Sazuna/UAT_keywords huggingface dataset:
The Faint End of the Quasar Luminosity Function at z ∼ 5 from the Subaru Hyper Suprime-Cam Survey. We present the quasar luminosity function at z ∼ 5 derived from the optical wide-field survey data obtained as a part of the Subaru strategic program (SSP) with the Hyper Suprime-Cam (HSC). From a ∼81.8 deg2 area in the Wide layer of the HSC-SSP survey, we selected 224 candidates of low-luminosity quasars at z ∼ 5 by adopting the Lyman-break method down to i = 24.1 mag. Based on our candidates and spectroscopically confirmed quasars from the Sloan Digital Sky Survey (SDSS), we derived the quasar luminosity function at z ∼ 5, covering a wide luminosity range of -28.76 &lt; M1450 &lt; -22.32 mag. We found that the quasar luminosity function is fitted by a double power-law model with a break magnitude of ${M}_{1450}^{* }=-{25.05}_{-0.24}^{+0.10}$ mag. The inferred number density of low-luminosity quasars is lower, and the derived faint-end slope, $-{1.22}_{-0.10}^{+0.03}$ , is flatter than those of previous studies at z ∼ 5. A compilation of the quasar luminosity function at 4 ≤ z ≤ 6 from the HSC-SSP suggests that there is little redshift evolution in the break magnitude and in the faint-end slope within this redshift range, although previous studies suggest that the faint-end slope becomes steeper at higher redshifts. The number density of low-luminosity quasars decreases more rapidly from z ∼ 5 to z ∼ 6 than from z ∼ 4 to z ∼ 5.

Keywords: Luminosity function, Supermassive black holes, Active galaxies, Quasars
Stratified Global MHD Models of Accretion Disks in Semidetached Binaries. We present results of the first global magnetohydrodynamic simulations of accretion disks fed by Roche-lobe overflow, including vertical stratification, in order to investigate the roles of spiral shocks, magnetorotational instability (MRI), and the accretion stream in disk structure and evolution. Our models include a simple treatment of gas thermodynamics, with orbital Mach numbers at the inner edge of the disk Min of 5 and 10. We find mass accretion rates to vary considerably on all timescales, with only the Mach 5 model reaching a clear quasi-stationary state. For Mach 10, the model undergoes an outside-in, magnetically driven accretion event occurring on a timescale of ∼10 orbital periods of the binary. Both models exhibit spiral shocks inclined with respect to the binary plane, with their position and inclination changing rapidly. However, the time-averaged location of these shocks in the equatorial plane is well fit by simple linear models. MRI turbulence in the disk generates toroidal magnetic field patterns (butterfly diagrams) that are in some cases irregular, perhaps due to interaction with the spiral structure. While many of our results are in good agreement with local studies, we find some features (most notably those related to spiral shocks) can only be captured in global models such as studied here. Thus, while global studies remain computationally expensive—even as idealized models—they are essential (along with more sophisticated treatment of radiation transport and disk thermodynamics) for furthering our understanding of accretion in binary systems.

Keywords: Stellar accretion disks, Cataclysmic variable stars, Semi-detached binary stars, Magnetohydrodynamical simulations
X-Ray through Very High Energy Intrabinary Shock Emission from Black Widows and Redbacks. Black widow and redback systems are compact binaries in which a millisecond pulsar heats and may even ablate its low-mass companion by its intense wind of relativistic particles and radiation. In such systems, an intrabinary shock can form as a site of particle acceleration and associated nonthermal emission. We model the X-ray and gamma-ray synchrotron and inverse Compton spectral components for select spider binaries, including diffusion, convection, and radiative energy losses in an axially symmetric, steady-state approach. Our new multizone code simultaneously yields energy-dependent light curves and orbital-phase-resolved spectra. Using parameter studies and matching the observed X-ray spectra and light curves, as well as Fermi Large Area Telescope spectra where available, with a synchrotron component, we can constrain certain model parameters. For PSR J1723-2837 these are notably the magnetic field and bulk flow speed of plasma moving along the shock tangent, the shock acceleration efficiency, and the multiplicity and spectrum of pairs accelerated by the pulsar. This affords a more robust prediction of the expected high-energy and very high energy gamma-ray flux. We find that nearby pulsars with hot or flaring companions may be promising targets for the future Cerenkov Telescope Array. Moreover, many spiders are likely to be of significant interest to future MeV-band missions such as AMEGO and e-ASTROGAM.

