Sazuna/UAT_keywords huggingface dataset:
A "Faux-Shock" Method for Hybrid Simulations of Astrophysical Shocks. We demonstrate a novel setup for hybrid particle-in-cell simulations designed to isolate the physics of the shock precursor over long time periods for significantly lower computational cost than previous methods. This is achieved using a "faux-shock" or shock-like boundary condition on one edge of our simulation domain such that particles that interact with the boundary either pass through it or are reflected off of it with a change in momentum that mimics scattering in the downstream. We show that our faux-shock setup reproduces the same fluid quantities and phase spaces as traditional shock simulations, including those which could otherwise only be done in 3D, with higher particle resolution and for reduced computational cost. While the method involves an assumed boundary condition, it nonetheless captures the essential physics of interest, establishing it as a reliable and efficient tool for future self-consistent studies of instabilities driven by cosmic rays in a shock upstream medium.

Keywords: Astronomical simulations, Plasma astrophysics, Shocks, Particle astrophysics, Cosmic rays
SN 2023syz and SN 2025cbj: Two Type IIn Supernovae Associated with IceCube High-energy Neutrinos. Type IIn supernovae (SNe IIn) are a subclass of core-collapse SNe in which strong interactions occur between the ejecta and dense circumstellar material, creating ideal conditions for the production of high-energy neutrinos. This makes them promising candidate sources of neutrinos. In this work, we conduct an association study between 163 SNe IIn observed by the Zwicky Transient Facility and 138 neutrino alert events detected by the IceCube Neutrino Observatory. After excluding alerts with poor localization, we find two SNe that are spatiotemporally coincident with neutrino events. IC 231027A and IC 250421A coincide with the positions of SN 2023syz and SN 2025cbj, respectively, within their localization uncertainties, and the neutrino arrival times are delayed by 38 days and 61 days relative to the discovery times of the corresponding SNe. Using Monte Carlo simulations, we estimate that the probability of two such events occurring by chance in our sample is p ∼ 0.67%, suggesting that they may originate from genuine physical associations, though the result is not yet statistically significant. Our model calculations, however, indicate that the likelihood of a neutrino originating from IC 231027A is low, implying that the association between IC 231027A and SN 2023syz is likely coincidental. Nevertheless, under optimistic parameters, the probability of detecting a neutrino from the whole SNe IIn sample could reach ≳6%, indicating that detecting neutrino emission from the SNe population may be possible. Our study provides a systematic analysis, combining statistical analysis and model calculations, to assess whether interacting supernovae can serve as potential sources of neutrino emission.

Keywords: Neutrino astronomy, Supernova neutrinos, High energy astrophysics
The Distribution of Earth-impacting Interstellar Objects. In this paper we calculate the expected orbital elements, radiants, and velocities of Earth-impacting interstellar objects. We generate a synthetic population of ∼1010 interstellar objects with M-star kinematics in order to obtain ∼104 Earth impactors. The relative flux of impactors arriving from the direction of the solar apex and the Galactic plane is enhanced by a factor of ∼2 relative to the mean. The fastest impactors also arrive from these directions, although Earth impactors are generally slower than objects in the overall population. This is because the Earth-impacting subset contains a higher fraction of low-eccentricity hyperbolic objects, which are more strongly affected by gravitational focusing. Earth-impacting interstellar objects are more likely to have retrograde orbits close to the ecliptic plane. A selection effect makes the inclination distribution of Earth-impacting interstellar objects uniform (sinusoidal) at low (high) perihelion distances. In turn, low-perihelion impactors have a higher impact probability towards the ecliptic plane. The overall impactor population therefore exhibits an intermediate inclination distribution between uniform and sinusoidal. In turn, low-perihelion impactors have a higher impact probability towards the ecliptic plane. The highest-velocity impacts are most likely to occur in the spring when the Earth is moving towards the solar apex. However, impacts in general are more likely to occur during the winter when the Earth is located in the direction of the antapex. Interstellar objects are more likely to impact the Earth at low latitudes close to the equator, with a slight preference for the Northern Hemisphere due to the location of the apex. These distributions are independent of the assumed interstellar object number density, albedos, and size─frequency distribution and are publicly available.

