adsabs/SciX_UAT_keywords huggingface dataset:
On the Relation between the Hard X-Ray Photon Index and Accretion Rate for Super-Eddington Accreting Quasars

We investigate whether the correlation between the hard X-ray photon index ( ${\rm{\Gamma }}$ ) and accretion rate for super-Eddington accreting quasars is different from that for sub-Eddington accreting quasars. We construct a sample of 113 bright quasars from the Sloan Digital Sky Survey Data Release 14 quasar catalog, with 38 quasars as the super-Eddington subsample and 75 quasars as the sub-Eddington subsample. We derive black hole masses using a simple-epoch virial mass formula based on the ${\rm{H}}\beta $ lines, and we use the standard thin disk model to derive the dimensionless accretion rates ( $\dot{{\mathscr{M}}}$ ) for our sample. The X-ray data for these quasars are collected from the Chandra and XMM-Newton archives. We fit the hard X-ray spectra using a single power-law model to obtain ${\rm{\Gamma }}$ values. We find a statistically significant ( ${R}_{{\rm{S}}}=0.43$ , $p=7.75\times {10}^{-3}$ ) correlation between ${\rm{\Gamma }}$ and $\dot{{\mathscr{M}}}$ for the super-Eddington subsample. The ${\rm{\Gamma }}$ - $\dot{{\mathscr{M}}}$ correlation for the sub-Eddington subsample is also significant, but weaker ( ${R}_{{\rm{S}}}=0.30$ , $p=9.98\times {10}^{-3}$ ). Linear regression analysis shows that ${\rm{\Gamma }}=(0.34\pm 0.11)\mathrm{log}\dot{{\mathscr{M}}}+(1.71\pm 0.17)$ and ${\rm{\Gamma }}=(0.09\pm 0.04)\mathrm{log}\dot{{\mathscr{M}}}+(1.93\pm 0.04)$ for the super- and sub-Eddington subsamples, respectively. The ${\rm{\Gamma }}$ - $\dot{{\mathscr{M}}}$ correlations of the two subsamples are different, suggesting different disk-corona connections in these two types of systems. We propose one qualitative explanation of the steeper ${\rm{\Gamma }}$ - $\dot{{\mathscr{M}}}$ correlation in the super-Eddington regime that involves larger seed photon fluxes received by the compact coronae from the thick disks in super-Eddington accreting quasars.

Keywords: accretion; x-ray quasars; supermassive black holes
Is the Radio Source Dipole from NVSS Consistent with the Cosmic Microwave Background and ΛCDM?

The dipole moment in the angular distribution of the cosmic microwave background (CMB) is thought to originate from the doppler effect and our motion relative to the CMB frame. Observations of large-scale structure (LSS) should show a related "kinematic dipole" and help test the kinematic origin of the CMB dipole. Intriguingly, many previous LSS dipole studies suggest discrepancies with the expectations from the CMB. Here, we reassess the apparent inconsistency between the CMB measurements and dipole estimates from the NVSS catalog of radio sources. We find that it is important to account for the shot noise and clustering of the NVSS sources, as well as kinematic contributions, in determining the expected dipole signal. We use the clustering redshift method and a cross-matching technique to refine estimates of the clustering term. We then derive a probability distribution for the expected NVSS dipole in a standard ΛCDM cosmological model including all (i.e., kinematic, shot noise, and clustering) dipole components. Our model agrees with most of the previous NVSS dipole measurements in the literature at better than ≲2σ. We conclude that the NVSS dipole is consistent with a kinematic origin for the CMB dipole within ΛCDM.

Keywords: cosmology; cosmological principle; large-scale structure of the universe; extragalactic radio sources; cosmic microwave background radiation
Digging into the Interior of Hot Cores with ALMA (DIHCA). II. Exploring the Inner Binary (Multiple) System Embedded in G335 MM1 ALMA1