Keywords: Millisecond pulsars, Close binary stars, Stellar winds, Non-thermal radiation sources, Gamma-ray astronomy
First Discovery of a Fast Radio Burst at 350 MHz by the GBNCC Survey. We report the first discovery of a fast radio burst (FRB), FRB 20200125A, by the Green Bank Northern Celestial Cap (GBNCC) Pulsar Survey conducted with the Green Bank Telescope at 350 MHz. FRB 20200125A was detected at a Galactic latitude of 58°43 with a dispersion measure of 179 pc cm3, while electron density models predict a maximum Galactic contribution of 25 pc cm3 along this line of sight. Moreover, no apparent Galactic foreground sources of ionized gas that could account for the excess DM are visible in multiwavelength surveys of this region. This argues that the source is extragalactic. The maximum redshift for the host galaxy is zmax = 0.17, corresponding to a maximum comoving distance of approximately 750 Mpc. The measured peak flux density for FRB 20200125A is 0.37 Jy, and we measure a pulse width of 3.7 ms, consistent with the distribution of FRB widths observed at higher frequencies. Based on this detection and assuming a Euclidean flux density distribution of FRBs, we calculate an all-sky rate at 350 MHz of ${3.4}_{-3.3}^{+15.4}\times {10}^{3}$ FRBs sky-1 day-1 above a peak flux density of 0.42 Jy for an unscattered pulse having an intrinsic width of 5 ms, consistent with rates reported at higher frequencies, albeit with large uncertainties. Given the recent improvements in our single-pulse search pipeline, we also revisit the GBNCC survey sensitivity to various burst properties. Finally, we find no evidence of strong interstellar scattering in FRB 20200125A, adding to the growing evidence that some FRBs have circumburst environments where free-free absorption and scattering are not significant.

Keywords: Surveys, Radio bursts, Radio transient sources
Breaking the Dark Degeneracy with the Drifting Coefficient of the Field Cluster Mass Function. We present a numerical analysis supporting the evidence that the redshift evolution of the drifting coefficient of the field cluster mass function is capable of breaking several cosmic degeneracies. This evidence is based on the data from the CoDECS and DUSTGRAIN-pathfinder simulations performed separately for various nonstandard cosmologies including coupled dark energy, f(R) gravity, and combinations of f(R) gravity with massive neutrinos as well as for the standard Λ cold dark matter (ΛCDM) cosmology. We first numerically determine the field cluster mass functions at various redshifts in the range of 0 ≤ z ≤ 1 for each cosmology. Then, we compare the analytic formula developed in previous works with the numerically obtained field cluster mass functions by adjusting its drifting coefficient, β, at each redshift. It is found that the analytic formula with the best-fit coefficient provides a good match to the numerical results at all redshifts for all of the cosmologies. The empirically determined redshift evolution of the drifting coefficient, β(z), turns out to significantly differ among different cosmologies. It is also shown that even without using any prior information on the background cosmology the drifting coefficient, β(z), can discriminate with high statistical significance the degenerate nonstandard cosmologies not only from the ΛCDM but also from one another. It is concluded that the evolution of the departure from the Einstein-de Sitter state and spherically symmetric collapse processes quantified by β(z) is a powerful probe of gravity and dark sector physics.

Keywords: Cosmological models, Large-scale structure of the universe
Radio and X-Ray Observations of Short-lived Episodes of Electron Acceleration in a Solar Microflare. Solar flares are sudden energy release events in the solar corona, resulting from magnetic reconnection, that accelerate particles and heat the ambient plasma. During a flare, there are often multiple temporally and spatially separated individual energy release episodes that can be difficult to resolve depending on the observing instrument. We present multiwavelength imaging and spectroscopy observations of multiple electron acceleration episodes during a GOES B1.7-class two-ribbon flare on 2012 February 25, observed simultaneously with the Karl G. Jansky Very Large Array at 1-2 GHz, the Reuven Ramatay High Energy Solar Spectroscopic Imager in X-rays, and the Solar Dynamics Observatory in extreme ultraviolet. During the initial phase of the flare, five radio bursts were observed. A nonthermal X-ray source was seen to be cotemporal but not cospatial with the first three radio bursts. Their radio spectra are interpreted as optically thick gyrosynchrotron emission. By fitting the radio spectra with a gyrosynchrotron model, we derive the magnetic field strength and nonthermal electron spectral parameters in each acceleration episode. Notably, the nonthermal parameters derived from X-rays differ considerably from the nonthermal parameters inferred from the radio. The observations are indicative of multiple cotemporal acceleration episodes during the impulsive phase of a solar microflare. The X-ray and radio burst sources likely originate from separate electron distributions in different magnetic loops.

