Sazuna/UAT_keywords huggingface dataset:
Simultaneous Multiband Photometry of the Early Optical Afterglow of GRB 240825A with Mephisto. Gamma-ray bursts (GRBs) are the most luminous transients in the Universe. The interaction of the relativistic jet with the circumburst medium produces an afterglow and generates multiwavelength emission. In this work, we present simultaneous multiband photometry of GRB 240825A with the Multi-channel Photometric Survey Telescope (Mephisto) and analyze its temporal and spectral properties. The measurement began 128 s after the GRB trigger and continued until the fourth day, when the afterglow essentially diminished and the measured brightness was close to that of the host galaxy. Based on the multiband light curves in the uvgriz bands, we find that the optical flux density satisfies Fν,obs ∝ t‑1.34ν‑2.48 with a spectral index of 2.48, much larger than those of most other GRBs. To reconcile the measured much softer spectral energy distribution (SED) with that predicted by the standard afterglow model, an extra host-galaxy extinction of EB‑V ∼ (0.37–0.57) mag is required. We interpreted this excess as arising from a dense circumburst medium. We further find that the SED of the optical afterglow hardened as the afterglow decayed and the color excess EB‑V decreased ∼0.26 mag from 100 to 3000 s after the GRB trigger. Finally, we analyze the properties of the host galaxy of GRB 240825A based on data from the Sloan Digital Sky Survey, the Pan-STARRS survey, and the HSC-SSP survey. For a host redshift of z = 0.659, the stellar mass and star formation rate of the host galaxy are estimated to be   and  , respectively, pointing to a gas-rich, star-forming, medium-size galaxy.

Keywords: Optical astronomy, Light curves, Gamma-ray bursts
Low-energy Injection and Nonthermal Particle Acceleration in Relativistic Magnetic Turbulence. Relativistic magnetic turbulence has been proposed as a process for producing nonthermal particles in high-energy astrophysics. The particle energization may be contributed by both magnetic reconnection and turbulent fluctuations, but their interplay is poorly understood. It has been suggested that during magnetic reconnection the parallel electric field dominates the particle acceleration up to the lower bound of the power-law particle spectrum, but recent studies show that electric fields perpendicular to the magnetic field can play an important, if not dominant role. In this study, we carry out two-dimensional fully kinetic particle-in-cell simulations of magnetically dominated decaying turbulence in a relativistic pair plasma. For a fixed magnetization parameter σ0 = 20, we find that the injection energy ɛinj converges with increasing domain size to ɛinj ≃ 10 mec2. In contrast, the power-law index, the cut-off energy, and the power-law extent increase steadily with domain size. We trace a large number of particles and evaluate the contributions of the work done by the parallel (W∥) and perpendicular (W⊥) electric fields during both the injection phase and the postinjection phase. We find that during the injection phase, the W⊥ contribution increases with domain size, suggesting that it may eventually dominate injection for a sufficiently large domain. In contrast, on average, both components contribute equally during the postinjection phase, insensitive to the domain size. For high energy (ɛ ≫ ɛinj) particles, W⊥ dominates the subsequent energization. These findings may improve our understanding of nonthermal particles and their emissions in astrophysical plasmas.

Keywords: High energy astrophysics, Astronomical simulations, Plasma astrophysics, Non-thermal radiation sources, Particle astrophysics
Repeating Partial Tidal Encounters of Sun-like Stars Leading to Their Complete Disruption. Stars grazing supermassive black holes on bound orbits may produce periodic flares over many passages, known as repeating partial tidal disruption events (TDEs). Here, we present 3D hydrodynamic simulations of Sun-like stars over multiple tidal encounters. The star is significantly restructured and becomes less concentrated as a result of mass loss and tidal heating. The vulnerability to mass loss depends sensitively on the stellar density structure, and the strong correlation between the fractional mass loss ΔM/M* and the ratio of the central and average density  , which was initially derived in disruption simulations of main-sequence stars, also applies for stars strongly reshaped by tides. Over multiple orbits, the star loses progressively more mass in each encounter and is doomed to a complete disruption. Throughout its lifetime, the star may produce numerous weak flares (depending on the initial impact parameter), followed by a couple of luminous flares whose brightness increases exponentially. Flux-limited surveys are heavily biased toward the brightest flares, which may appear similar to the flare produced by the same star undergoing a full disruption on its first tidal encounter. This places new challenges on constraining the intrinsic TDE rates, which need to take repeating TDEs into account. Other types of stars with different initial density structures (e.g., evolved stars with massive cores) follow distinct evolution tracks, which might explain the diversity of the long-term luminosity evolution seen in recently uncovered repeaters.