We observed the high-mass protostellar core G335.579-0.272 ALMA1 at ~200 au (0.″05) resolution with the Atacama Large Millimeter/submillimeter Array (ALMA) at 226 GHz (with a mass sensitivity of 5σ = 0.2 M ⊙ at 10 K). We discovered that at least a binary system is forming inside this region, with an additional nearby bow-like structure (≲1000 au) that could add an additional member to the stellar system. These three sources are located at the center of the gravitational potential well of the ALMA1 region and the larger MM1 cluster. The emission from CH3OH (and many other tracers) is extended (>1000 au), revealing a common envelope toward the binary system. We use CH2CHCN line emission to estimate an inclination angle of the rotation axis of 26° with respect to the line of sight based on geometric assumptions and derive a kinematic mass of the primary source (protostar+disk) of 3.0 M ⊙ within a radius of 230 au. Using SiO emission, we find that the primary source drives the large-scale outflow revealed by previous observations. Precession of the binary system likely produces a change in orientation between the outflow at small scales observed here and large scales observed in previous works. The bow structure may have originated from the entrainment of matter into the envelope due to the widening or precession of the outflow, or, alternatively, an accretion streamer dominated by the gravity of the central sources. An additional third source, forming due to instabilities in the streamer, cannot be ruled out as a temperature gradient is needed to produce the observed absorption spectra.

Keywords: star formation; star forming regions; massive stars
Searching in H I for Massive Low Surface Brightness Galaxies: Samples from HyperLeda and the UGC

A search has been made for 21 cm H I line emission in a total of 350 unique galaxies from two samples whose optical properties indicate they may be massive. The first consists of 241 low surface brightness (LSB) galaxies of morphological type Sb and later selected from the HyperLeda database and the second consists of 119 LSB galaxies from the UGC with morphological types Sd-m and later. Of the 350 unique galaxies, 239 were observed at the Nançay Radio Telescope, 161 at the Green Bank Telescope, and 66 at the Arecibo telescope. A total of 295 (84.3%) were detected, of which 253 (72.3%) appear to be uncontaminated by any other galaxies within the telescope beam. Finally, of the total detected, uncontaminated galaxies, at least 31 appear to be massive LSB galaxies, with a total H I mass ≥ 1010 M ⊙, for H 0 = 70 kms-1 Mpc-1. If we expand the definition to also include galaxies with significant total (rather than just gas) mass, i.e., those with an inclination-corrected H I line width W 50,cor > 500 km s-1, this brings the total number of massive LSB galaxies to 41. There are no obvious trends between the various measured global galaxy properties, particularly between mean surface brightness and galaxy mass.

Keywords: amorphous irregular galaxies; radio astronomy; spiral galaxies; low surface brightness galaxies
Nonextensive Behavior of Stellar Rotation in the Galactic Disk Components

The solar neighborhood is a unique stellar astrophysical laboratory formed by a variety of stars from different origins. In particular, two of the most notable populations known are the thick and thin disk stars, each characterized by distinct chemical compositions, ages, kinematics, and origins. Based on Tsallis nonextensive statistics, we investigate the observed distribution of the projected rotational velocity of the thin and thick disk component stars. Through Bayesian inference, our results show that the $v\sin i$ distributions of the Galactic disk populations selected from both kinematic and chemical criteria follow a nonextensive behavior, where non-Gaussian statistics provide a more accurate representation. We also observed an anticorrelation between the entropic index q and the age of disk components confirming the interpretation of initial angular momentum memory loss scaled by the parameter q. In contrast, a subextensivity case with q > 1 was found for the old high-α metal-rich subgroup hαmr, and due to their distinguished rotational behavior and atypical subextensive regime, we infer that thick disk and hαmr stars are, in fact, distinct objects. Our results also suggest that the rotational velocities of stars are defined not only by their evolutionary spin-down processes but also by their birth sites.

Keywords: stellar rotation; stellar kinematics; stellar abundances; galaxy disks; galaxy evolution
Sub-GeV Gamma Rays from Nearby Seyfert Galaxies and Implications for Coronal Neutrino Emission

Recent observations of high-energy neutrinos by IceCube and gamma rays by the Fermi Large Area Telescope (LAT) and the MAGIC telescope have suggested that neutrinos are produced in gamma-ray opaque environments in the vicinity of supermassive black holes. In this work, we present 20 MeV–1 TeV spectra of three Seyfert galaxies whose nuclei are predicted to be active in neutrinos, NGC 4151, NGC 4945, and the Circinus galaxy, using 14.4 yr of Fermi LAT data. In particular, we find evidence of sub-GeV excess emission that can be attributed to gamma rays from NGC 4945, as was also seen in NGC 1068. These spectral features are consistent with predictions of the magnetically powered corona model, and we argue that NGC 4945 is among the brightest neutrino active galaxies detectable for KM3Net and Baikal-GVD. On the other hand, in contrast to other reported results, we do not detect gamma rays from NGC 4151, which constrains neutrino emission from the accretion shock model. Future neutrino detectors such as IceCube-Gen2 and MeV gamma-ray telescopes such as AMEGO-X will be crucial for discriminating among the theoretical models.