Keywords: Solar flares, Solar energetic particles, The Sun, Solar radio emission, Solar radio flares
Spectroscopic Observations of High-speed Downflows in a C1.7 Solar Flare. In this paper, we analyze the high-resolution UV spectra for a C1.7 solar flare (SOL2017-09-09T06:51) observed by the Interface Region Imaging Spectrograph (IRIS). We focus on the spectroscopic observations at the locations where the cool lines of Si IV 1402.8 Å (∼104.8 K) and C II 1334.5/1335.7 Å (∼104.4 K) reveal significant redshifts with Doppler velocities up to ∼150 km s-1. These redshifts appear in the rise phase of the flare, then increase rapidly, reach the maximum in a few minutes, and proceed into the decay phase. Combining the images from IRIS and Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we propose that the redshifts in the cool lines are caused by the downflows in the transition region and upper chromospheric layers, which likely result from a magnetic reconnection leading to the flare. In addition, the cool Si IV and C II lines show gentle redshifts (a few tens of km s-1) at some other locations, which manifest some distinct features from the above locations. This is supposed to originate from a different physical process.

Keywords: Ultraviolet astronomy, Solar flares, Active solar chromosphere, Solar magnetic reconnection
The Statistical Relationship between White-light Emission and Photospheric Magnetic Field Changes in Flares. Continuum emission, also called white-light emission (WLE), and permanent changes of the magnetic field (ΔBLOS) are often observed during solar flares. However, their relation and precise mechanisms are still unknown. We study statistically the relationship between ΔBLOS and WLE during 75 solar flares of different strengths and locations on the solar disk. We analyze SDO/HMI data and determine for each pixel in each flare if it exhibited WLE and/or ΔBLOS. We then investigate the occurrence, strength, and spatial size of the WLE, its dependence on flare energy, and its correlation to the occurrence of ΔBLOS. We detected WLE in 44/75 flares and ΔBLOS in 59/75 flares. We find that WLE and ΔBLOS are related, and their locations often overlap between 0% and 60%. Not all locations coincide, thus potentially indicating differences in their origin. We find that the WL area is related to the flare class by a power law, and extend the findings of previous studies, that the WLE is related to the flare class by a power law, to also be valid for C-class flares. To compare unresolved (Sun-as-a-star) WL measurements with our data, we derive a method to calculate temperatures and areas of such data under the blackbody assumption. The calculated unresolved WLE areas improve, but still differ to the resolved flaring area by about a factor of 5-10 (previously 10-20), which could be explained by various physical or instrumental causes. This method could also be applied to stellar flares to determine their temperatures and areas independently.

Keywords: Solar photosphere, Solar flares, Solar magnetic fields, Solar white-light flares
The X-Ray Fundamental Plane of the Platinum Sample, the Kilonovae, and the SNe Ib/c Associated with GRBs. A large fraction of gamma-ray burst (GRB) lightcurves (LCs) show X-ray plateaus. We analyze all GRBs with known redshifts presenting plateaus observed by The Neil Gehrels Swift Observatory from its launch until 2019 August. The fundamental plane relation between the rest-frame time and X-ray luminosity at the end of the plateau emission and the peak prompt luminosity holds for all the GRB classes when selection biases and cosmological evolutions are applied. We have discovered two important findings: (1) a new class of long GRBs with good data coverage: the platinum sample; and (2) the platinum, the SNe-LGRB, and the KN-SGRB samples, yield the smallest intrinsic scatter with σplatinum,GRB-SNe = 0.22 ± 0.10 and σKN-SGRB = 0.24 ± 0.12. The SNe-LGRBs are composed of GRBs associated spectroscopically with the SNe Ib,c, the KN-SGRBs are composed by eight GRBs associated with kilonovae or where there could have been such an association. The highest correlation coefficients are yielded for the SN-LGRB-ABC sample, which includes GRBs spectroscopically associated with SNe Ib/c or with a clear optical bump in the LC resembling the SNe Ib/c, ( ${R}_{\mathrm{SN} \mbox{-} \mathrm{LGRB} \mbox{-} \mathrm{ABC}}^{2}=0.95$ ), the SN-LGRBs ( ${R}_{\mathrm{SN} \mbox{-} \mathrm{LGRB}}^{2}=0.91$ ), and the KN-SGRBs ( ${R}_{\mathrm{KN} \mbox{-} \mathrm{SGRB}}^{2}=0.90$ ) when the redshift evolution is considered. These category planes are reliable candidates to use as cosmological tools. Furthermore, the distance from the gold fundamental plane is a crucial discriminant among classes. In fact, we find that the distributions of the distances of the SNe-LGRB, SNe-LGRB-ABC, KN-SGRB, and SGRB samples from the gold fundamental plane are statistically different from the distribution of the gold GRBs' distances from the gold fundamental plane with and without considering evolution cases.