Keywords: Comets, Meteors, Asteroids, Interstellar objects
A Systematic Search for Active Galactic Nuclei Obscuration Variability in the Chandra Archive. The nature of the obscuring material in active galactic nuclei (AGN) can be studied by measuring changes in the line-of-sight column density, NH,LOS, over time. This can be accomplished by monitoring AGN over long periods of time and at all timescales. However, this can only be done for a few selected objects as it is resource intensive. Therefore, the best option currently is to focus on population statistics based on the available archival data. In this work, we study 79 Seyfert 1 and Seyfert 2 galaxies from the Million Quasars (or Milliquas) catalog to estimate a lower limit on the fraction of sources in the local Universe (z &lt; 0.1) that display spectral variability among observations. We find that 43 sources (54% ± 11%) show indications of NH,LOS variability at 90% confidence level. Interestingly, we also find that the variable fraction is similar for both Seyfert 1 ( fSy1∼61−15+13 %) and Seyfert 2 (fSy2 ∼ 47% ± 15%) galaxies. The slightly higher fSy1 fraction could be due to either a physical difference in the obscurers or the higher data quality in the Seyfert 1 population. We also search for potential dependencies on the timescale between variable and nonvariable observation pairs within a given source. In agreement with previous studies, we find evidence that more variability occurs on longer timescales than on shorter timescales. We present the 43 variable sources as a promising sample for future NH variability studies.

Keywords: Seyfert galaxies, Active galactic nuclei, X-ray active galactic nuclei
A Deep Learning Approach for Automated Total Sunspot Number Estimation. Accurate sunspot number estimation is essential for understanding the long-term evolution of solar activity and its impact on space weather. Sunspot numbers have been manually determined, leading to inconsistencies and observer-dependent biases. To address this, the World Data Center Sunspot Index and Long-term Solar Observations (WDC-SILSO) aggregates data from a global network of observatories to estimate the daily total sunspot number, enabling cross-validation and calibration across simultaneous observations. This study proposes a novel deep learning framework for automated total sunspot number calculation using solar full-disk continuum images from the Solar Dynamics Observatory. The method integrates U-Net for sunspot segmentation, K-means clustering for distinguishing umbrae from penumbrae, and You Only Look Once model for sunspot group detection. The selection of image-processing thresholds and neural network hyperparameters is optimized with respect to WDC-SILSO reference values during training. The results demonstrate a high correlation of 0.97 between the estimated and the WDC-SILSO daily total sunspot numbers. Furthermore, the framework offers a scalable approach suitable for future high-resolution solar observations.

Keywords: Sunspot number
Einstein@Home All-sky "Bucket" Search for Continuous Gravitational Waves in LIGO O3a Public Data. We present results from the most sensitive all-sky search to date for continuous gravitational waves with frequencies 30.0 Hz ≤ f ≤ 250.0 Hz and frequency derivatives  −2.7×10−9Hzs−1≤ḟ≤0.2×10−9  Hz s−1. We deploy this search on the Einstein@Home volunteer-computing project and on three supercomputer clusters. At the end of a multistage approach there are four surviving candidates: three from "hardware injections," i.e., signals "added" by moving the instruments' mirrors, and one due to line disturbances in the data. The high sensitivity of our search enabled the first-ever detection of hardware injection 11. We set upper limits on the gravitational wave amplitude h0, and translate these to upper limits on the neutron star ellipticity and on the r-mode amplitude. The most stringent upper limits are at 173 Hz with h0 = 6.5 × 10−26, at the 90% confidence level, which improve by about 70% with respect to the LIGO-Virgo-KAGRA Collaboration's most stringent O3 upper limits, and might well be competitive with results from O4 searches.