Keywords: neutrino astronomy; active galactic nuclei; gamma-ray astronomy; particle astrophysics; supermassive black holes
Effects of Forcing on Shocks and Energy Dissipation in Interstellar and Intracluster Turbulences

Observations indicate that turbulence in the interstellar medium (ISM) is supersonic (M turb ≫ 1) and strongly magnetized (β ~ 0.01-1), while in the intracluster medium (ICM) it is subsonic (M turb ≲ 1) and weakly magnetized (β ~ 100). Here, M turb is the turbulent Mach number and β is the plasma beta. We study the properties of shocks induced in these disparate environments, including the distribution of the shock Mach number, M s , and the dissipation of the turbulent energy at shocks, through numerical simulations using a high-order, accurate code based on the weighted essentially nonoscillatory scheme. In particular, we investigate the effects of different modes of the forcing that drives turbulence: solenoidal, compressive, and a mixture of the two. In ISM turbulence, while the density distribution looks different with different forcings, the velocity power spectrum, P v , on small scales exhibits only weak dependence. Hence, the statistics of shocks depend weakly on forcing either. In the ISM models with M turb ≈ 10 and β ~ 0.1, the fraction of the turbulent energy dissipated at shocks is estimated to be ~15%, not sensitive to the forcing mode. In contrast, in ICM turbulence, P v as well as the density distribution show strong dependence on forcing. The frequency and average Mach number of shocks are greater for compressive forcing than for solenoidal forcing; so is the energy dissipation. The fraction of the ensuing shock dissipation is in the range of ~10%-35% in the ICM models with M turb ≈ 0.5 and β ~ 106. The rest of the turbulent energy should be dissipated through turbulent cascade.

Keywords: interstellar medium; intracluster medium; shocks; magnetic fields; magnetohydrodynamical simulations
Mitigation of LEO Satellite Brightness and Trail Effects on the Rubin Observatory LSST

We report studies on the mitigation of optical effects of bright low-Earth-orbit (LEO) satellites on Vera C. Rubin Observatory and its Legacy Survey of Space and Time (LSST). These include options for pointing the telescope to avoid satellites, laboratory investigations of bright trails on the Rubin Observatory LSST camera sensors, algorithms for correcting image artifacts caused by bright trails, experiments on darkening SpaceX Starlink satellites, and ground-based follow-up observations. The original Starlink v0.9 satellites are g ∼ 4.5 mag, and the initial experiment "DarkSat" is g ∼ 6.1 mag. Future Starlink darkening plans may reach g ∼ 7 mag, a brightness level that enables nonlinear image artifact correction to well below background noise. However, the satellite trails will still exist at a signal-to-noise ratio ∼ 100, generating systematic errors that may impact data analysis and limit some science. For the Rubin Observatory 8.4 m mirror and a satellite at 550 km, the full width at half maximum of the trail is about 3″ as the result of an out-of-focus effect, which helps avoid saturation by decreasing the peak surface brightness of the trail. For 48,000 LEOsats of apparent magnitude 4.5, about 1% of pixels in LSST nautical twilight images would need to be masked.

Keywords: artificial satellites; ccd observation; ccd photometry; observational astronomy; astronomical techniques; photometry; astronomy data analysis; astronomy data acquisition; astronomy data reduction; field of view
The Space Environment and Atmospheric Joule Heating of the Habitable Zone Exoplanet TOI 700 d

We investigate the space environment conditions near the Earth-size planet TOI 700 d using a set of numerical models for the stellar corona and wind, the planetary magnetosphere, and the planetary ionosphere. We drive our simulations using a scaled-down stellar input and a scaled-up solar input in order to obtain two independent solutions. We find that for the particular parameters used in our study, the stellar wind conditions near the planet are not very extreme—slightly stronger than that near the Earth in terms of the stellar wind ram pressure and the intensity of the interplanetary magnetic field. Thus, the space environment near TOI 700 d may not be extremely harmful to the planetary atmosphere, assuming the planet resembles the Earth. Nevertheless, we stress that the stellar input parameters and the actual planetary parameters are unconstrained, and different parameters may result in a much greater effect on the atmosphere of TOI 700 d. Finally, we compare our results to solar wind measurements in the solar system and stress that modest stellar wind conditions may not guarantee atmospheric retention of exoplanets.