Keywords: Supermassive black holes, Tidal disruption, Stellar structures, Time domain astronomy
The Importance of Gas Starvation in Driving Satellite Quenching in Galaxy Groups at z ~ 0.8. We present results from a Keck/DEIMOS survey to study satellite quenching in group environments at z ~ 0.8 within the Extended Groth Strip (EGS). We target 11 groups in the EGS with extended X-ray emission. We obtain high-quality spectroscopic redshifts for group member candidates, extending to depths over 1 order of magnitude fainter than existing DEEP2/DEEP3 spectroscopy. This depth enables the first spectroscopic measurement of the satellite quiescent fraction down to stellar masses of ~109.5M⊙ at this redshift. By combining an infall-based environmental quenching model, constrained by the observed quiescent fractions, with infall histories of simulated groups from the IllustrisTNG100-1-Dark simulation, we estimate environmental quenching timescales (τquench) for the observed group population. At high stellar masses (M⋆ = 1010.5M⊙) we find that   Gyr, which is consistent with previous estimates at this epoch. At lower stellar masses (M⋆ = 109.5M⊙), we find that   Gyr, which is shorter than prior estimates from photometry-based investigations. These timescales are consistent with satellite quenching via starvation, provided the hot gas envelope of infalling satellites is not stripped away. We find that the evolution in the quenching timescale between 0 &lt;z &lt;1 aligns with the evolution in the dynamical time of the host halo and the total cold gas depletion time. This suggests that the doubling of the quenching timescale in groups since z ~ 1 could be related to the dynamical evolution of groups or a decrease in quenching efficiency via starvation with decreasing redshift.

Keywords: Galaxy environments, Galaxy evolution, Galaxy groups, Extragalactic astronomy, Galaxy quenching
From Halos to Galaxies. VI. Improved Halo Mass Estimation for SDSS Groups and Measurement of the Halo Mass Function. In ΛCDM cosmology, galaxies form and evolve in their host dark matter (DM) halos. Halo mass is crucial for understanding the halo–galaxy connection. The abundance-matching (AM) technique has been widely used to derive the halo masses of galaxy groups. However, the quenching of the central galaxy can decouple the coevolution of its stellar mass and DM halo mass. Different halo assembly histories can also result in significantly different final stellar masses of the central galaxies. These processes can introduce substantial uncertainties into the halo masses derived from the AM method, particularly leading to a systematic bias between groups with star-forming centrals (blue groups) and passive centrals (red groups). To improve this, we have developed a new machine learning (ML) algorithm that accounts for these effects and is trained on simulations. Our results show that the ML method eliminates the systematic bias in the derived halo masses for blue and red groups and is, on average, ~one-third more accurate than the AM method. With careful calibrations of observable quantities from simulations and observations from the Sloan Digital Sky Survey (SDSS), we apply our ML model to the SDSS groups to derive their halo masses down to 1011.5M⊙ or even lower. The derived SDSS group halo mass function agrees well with the theoretical predictions, and the derived stellar-to-halo mass relations for both the red and blue groups match well with those obtained from direct weak-lensing measurements. These new halo mass estimates enable more accurate investigation of the galaxy–halo connection and the role of halos in galaxy evolution.