Keywords: Gamma-ray bursts
Tidal Disruptions of Main-sequence Stars. I. Observable Quantities and Their Dependence on Stellar and Black Hole Mass. This paper introduces a series of papers presenting a quantitative theory for the tidal disruption of main-sequence stars by supermassive black holes. Using fully general relativistic hydrodynamics simulations and MESA-model initial conditions, we explore the pericenter-dependence of tidal disruption properties for eight stellar masses ( $0.15\leqslant {M}_{\star }/{M}_{\odot }\leqslant 10$ ) and six black hole masses ( ${10}^{5}\leqslant {M}_{\mathrm{BH}}/{M}_{\odot }\leqslant 5\times {10}^{7}$ ). We present here the results most relevant to observations. The effects of internal stellar structure and relativity decouple for both the disruption cross section and the characteristic energy width of the debris. Moreover, the full disruption cross section is almost independent of M⋆ for M⋆/M⊙ ≲ 3. Independent of M⋆, relativistic effects increase the critical pericenter distance for full disruption events by up to a factor of ∼3 relative to the Newtonian prediction. The probability of a direct capture is also independent of M⋆; at MBH/M⊙ ≃ 5 × 106 this probability is equal to the probability of a complete disruption. The breadth of the debris energy distribution ΔE can differ from the standard estimate by factors of 0.35 - 2, depending on M⋆ and MBH, implying a corresponding change (∝(ΔE)-3/2) in the characteristic mass-return timescale. We provide analytic forms, suitable for use in both event rate estimates and parameter inference, to describe all these trends. For partial disruptions, we find a nearly universal relation between the star's angular momentum and the fraction of M⋆ remaining. Within the "empty loss-cone" regime, partial disruptions must precede full disruptions. These partial disruptions can drastically affect the rate and appearance of subsequent total disruptions.

Keywords: Black hole physics, Supermassive black holes, Hydrodynamics, Gravitation, Stellar dynamics, Galaxy nuclei, General relativity
Tidal Disruptions of Main-sequence Stars. II. Simulation Methodology and Stellar Mass Dependence of the Character of Full Tidal Disruptions. This is the second in a series of papers presenting the results of fully general relativistic simulations of stellar tidal disruptions in which the stars' initial states are realistic main-sequence models. In the first paper, we gave an overview of this program and discussed the principal observational implications of our work. Here we describe our calculational method, which includes a new method for calculating fully relativistic stellar self-gravity, and provide details about the outcomes of full disruptions, focusing on the stellar mass dependence of the outcomes for a black hole of mass 106 M⊙. We consider eight different stellar masses, from 0.15 M⊙ to 10 M⊙. We find that, relative to the traditional order-of-magnitude estimate rt, the physical tidal radius of low-mass stars (M⋆ ≲ 0.7 M⊙) is larger by tens of percent, while for high-mass stars (M⋆ ≳ 1 M⊙) it is smaller by a factor of 2-2.5. The traditional estimate of the range of energies found in the debris is ≈1.4× too large for low-mass stars, but is a factor of ∼2 too small for high-mass stars; in addition, the energy distribution for high-mass stars has significant wings. For all stars undergoing tidal encounters, we find that mass loss continues for many stellar vibration times because the black hole's tidal gravity competes with the instantaneous stellar gravity at the star's surface until the star has reached a distance from the black hole ∼O(10)rt.