Keywords: solar wind; geomagnetic fields; exoplanet atmospheric variability; stellar coronae; stellar winds
Hot Circumsingle Disks Drive Binary Black Hole Mergers in Active Galactic Nucleus Disks

Binary black hole (BBH) mergers, particularly those with component masses in the pair-instability gap, may be produced by hierarchical mergers in the disks surrounding Active Galactic Nuclei (AGNs). While the interaction of an embedded BBH with an AGN disk is typically assumed to facilitate a merger, recent high-resolution hydrodynamical simulations challenge this assumption. However, these simulations often have simplified treatments for gas thermodynamics. In this work, we model the possible consequence of various feedback from an embedded BBH with a simple model that maintains an enhanced temperature profile around each binary component. We show that when the minidisks around each BH become hotter than the background by a factor of three, the BBH orbital evolution switches from expansion to contraction. By analyzing the gravitational torque profile, we find that this change in direction is driven by a weakening of the minidisk spirals and their positive torque on the binary. Our results highlight the important role of thermodynamics around BBHs and its effect on their orbital evolution, suggesting that AGN disks could be efficient factories for BBH mergers.

Keywords: active galactic nuclei; black holes; black hole physics; gravitational wave sources; hydrodynamical simulations; orbital evolution
X-Ray Polarization Variability of High Spectral Peak BL Lacertaes: Cases of 1ES 1959+650 and PKS 2155–304

The high-energy-peaked BL Lacertae objects (HBLs) are the main targets of the Imaging X-ray Polarimetry Explorer (IXPE) for investigating the mechanisms of radiation and particle acceleration in jets. In this Letter, we report the first IXPE observations of two HBLs, 1ES 1959+650 and PKS 2155–304. Both sources exhibit X-ray polarization with a confidence level exceeding 99%, as well as significant variability in polarization across different time intervals and energy ranges. Notably, PKS 2155–304 demonstrates the highest X-ray polarization among all blazars detected by IXPE within its entire energy band (2–8 keV), with a polarization degree of ΠX = 21.9% ± 1.9% (MDP99 ∼ 6.0%). An even higher polarization is observed in the 3–4 keV band, reaching ΠX = 28.6% ± 2.7% (MDP99 ∼ 8.1%) with a confidence level of 10.8σ. Furthermore, no polarization is detected above the 5 keV energy band. For 1ES 1959+650, the highest detected polarization degree in the 2–8 keV band is ΠX = 12.4% ± 0.7% (MDP99 ∼ 2.2%), with an electric vector position angle (EVPA) of ψ X = 19.°7 ± 1.°6. The X-ray polarization of 1ES 1959+650 exhibits evident variability, accompanied by the variations of ψ X, flux, spectrum, and energy bin. We discuss possible implications of these observational findings, including the variability in polarization, rotation of EVPA, and transition between synchrotron and synchrotron–self-Compton. We speculate that the X-rays observed during different IXPE observations originate from distinct regions in the jet and may involve diverse mechanisms for particle acceleration.

Keywords: active galactic nuclei; blazars; polarimetry; x-ray active galactic nuclei
Swift/BAT and RXTE/ASM Observations of the 35 day X-Ray Cycle of Hercules X-1

Swift/BAT and RXTE/ASM observations have monitored the X-ray binary system Her X-1 for approximately 14.5 yr each, and both were monitoring Her X-1 for a period of ∼5.5 yr. Here we study the 35 day cycle using these observations. Using a cross-correlation method we find the times of peaks of the 35 day cycles for ∼150 cycles observed by Swift/BAT and ∼150 cycles observed by RXTE/ASM. These cycles include ∼60 observed with both instruments. The noise level of the RXTE/ASM measurements is larger than that of Swift/BAT, resulting in larger uncertainty in peak times. The distribution of 35 day cycle lengths can be fit with a Gaussian with mean 34.79 days and σ of 1.1 days. The distribution of orbital phases of 35 day cycle peaks is well fit by a uniform distribution, with 76% of the cycles, plus a Gaussian distribution peaked at orbital phase ∼0.5, with 24% of the cycles. We construct the long-term average 35 day lightcurve in the 15-50 keV band from Swift/BAT, and in the 2-12 keV band from RXTE/ASM. The high-energy band shows more variability in the short high state and the low-energy band shows more variability in the main high state. This is consistent with a precessing accretion disk model as the cause of the 35 day cycle.