Keywords: Galaxy dark matter halos, Galaxy formation, Galaxy evolution, Galaxies
Tempered Superdiffusive Shock Acceleration at a Perpendicular Shock. A theory for steady-state tempered superdiffusive shock acceleration of energetic particles at a plane perpendicular shock is presented that involves solving analytically a tempered fractional Parker transport equation for perpendicular transport in quasi-2D turbulence. The main predictions of the theory are as follows: (i) Tempered perpendicular superdiffusion (tempered Lévy flights) upstream reduces the effectiveness of classical perpendicular superdiffusion (standard Lévy flights) through a transition toward normal perpendicular diffusion when the particle transport distance upstream surpasses a critical spatial scale. Consequently, the accelerated particle distribution upstream decays spatially as a stretched exponential close to the shock that becomes a power law farther upstream under some conditions (superdiffusion), followed by an exponential rollover (transition to normal diffusion); (ii) Downstream, the accelerated particle distribution for tempered superdiffusion converges to a uniform distribution closer to the shock because of a stronger decay close to the shock compared to classical superdiffusion, and a shift of the peak in the distribution at the shock to just downstream of the shock occurs under some conditions; (iii) The accelerated power-law momentum spectrum at the shock is modulated upstream by the incoming solar wind flow to be a hardened power law instead of featuring an exponential rollover at lower particle momenta as for classical diffusive shock acceleration; and (iv) Tempered superdiffusive shock acceleration tends to be more efficient compared to standard superdiffusive shock acceleration.

Keywords: Interplanetary shocks, Solar energetic particles, Interplanetary turbulence, Solar wind, Non-Gaussianity, Interplanetary particle acceleration
Some Stars Fade Quietly: Varied Supernova Explosion Outcomes and Their Effects on the Multiphase Interstellar Medium. We present results from galaxy evolution simulations with a multiphase interstellar medium (ISM), a mass resolution of 4 M⊙, and a spatial resolution of 0.5 pc. These simulations include a resolved stellar stellar feedback model. Our fiducial run WLM-fid adopts 1051 erg for the supernova (SN) energy. Among the remaining seven simulations, there are two runs where we vary this number by fixing the energy at 1050 erg and 1052 erg (WLM-1e50 and WLM-1e52). Additionally, we carry out one run with variable SN-energy (WLM-variable) and run two simulations where only 10% or 60% of stars explode as SNe with 1051 erg, while the remaining stars do not explode (WLM-60prob and WLM-10prob). We find that the variation in the SN energy, has only minor effects: the star formation rate changes by roughly a factor of 2 compared to WLM-fid, and the strength of the galactic outflows in mass and energy is reduced by 30%, with typical values of ηm ∼ 0.1 and ηe ∼ 0.05 (at a height of 3 kpc after the hot wind is fully decoupled from the galactic ISM). In contrast, the increase and decrease in the canonical SN-energy have a clear impact on the phase structure, with loading factors that are at least 10 times lower/higher and a clear change in the phase structure (the energy loading is normalized self-consistently to the initial mass function averaged explosion energy). We conclude that these modulations are driven not by the minor change in SN-energy but rather by the likelihood of whether or not an event occurs when variable SN energies are applied.

Keywords: Galactic winds, Hydrodynamical simulations, Stellar feedback, Galaxy evolution, Interstellar medium
Increased Surface Temperatures of Habitable White Dwarf Worlds Relative to Main-sequence Exoplanets. Discoveries of giant planet candidates orbiting white dwarf (WD) stars and the demonstrated capabilities of the James Webb Space Telescope bring the possibility of detecting rocky planets in the habitable zones (HZs) of WDs into pertinent focus. We present simulations of an aqua planet with an Earth-like atmospheric composition and incident stellar insolation orbiting in the HZ of two different types of stars—a 5000 K WD and main-sequence K-dwarf star Kepler-62 (K62) with a similar effective temperature—and identify the mechanisms responsible for the two differing planetary climates. The synchronously rotating WD planet's global mean surface temperature is 25 K higher than that of the synchronously rotating planet orbiting K62, due to its much faster (10 hr) rotation and orbital period. This ultrafast rotation generates strong zonal winds and meridional flux of zonal momentum, stretching out and homogenizing the scale of atmospheric circulation, and preventing an equivalent buildup of thick, liquid water clouds on the dayside of the planet compared to the synchronous planet orbiting K62, while also transporting heat equatorward from higher latitudes. White dwarfs may therefore present amenable environments for life on planets formed within or migrated to their HZs, generating warmer surface environments than those of planets with main-sequence hosts to compensate for an ever shrinking incident stellar flux.