Keywords: Black hole physics, Supermassive black holes, Hydrodynamics, Gravitation, Stellar dynamics, Galaxy nuclei, General relativity
Tidal Disruptions of Main-sequence Stars. III. Stellar Mass Dependence of the Character of Partial Disruptions. In this paper, the third in this series, we continue our study of tidal disruption events of main-sequence stars by a nonspinning 106 M⊙ supermassive black hole. Here we focus on the stellar mass dependence of the outcomes of partial disruptions. As the encounter becomes weaker, the debris mass is increasingly concentrated near the outer edges of the energy distribution. As a result, the mass fallback rate can deviate substantially from a t-5/3 power law, becoming more like a single peak with a tail declining as t-p with p ≃ 2-5. Surviving remnants are spun-up in the prograde direction and are hotter than main-sequence stars of the same mass. Their specific orbital energy is ≃10-3× that of the debris, but of either sign with respect to the black hole potential, while their specific angular momentum is close to that of the original star. Even for strong encounters, remnants have speeds at infinity relative to the black hole potential ≲300 km s-1, so they are unable to travel far out into the galactic bulge. The remnants most deeply bound to the black hole go through a second tidal disruption event upon their first return to pericenter; if they have not thermally relaxed, they will be completely disrupted.

Keywords: Supermassive black holes, Hydrodynamical simulations, Galactic center, Hydrodynamics, Gravitation, Tidal disruption, Stellar dynamics, General relativity
Tidal Disruptions of Main-sequence Stars. IV. Relativistic Effects and Dependence on Black Hole Mass. Using a suite of fully relativistic hydrodynamic simulations applied to main-sequence stars with realistic internal density profiles, we examine full and partial tidal disruptions across a wide range of black hole mass ( ${10}^{5}\leqslant {M}_{\mathrm{BH}}/{M}_{\odot }\leqslant 5\times {10}^{7}$ ) and stellar mass ( $0.3\leqslant {M}_{\star }/{M}_{\odot }\leqslant 3$ ) as larger MBH leads to stronger relativistic effects. For fixed M⋆, as MBH increases, the ratio of the maximum pericenter distance yielding full disruptions ( ${{ \mathcal R }}_{{\rm{t}}}$ ) to its Newtonian prediction rises rapidly, becoming triple the Newtonian value for ${M}_{\mathrm{BH}}=5\times {10}^{7}\,{M}_{\odot }$ , while the ratio of the energy width of the stellar debris for full disruptions to the Newtonian prediction decreases steeply, resulting in a factor of 2 correction at ${M}_{\mathrm{BH}}=5\times {10}^{7}\,{M}_{\odot }$ . We provide approximate formulae that express the relativistic corrections of both ${{ \mathcal R }}_{{\rm{t}}}$ and the energy width relative to their Newtonian approximate estimates. For partial disruptions, we find that the fractional remnant mass for a given ratio of the pericenter to ${{ \mathcal R }}_{{\rm{t}}}$ is higher for larger MBH. These results have several implications. As MBH increases above $\sim {10}^{7}\,{M}_{\odot }$ , the cross section for complete disruptions is suppressed by competition with direct capture. However, the cross-section ratio for partial to complete disruptions depends only weakly on MBH. The relativistic correction to the debris energy width delays the time of peak mass-return rate and diminishes the magnitude of the peak return rate. For ${M}_{\mathrm{BH}}\gtrsim {10}^{7}\,{M}_{\odot }$ , the MBH-dependence of the full disruption cross section and the peak mass-return rate and time is influenced more by relativistic effects than by Newtonian dynamics.

Keywords: Supermassive black holes, Galactic center, Black holes, Gravitation, Tidal disruption, General relativity
The Host Galaxy of OJ 287 Revealed by Optical and Near-infrared Imaging. The BL Lacertae object OJ 287 (z = 0.306) has unique double-peaked optical outbursts every ∼12 yr, and it presents one of the best cases for a small-separation binary supermassive black hole (SMBH) system, with an extremely massive primary $\mathrm{log}({M}_{\mathrm{BH}}/{M}_{\odot })\sim 10.3$ . However, the host galaxy is unresolved or only marginally detected in all optical studies so far, indicating a large deviation from the bulge mass—SMBH mass relation. We have obtained deep, high spatial resolution i-band and K-band images of OJ 287 when the target was in a low state, which enable us to detect the host galaxy. We find the broadband photometry of the host to be consistent with an early-type galaxy with MR = -22.5 and MK = -25.2, placing it in the middle of the host galaxy luminosity distribution of BL Lacertae objects. The central supermassive black hole is clearly overmassive for a host galaxy of that luminosity, but not unprecedented, given some recent findings of other "overmassive" black holes in nearby galaxies.

Keywords: AGN host galaxies, BL Lacertae objects, Supermassive black holes, Elliptical galaxies