Keywords: Gravitational wave astronomy, Neutron stars, Gravitational waves
How Accurately Can Obscured Galaxy Luminosities Be Measured Using Spectral Energy Distribution Fitting of Near- through Far-infrared Observations?. Infrared-luminous galaxies are important sites of stellar and black hole mass assembly at most redshifts. Their luminosities are often estimated by fitting spectral energy distribution (SED) models to near- to far-infrared data, but the dependence of these estimates on the data used is not well understood. Here, using observations simulated from a well-studied local sample, we compare the effects of wavelength coverage, signal-to-noise ratio, flux calibration, angular resolution, and redshift on the recovery of starburst, active galactic nucleus (AGN), and host luminosities. We show that the most important factors are wavelength coverage that spans the peak in a SED, and dense wavelength sampling. Such observations recover starburst and AGN infrared luminosities with systematic bias below 20%. Starburst luminosities are best recovered with far-infrared observations, while AGN luminosities are best recovered with near- and mid-infrared observations, though the recovery of both are enhanced with near/mid-infrared and far-infrared observations, respectively. Host luminosities are best recovered with near/far-infrared observations, but are usually biased low, by ≳20%. The recovery of starburst and AGN luminosity is enhanced by observing at high angular resolution. Starburst-dominated systems show more biased recovery of luminosities than do AGN-dominated systems. As redshift increases, far-infrared observations become more capable and mid-infrared observations less capable at recovering luminosities. Our results highlight the transformative power of a far-infrared instrument with dense wavelength coverage, from tens to hundreds of microns, for studying infrared-luminous galaxies. We tabulate estimates of systematic bias and random error for use with JWST and other observatories.

Keywords: Far infrared astronomy
Explaining the Origin of TeV Gamma Rays from M87 during High and Low States. The detection of very-high-energy gamma rays from M87 can provide crucial insights into particle acceleration and radiation mechanisms in jets. The recent observations by the Large High Altitude Air Shower Observatory detector extend the energy range of TeV gamma-ray astronomy, and also the variability study to the TeV energy domain. We have modeled the low state and flare state multiwavelength spectral energy distributions of M87 within a time-dependent framework. In our model, the low state gamma-ray flux results from the emissions from the subparsec and the kiloparsec scale jets of M87, whereas the flare state gamma-ray flux is mainly produced in the subparsec scale jet. We have shown that the spectral and temporal features of the TeV gamma-ray spectrum of M87 are consistent with this two-zone model, where the contribution from the subparsec scale jet significantly increases during the flare state.

Keywords: Gamma-ray astronomy, Active galactic nuclei, High energy astrophysics
Gray Spectral Variability in Three Brown Dwarfs Observed by HST/WFC3 Time-series Observations. The L/T transition is a critical evolutionary stage for brown dwarfs and self-luminous giant planets. L/T transition brown dwarfs are more likely to be spectroscopically variable, and their high-amplitude variability probes distributions in their clouds and chemical makeup. This paper presents Hubble Space Telescope Wide Field Camera 3 spectral time-series data for three variable L/T transition brown dwarfs and compares the findings to the highly variable benchmark object 2MASS J2139. All four targets reveal significant brightness variability between 1.1 and 1.65 μm but show a difference in wavelength dependence of the variability amplitude. Three of our targets do not show significant decrease in variability amplitude in the 1.4 μm water absorption band commonly found in previous studies of L/T transition brown dwarfs. Additionally, at least two brown dwarfs have irregular-shaped, nonsinusoidal light curves. We create heterogeneous atmospheric models by linearly combining SONORA Diamondback model spectra, comparing them with the observations, and identifying the optimal effective temperature, cloud opacity, and cloud coverage for each object. Comparisons between the observed and model color─magnitude variations that trace both spectral windows and molecular features reveal that the early-T dwarfs likely possess heterogeneous clouds. The three T dwarfs show different trends in the same color─magnitude space, which suggests secondary mechanisms driving their spectral variability. This work broadens the sample of L/T transition brown dwarfs that have detailed spectral time-series analysis and offers new insights that can guide future atmospheric modeling efforts for both brown dwarfs and exoplanets.