Keywords: White dwarf stars, Astrobiology, Planetary climates
The Effect of Stellar Evolution on Dispersal of Protoplanetary Disks: Disk Fraction in Star-forming Regions. We study the effect of stellar evolution on the dispersal of protoplanetary disks by performing one-dimensional simulations of long-term disk evolution. Our simulations include viscous disk accretion, magnetohydrodynamic winds, and photoevaporation as important disk dispersal processes. We consider a wide range of stellar mass of 0.1–7 M⊙ and incorporate the luminosity evolution of the central star. For solar-mass stars, stellar evolution delays the disk dispersal time as the far-ultraviolet (FUV) luminosity decreases toward the main sequence. In the case of intermediate-mass stars, the FUV luminosity increases significantly over a few million years, driving strong photoevaporation and enhancing disk mass loss during the later stages of disk evolution. This highlights the limitations of assuming a constant FUV luminosity throughout a simulation. Photoevaporation primarily impacts the outer regions of the disk and is the dominant disk dispersal process in the late evolutionary stage. Based on the results of a large set of simulations, we study the evolution of a population of star–disk systems and derive the disk fraction as a function of time. We demonstrate that the inclusion of stellar luminosity evolution can alter the disk fraction by several tens of percent, bringing the simulations into closer agreement with recent observations. We argue that it is important to include the stellar luminosity evolution in simulations of the long-term dispersal of protoplanetary disks.

Keywords: Star forming regions, Computational methods, Protoplanetary disks, Stellar evolution
Suzaku Observations of the Cold Front in A3667: A Nonequilibrium Ionization State of the Intracluster Medium. We present a systematic study of the thermodynamic properties of the intracluster medium (ICM), including the plasma conditions in the ICM, in the merging galaxy cluster A3667 using Suzaku. We analyze the X-ray spectra of the ICM between the northwestern and the southeastern radio relics across a prominent cold front in A3667 to search for the ICM in a nonequilibrium ionization (NEI) state. We find that the ICM inside the cold front exhibits an NEI state with an ionization parameter of (2.2 ± 0.4) × 1011 s cm−3 at the 90% confidence level, which is lower than that expected from a collisional ionization equilibrium state of the ICM (i.e., net &gt; 1012 s cm−3). The timescale calculated from the ionization parameter of the ICM inside the cold front is  , which is much shorter than the thermal equilibration timescale. A weak transonic sloshing motion might explain the possibility that the ICM inside the cold front of A3667 is in the NEI state. In addition, the NEI state of the ICM in A3667 seems to be associated with the elongated radio halo bridging the region between the northwestern radio relic and the prominent cold front in A3667 across the cluster center.

Keywords: Galaxy clusters, Intracluster medium, X-ray astronomy
Recovering Pulsar Periodicity from Time-of-arrival Data by Finding the Shortest Vector in a Lattice. The strict periodicity of pulsars is one of the primary ways through which their nature and environment can be studied, and it has also enabled precision tests of general relativity and studies of nanohertz gravitational waves using pulsar timing arrays (PTAs). Identifying such a periodicity from a discrete set of arrival times is a difficult algorithmic problem, In particular when the pulsar is in a binary system. This challenge is especially acute in γ-ray pulsar astronomy, as there are hundreds of unassociated Fermi-LAT sources that may be produced by γ-ray emission from unknown pulsars. Recovering their timing solutions will help reveal their properties and may allow them to be added to PTAs. The same issue arises when attempting to recover a strict periodicity for repeating fast radio bursts (FRBs). Such a detection would be a major breakthrough, providing us with the FRB source's age, magnetic field, and binary orbit. The problem of recovering a timing solution from sparse time-of-arrival data is currently unsolvable for pulsars in unknown binary systems, and incredibly hard even for isolated pulsars. In this paper, we frame the timing recovery problem as the problem of finding a short vector in a lattice and obtain the solution using off-the-shelf lattice reduction and sieving techniques. As a proof of concept, we solve PSR J0318+0253, a millisecond γ-ray pulsar discovered by FAST in a γ-ray-directed search, in a few CPU minutes. We discuss the assumptions of the standard lattice techniques and quantify their performance and limitations.

