GW150914 and GW170817 within a minute of sampling time. Our framework does not require pretraining or explicit reparameterizations and can be generalized to handle higher dimensional problems. We present the details of our implementation and discuss trade-offs and future developments in the context of other proposed strategies for real-time parameter estimation. Our code for running the analysis is publicly available on GitHub at https://github.com/kazewong/jim.

Keywords: gravitational waves; markov chain monte carlo; astronomical methods; computational methods; algorithms; neural networks; gpu computing
On Single-pulse Energies of Some Bright Pulsars Observed at 1.7 GHz

We present Arecibo observations of the bright pulsars B0301+19, B0525+21, B0540+23, B0611+22, and B0823+26 at 1.7 GHz with 100 MHz bandwidth. No giant pulses were found, except for B0823+26, where we recorded a giant interpulse with 230 times the average peak intensity. The postcursor in B0823+26 shows a symmetric double-peaked structure, indicating that it is frequency dependent. In all pulsars, for a given single-pulse peak intensity there is a range of equivalent widths up to a maximum, which becomes smaller the stronger the pulses are, thereby apparently limiting the energy output. Forming average profiles from pulses with certain equivalent widths leads to profiles with changing component characteristics and could allow exploring the magnetosphere at different heights, assuming a dipolar field geometry. We found that the normalized lag-1 autocorrelation coefficient for single-pulse energies can be over 0.5, indicating high correlations. From the first peak of the energy autocorrelation function a so-far-unobserved 15-period modulation is found for B0540+23, as well as a possible 10-period modulation for B0611+22. We also show that a fit of the Weibull distribution to the cumulative probability for the energies yields a better fit than the usual lognormal distribution. The cumulative probability distributions permit an estimate of the nulling fraction, which ranges from 0.6% for B0611+22 to 24% for B0525+21.

Keywords: radio pulsars
Fast Multipole Methods for N-body Simulations of Collisional Star Systems

Direct N-body simulations of star clusters are accurate but expensive, largely due to the numerous ${ \mathcal O }({N}^{2})$ pairwise force calculations. To solve the post-million-body problem, it will be necessary to use approximate force solvers, such as tree codes. In this work, we adapt a tree-based, optimized Fast Multipole Method (FMM) to the collisional N-body problem. The use of a rotation-accelerated translation operator and an error-controlled cell opening criterion leads to a code that can be tuned to arbitrary accuracy. We demonstrate that our code, Taichi, can be as accurate as direct summation when N > 104. This opens up the possibility of performing large-N, star-by-star simulations of massive stellar clusters and would permit large parameter space studies that would require years with the current generation of direct summation codes. Using a series of tests and idealized models, we show that Taichi can accurately model collisional effects, such as dynamical friction and the core-collapse time of idealized clusters, producing results in strong agreement with benchmarks from other collisional codes such as NBODY6++GPU or PeTar. Parallelized using OpenMP and AVX, Taichi is demonstrated to be more efficient than other CPU-based direct N-body codes for simulating large systems. With future improvements to the handling of close encounters and binary evolution, we clearly demonstrate the potential of an optimized FMM for the modeling of collisional stellar systems, opening the door to accurate simulations of massive globular clusters, super star clusters, and even galactic nuclei.

Keywords: star clusters; stellar dynamics
The Hubble Space Telescope Survey of M31 Satellite Galaxies. II. The Star Formation Histories of Ultrafaint Dwarf Galaxies

We present the lifetime star formation histories (SFHs) for six ultrafaint dwarf (UFD; M V > - 7.0, $4.9\lt {\mathrm{log}}_{10}({M}_{* }(z=0)/{M}_{\odot })\lt 5.5$ ) satellite galaxies of M31 based on deep color-magnitude diagrams constructed from Hubble Space Telescope imaging. These are the first SFHs obtained from the oldest main-sequence turnoff of UFDs outside the halo of the Milky Way (MW). We find that five UFDs formed at least 50% of their stellar mass by z = 5 (12.6 Gyr ago), similar to known UFDs around the MW, but that 10%-40% of their stellar mass formed at later times. We uncover one remarkable UFD, And XIII, which formed only 10% of its stellar mass by z = 5, and 75% in a rapid burst at z ~ 2-3, a result that is robust to choices of underlying stellar model and is consistent with its predominantly red horizontal branch. This "young" UFD is the first of its kind and indicates that not all UFDs are necessarily quenched by reionization, which is consistent with predictions from several cosmological simulations of faint dwarf galaxies. SFHs of the combined MW and M31 samples suggest reionization did not homogeneously quench UFDs. We find that the least-massive MW UFDs (M *(z = 5) ≲ 5 × 104 M ⊙) are likely quenched by reionization, whereas more-massive M31 UFDs (M *(z = 5) ≳ 105 M ⊙) may only have their star formation suppressed by reionization and quench at a later time. We discuss these findings in the context of the evolution and quenching of UFDs.

Keywords: andromeda galaxy; dwarf galaxies; hertzsprung russell diagram; reionization; galaxy quenching
Don't Believe the Hype(r): The Yellow Supergiants of Westerlund 1

Yellow hypergiants (YHGs) are often presumed to represent a transitional post-red supergiant (RSG) phase for stars ~30-40 M ⊙. Here we present visual-wavelength echelle spectra of six YHG candidates in the Galactic cluster Westerlund 1, and we compare them to known YHGs, IRC +10420 and Hen 3-1979. We find that the six YHG candidates do not exhibit any metal emission lines, nor do they show strong Hα emission, and as such do not meet the criteria necessary to be classified as YHGs. In conjunction with their moderate luminosities of $\mathrm{log}(L/{L}_{\odot })$ = 4.7-5.4 estimated from optical/infrared photometry, we suggest instead that they are normal yellow supergiants (YSGs) with more modest initial masses around 15-20 M ⊙. This adds additional support to the hypothesis that Wd1 is a multiage cluster with an older age than previously assumed, and is not a ~5 Myr old cluster caught at a very specific transitional point when single-star evolution might yield Wolf-Rayet stars, luminous blue variables, RSGs, and YHGs in the same cluster. Nevertheless, the population of YSGs in Wd1 is very unusual, with YSGs outnumbering RSGs, but with both spanning a large luminosity range. Here, we discuss evolutionary scenarios that might have led to the high fraction of YSGs. The number of YSGs and their significant luminosity spread cannot be explained by simple population synthesis models with single or binary stars. Even with multiple ages or a large age spread, the high YSG/RSG ratio remains problematic. We suggest instead that the objects may experience a prolonged YSG phase due to evolution in triple systems.

Keywords: massive stars; stellar evolution; supergiant stars