Keywords: Brown dwarfs, Atmospheric clouds, Hubble Space Telescope, Time series analysis, Atmospheric variability
The Low-mass and Structured Stellar Halo of M83 Argues Against a Merger Origin for Its Starburst and Extended Neutral Hydrogen Disk. A merger origin has been suggested for M83's massive, metal-rich extended H I disk and nuclear starburst. We observe M83's stellar halo to test this idea. We train nearest-neighbor star─galaxy separation on wide-area Subaru imaging with Hubble Space Telescope data to map M83's halo in resolved stars. We find that M83 has an extended, very low-density smooth stellar halo of old and metal-poor [M/H] ∼ −1.15 RGB stars with a mass between 15 and 40 kpc of  log10M∗,15−40,maj/M⊙=8.02±0.10 . In addition to M83's well-known Northern Stream, our ground-based Subaru imaging reveals a new stream to M83's south, which modeling suggests could be its trailing arm. The combined stream masses are  log10Mstream/M⊙=7.93±0.10 , with metallicity [M/H] = −1.0 ± 0.2. The stream progenitor was only recently accreted, as its stellar populations suggest that it formed stars until 2.1 ± 1.3 Gyr ago. M83 lies on the stellar halo mass─metallicity correlation seen for other Milky Way─mass galaxies, albeit with low stellar halo mass. We infer a total accreted mass of  log10M*,accreted/M⊙=8.78−0.28+0.22 , with the most massive past merger having  log10M*,dom/M⊙=8.5±0.3 . We identify plausible M83 analogs in TNG-50 with similar stellar halos, finding that while a recent accretion can create a prominent stellar stream, such accretions do not trigger starburst activity, nor do they deliver enough gas to form M83's extended H I disk. We conclude that other nonmerger mechanisms, such as secular evolution or accretion of gas from the intergalactic medium, are likely to be responsible for M83's remarkable properties. *This research is based in part on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has the cultural, historical, and natural significance in Hawaii.

Keywords: Galaxy nuclei, Galaxy stellar halos, Galaxy evolution, Galaxy mergers, Red giant stars, Galaxies
JCMT <SUP>12</SUP>CO J = 3─2 Observations of Tycho's Supernova Remnant: Constraints on the Environmental Gas Properties. Recent observations suggest that Tycho's supernova remnant (SNR; SN 1572) is expanding into a cavity wall of molecular clouds (MCs), which decelerate the SNR and influence its multiwavelength morphology. To constrain the physical properties of environmental MCs and search for heated gas, we perform a James Clerk Maxwell Telescope 12CO J = 3─2 observation and compare with previous 12CO J = 2─1, 12CO J = 1─0 and 13CO J = 1─0 data. We present the 12CO J = 3─2 map toward Tycho and show that the 12CO J = 3─2 spatial distribution and line profiles are similar to those of the lower-J CO lines. By comparing the multiple transitions of CO and the RADEX models, we constrain the physical properties of molecular gas surrounding Tycho: the northern cloud has a molecular column density of N(H2) = 0.5─4.5 × 1022 cm−2, while other regions have N(H2) = 0.2─3.9 × 1021 cm−2; the kinetic temperatures Tk of these clouds are in the range of 9─22 K, and the volume densities n(H2) are 20─700 cm−3. We also discuss the difficulty in finding hot molecular gas shocked by such a young SNR. We estimate that the shocked molecular layer can be as thin as 0.003 pc, corresponding to 0 .″ 2 at the distance of 2.5 kpc, which is 2 orders of magnitude smaller than the angular resolution of current CO observations. Therefore, our molecular observations are largely insensitive to the thin shocked gas layer; instead, they detect the environmental gas.

Keywords: Interstellar molecules, Supernova remnants, Molecular clouds, Interstellar medium
The ALMA Survey of 70 µm Dark High-mass Clumps in Early Stages (ASHES). XIII. Core Mass Function, Lifetime, and Growth of Prestellar Cores. The core mass function (CMF) of prestellar cores is essential for understanding the initial conditions of star and cluster formation. However, the universality of the CMF and its relationship to the initial mass function (IMF) remain unclear. We study the CMF in the earliest stage of high-mass star formation using 461 prestellar core candidates and 254 protostellar cores as a part of the ALMA Survey of 70 µm Dark High-mass Clumps in Early Stages (ASHES). We find that prestellar core candidates tend to have lower masses than protostellar cores. We also find that the lifetime of prestellar cores is several times longer than the freefall time, although it approaches the freefall time as the core mass increases. The CMF, including both protostellar and prestellar cores, has a power-law slope of −2.05 ± 0.04, shallower than Salpeter's IMF slope of −2.35. Conversely, the CMF of gravitationally bound, prestellar cores has a steeper slope (−2.32 ± 0.30), indistinguishable from Salpeter's slope. This finding is consistent with observations in both low-mass star-forming regions and high-mass protoclusters, implying a universal core formation mechanism. The protostellar CMF with a larger maximum core mass can be reproduced by the prestellar CMF when an external gas infall is considered. The inferred mass infall rate is higher than the Bondi─Hoyle─Lyttleton accretion rate and follows a shallower mass dependence (smaller power-law index), more consistent with the tidal-lobe accretion. This may contribute to the evolution of CMFs seen in later stages.