Keywords: Gamma-ray astronomy, Computational methods, Astronomy data analysis, Pulsars
The Solar and Geomagnetic Storms in 2024 May: A Flash Data Report. In 2024 May, the scientific community observed intense solar eruptions that resulted in a great geomagnetic storm and auroral extensions, highlighting the need to document and quantify these events. This study mainly focuses on their quantification. The source active region (AR; NOAA Active Region 13664) evolved from 113 to 2761 millionths of the solar hemisphere between May 4 and 14. NOAA AR 13664's magnetic free energy surpassed 1033 erg on May 7, triggering 12 X-class flares on May 8–15. Multiple interplanetary coronal mass ejections (ICMEs) were produced from this AR, accelerating solar energetic particles toward Earth. According to satellite and interplanetary scintillation data, at least four ICMEs erupted from AR 13664, eventually overcoming and combining each other. The shock arrival at 17:05 UT on May 10 significantly compressed the magnetosphere down to ≈5.04 R E and triggered a deep Forbush Decrease. GOES satellite data and ground-based neutron monitors confirmed a ground-level enhancement from 2 UT to 10 UT on 2024 May 11. The ICMEs induced exceptional geomagnetic storms, peaking at a provisional Dst index of ‑412 nT at 2 UT on May 11, marking the sixth-largest storm since 1957. The AE and AL indices showed great auroral extensions that located the AE/AL stations into the polar cap. We gathered auroral records at that time and reconstructed the equatorward boundary of the visual auroral oval to 29.°8 invariant latitude. We compared naked-eye and camera auroral visibility, providing critical caveats on their difference. We also confirmed global disturbances of the storm-enhanced density of the ionosphere.

Keywords: Geomagnetic fields, Sunspot groups, Solar flares, Earth ionosphere, Planetary magnetospheres, Aurorae, Solar active regions, Solar coronal mass ejections, Solar storm, Solar particle emission, Cosmic rays
Time-dependent Acceleration and Escape of Charged Particles at Traveling Shocks in the Near-Sun Environment. Current multi-spacecraft in situ measurements allow for the investigation of the time evolution of energetic particles at interplanetary shocks (IPs) at small (≲0.1 au) heliocentric distances. The energy spectrum of accelerated particles at IPs was shown by a previous 1D transport model that includes both self-excited plus preexisting turbulence and a term representing the escape of particles from the system to gradually steepen as a result of a finite acceleration-to-escape timescales ratio; such a model was found in excellent agreement with the entire sample of the ground-level enhancement spectra of solar cycle 23. We solve the time-dependent case of such a model in the case of diffusion dominated by preexisting turbulence. The average timescale for particle acceleration at various heliocentric distances, from 1 au down to the inner heliosphere (&lt;0.1 au), is shorter than in the no-escape case, as higher energy particles have a shorter time to accelerate before completely leaving the system into the upstream medium. A simple scaling with time of the time-dependent spectrum is provided. We compare the "nose" structure at a few ∼100s keV protons first measured in situ by Parker Solar Probe in crossing the very fast 2022 September 5 shock at 0.07 au; we find that the nose is reasonably well explained by a lack of the highest energy particles not yet produced by the young shock by both our model and the no-escape version.

Keywords: Solar energetic particles, Solar wind, Interplanetary shocks
Cosmic Chronometers, Pantheon+ Supernovae, and Quasars Favor Coasting Cosmologies over the Flat ΛCDM Model. We test and compare coasting cosmological models with curvature parameters   in   units and the flat ΛCDM model by fitting them to cosmic chronometers (CCs), the Pantheon+ sample of Type Ia supernovae (SNe), and standardized quasars (QSOs). We used the emcee code for fitting CC data, a custom Markov Chain Monte Carlo implementation for SNe and QSOs, and Anderson–Darling tests for normality on normalized residuals for model comparison. Best-fit parameters are presented, constrained by data within redshift ranges z ≤ 2 for CCs, z ≤ 2.3 for SNe, and z ≤ 7.54 for QSOs. Coasting models, particularly the flat coasting model, are generally favored over the flat ΛCDM model. The overfitting of the flat ΛCDM model to Pantheon+ SNe and the large intrinsic scatter in QSO data suggest a need to refine error estimates in these data sets. We also highlight the seemingly fine-tuned nature of either the CC data or Ωm,0 in the flat ΛCDM model to an H1 = H0 coincidence when fitting H(z) = H1z + H0, a natural feature of coasting models.

Keywords: Cosmology, Cosmological models, Observational cosmology, Cosmological parameters