Keywords: hz herculis x-ray binary stars; x-ray photometry; neutron stars
On Arrival Time Difference Between Lensed Gravitational Waves and Light

It is known that geometrical optics no longer applies to gravitational lensing if the wavelength of a propagating wave becomes comparable to or larger than the Schwarzschild radius of a lensing object. We investigate the propagation of gravitational waves in wave optics, particularly focusing on the difference between their arrival time and the arrival time of light. We argue that, contrary to the observation in the previous work, gravitational waves never arrive at an observer earlier than light when both gravitational waves and light are emitted from a same source simultaneously.

Keywords: gravitational lensing
ALMA Imaging of the CO (7-6) Line Emission in the Submillimeter Galaxy LESS 073 at z = 4.755

In this paper we present our imaging observations on the CO (7-6) line and its underlying continuum emission of the young submillimeter galaxy LESS 073 at redshift 4.755, using the Atacama Large Millimeter/submillimeter Array. At the achieved resolution of ∼ 1.2" × 0.9" (8 × 6 kpc2), the CO (7-6) emission is largely unresolved (with a deconvolved size of 1.1" ± 0.5" × 0.9" ± 0.8), and the continuum emission is totally unresolved. The CO (7-6) line emission has an integrated flux of 0.86 ± 0.08 Jy km s-1, and a line width of 343 ± 40 km s-1. The continuum emission has a flux density of 0.51 mJy. By fitting the observed far-infrared spectral energy distribution (SED) of LESS 073 with a single-temperature modified blackbody function, we obtained a dust temperature Tdust=57.6± 3.5 K, 60-100 μm flux density ratio f60/f100=0.86± 0.08, and total infrared luminosity LIR=(5.8± 0.9)× 1012 L⊙. The SED-fit-based f60/f100 is consistent with those estimated from various line ratios as advocated by our earlier work, indicating that the proposed line-ratio-based method can be used to practically derive f60/f100 for high-z sources. The total molecular gas mass of LESS 073 is (3.3 ± 1.7)× 1010 M⊙, and the inferred gas depletion time is about 43 Myr.

Keywords: high-redshift galaxies; starburst galaxies; interstellar medium; galaxy evolution
On the Possibility of GW190425 Being a Black Hole-Neutron Star Binary Merger

We argue that the kilonova/macronova associated with the gravitational-wave event GW190425 could have been bright enough to be detected if it was caused by the merger of a low-mass black hole (BH) and a neutron star (NS). Although tidal disruption occurs for such a low-mass BH is generally expected, the masses of the dynamical ejecta are limited to ≲10-3 M⊙, which is consistent with previous work in the literature. The remnant disk could be as massive as 0.05-0.1 M⊙, and the disk outflow of ∼0.01-0.03 M⊙ is likely to be driven by viscous or magnetohydrodynamic effects. The disk outflow may not be neutron-rich enough to synthesize an abundance of lanthanide elements, even in the absence of strong neutrino emitter, if the ejection is driven on the viscous timescale of ≳0.3 s. If this is the case, the opacity of the disk outflow is kept moderate, and a kilonova/macronova at the distance of GW190425 reaches a detectable brightness of 20-21 mag at 1 day after merger for most viewing angles. If some disk activity ejects the mass within ∼0.1 s, instead, lanthanide-rich outflows would be launched and the detection of emission becomes challenging. Future possible detections of kilonovae/macronovae from GW190425-like systems will disfavor the prompt collapse of binary NSs and a non-disruptive low-mass BH-NS binary associated with a small NS radius, whose mass ejection is negligible. The host-galaxy distance will constrain the viewing angle and deliver further information about the mass ejection.

Keywords: neutron stars; black holes; gravitational wave sources; compact binary stars; time domain astronomy
Hilbert-Huang Transform Analysis of Quasiperiodic Oscillations in MAXI J1820+070

We present a time-frequency analysis, based on the Hilbert-Huang transform, of the evolution of the low-frequency quasiperiodic oscillations observed in the black hole X-ray binary MAXI J1820+070. Through the empirical mode decomposition method, we decompose the light curve of the quasiperiodic oscillation (QPO) component and measure its intrinsic phase lag between photons from different energy bands. We find that the QPO phase lag is negative (low-energy photons lag behind high-energy photons); meanwhile, the absolute value of the lag increases with energy. By applying the Hilbert transform to the light curve of the QPO, we further extract the instantaneous frequency and amplitude of the QPO. Comparing these results with those from the Fourier analysis, we find that the broadening of the QPO peak is mainly caused by frequency modulation. Through further analysis, we find that these modulations could share a common physical origin with the broadband noise, and can be well explained by the internal shock model of the jet.

Keywords: black hole physics; x-ray binary stars; accretion