Keywords: Star forming regions, Star formation, Radio interferometers, Infrared dark clouds
Discovery of an X-Ray Luminous Radio-loud Quasar at z = 3.4: A Possible Transitional Super-Eddington Phase. We report the multiwavelength properties of eROSITA Final Equatorial Depth Survey (eFEDS) J084222.9+001000 (hereafter ID830), a quasar at z = 3.4351, identified as the most X-ray luminous radio-loud quasar in the eFEDS field. ID830 shows a rest-frame 0.5─2 keV luminosity of  log(L0.5−2keV/ergs−1)=46.20±0.12 , with a steep X-ray photon index (Γ = 2.43 ± 0.21), and a significant radio counterpart detected with the Very Large Array FIRST 1.4 GHz and Very Large Array Sky Survey 3 GHz bands. The rest-frame UV to optical spectra from Sloan Digital Sky Survey and Subaru/MOIRCS J band show a dust-reddened quasar feature with AV = 0.39 ± 0.08 mag, and the expected bolometric active galactic nuclei luminosity from the dust-extinction-corrected UV luminosity reaches Lbol,3000Å = (7.62 ± 0.31) × 1046 erg s−1. We estimate a black hole mass of MBH = (4.40 ± 0.72) × 108 M⊙ based on the Mg IIλ2800 emission-line width, and Eddington ratios from the dust-extinction-corrected UV continuum luminosity and X-ray luminosity that reach λEdd,UV = 1.44 ± 0.24 and λEdd,X = 12.8 ± 3.9, respectively, both indicating super-Eddington accretion. ID830 shows a high ratio of UV to X-ray luminosities, αOX = −1.20 ± 0.07 (or αOX = −1.42 ± 0.07 after correcting for jet-linked X-ray excess), higher than quasars and little red dots in the super-Eddington phase with similar UV luminosities, with αOX &lt; −1.8. Such a high αOX suggests the coexistence of a prominent radio jet and X-ray corona in this high-Eddington-accretion phase. We propose that ID830 may be in a transitional phase after an accretion burst, evolving from a super-Eddington to a sub-Eddington state, which could naturally describe the high αOX.

Keywords: Supermassive black holes, Active galactic nuclei, Radio jets
Hybrid Morphology Radio Sources from the MeerKAT Absorption Line Survey (MALS): Radio, Mid-infrared, and Environmental Characteristics. Hybrid morphology radio sources (HyMoRSs) are a rare subclass of radio galaxies that display a Fanaroff─Riley type I (FR I) morphology on one side of the central supermassive black hole and a type II (FR II) morphology on the other. In this study, we report the discovery of 36 new HyMoRSs, marking the largest collection of such sources in the southern sky to date, using data obtained from the MeerKAT absorption line survey (MALS). The identified HyMoRSs exhibit moderate radio luminosities in the range 9.9 × 1023─5.7 × 1025 W Hz−1, with a median value of 4.4 × 1024 W Hz−1 at 1.4 GHz, and are located within the redshift range 0.04 &lt; z &lt; 1.34. In this work, we show for the first time that the two lobes of HyMoRSs exhibit no statistically significant difference in their spectral indices. We also investigate the mid-infrared properties and environments of their host galaxies. Notably, 9 out of the 36 sources are situated near the centers of galaxy clusters, including one with giant radio jets that extend over 811 kpc. Our analysis reveals that the majority of HyMoRSs are hosted by actively star-forming galaxies that exhibit elevated star formation rates. Furthermore, our findings suggest that HyMoRSs may arise from FR II jets being deflected by a dense, cluster-like environment, along with orientation effects that make one jet appear FR I-like. As our candidates are selected through visual inspection of MALS radio maps, higher-resolution follow-up observations are still necessary to confirm the nature of their morphologies.

Keywords: Active galaxies, Active galactic nuclei, Radio continuum emission, Radio astronomy, Radio sources