Sazuna/UAT_keywords huggingface dataset:
Transient Gamma Rays from the 2021 Outburst of the Recurrent Nova RS Ophiuchi: The Effect of Gamma-Ray Absorption. In 2021, RS Ophiuchi was the first nova to be detected in the very-high-energy (TeV) gamma-ray domain, directly testifying to efficient acceleration of charged particles up to at least the TeV range at the nova shock. Surprisingly, the TeV gamma-ray signal peaks ∼2 days after the GeV signal, and the origin of this delay has still not been clearly understood. We investigate the possibility that this delay is due to the effect of gamma-ray absorption resulting from interactions between gamma rays and optical photons copiously emitted during the outburst. We model particle acceleration at a nova shock to obtain the gamma-ray emission produced in interactions between the accelerated particles and the shocked gas. The effect of gamma-ray absorption is then included in detail using the radiative transfer equation. We find that this can naturally account for the delay between the peaks of GeV and TeV gamma-ray lightcurves. This result emphasizes the importance of gamma-ray absorption for interpreting gamma-ray observations of novae in the TeV range, which, in turn, demonstrates the necessity of a multiwavelength view for unraveling the underlying physics of particle acceleration in these systems.

Keywords: Shocks, Gamma-ray transient sources, Recurrent novae
A Unified Model of Cosmic-Ray Propagation and Radio Extreme Scattering Events from Intermittent Interstellar Structures. Intermittent magnetic structures are a plausible candidate for explaining cosmic-ray (CR) diffusion rates derived from observed CR energy spectra. Independently, studies of extreme scattering events (ESEs) of radio quasars and pulsar scintillation have hinted that very straight, large aspect ratio magnetic current sheets may be responsible for the localized large scattering of radio waves. The required shortest axis of the typical structures producing ESEs is of the same scale (∼au) as the gyroradii of ∼GeV CRs. In this Letter, we propose that the same magnetic/density sheets can produce large scattering of both CRs and radio waves. We demonstrate that the geometry and volume-filling factor of the sheets derived from quasar ESEs can explain the observed mean free path of GeV CRs without introducing free parameters. The model places constraints on the sheet geometry, such as straightness and large aspect ratio, and assumes that the statistics of the sheets are similar throughout the Galactic volume. We therefore discuss observational tests of the sheet model, which includes observations of echoes in pulsars and fast radio bursts, gravitationally lensed quasars, the distribution of ESE durations, and spatial correlations between ESE events and rotation measure fluctuations. Such tests will be enabled by upcoming wide-field radio instruments, including the Canadian Hydrogen Observatory and Radio-transient Detector and Deep Synoptic Array 2000 Antennas.

Keywords: Magnetohydrodynamics, Radio transient sources, High energy astrophysics, Quasars, Plasma astrophysics, Pulsars, Interstellar magnetic fields, Interstellar medium, Interstellar scintillation, Interstellar scattering, Radio sources, Cosmic rays
Evidence for Intrinsic Galaxy Alignments in Ellipticity Autocorrelations Out to 100 h<SUP>‑1</SUP> Mpc from SDSS Galaxies with DESI Imaging. Measuring the autocorrelation of galaxy shapes, known as the intrinsic–intrinsic (II) correlation, is important for both cosmology and understanding the formation of massive elliptical galaxies. However, such measurements are significantly more challenging than those of the cross correlation with galaxy density (GI correlation) due to the much lower signal-to-noise ratio. In this Letter, we report the first observational evidence for large-scale intrinsic alignments measured from the ellipticity autocorrelations, extending out to 100 h‑1 Mpc. From the Sloan Digital Sky Survey (SDSS) and SDSS-III Baryon Oscillation Spectroscopic Survey, we analyze, over the redshift range 0.16 ≤ z ≤ 0.70, luminous red galaxy, LOWZ, and CMASS galaxy samples, the latter two of which are crossmatched with high-quality Dark Energy Spectrograph Instrument imaging data. By expanding one of the two II correlation functions, II(‑), in terms of the associated Legendre polynomials, we effectively isolate the line-of-sight projection effects and enhance the signal. The resulting correlation for all three samples exhibits a clear power-law form. We also show that jointly analyzing the two II correlations, II(+) and II(‑), increases the detection significance by ∼10%, even though both are derived from the same E-mode power spectrum. Importantly, this measurement opens a new observational window for probing signals uniquely encoded in shape autocorrelations, such as tensor perturbations from the gravitational waves. Our analysis establishes a practical framework for extracting such effects.

Keywords: Observational cosmology, Elliptical galaxies, Redshift surveys, Large-scale structure of the universe
The Potential Danger to Satellites due to Ejecta from a 2032 Lunar Impact by Asteroid 2024 YR<SUB>4</SUB>. On 2032 December 22, the 60 m diameter asteroid 2024 YR4 has a 4% chance of impacting the Moon. Such an impact would release 6.5 MT TNT equivalent energy and produce a ∼1 km diameter crater. We estimate that up to 108 kg of lunar material could be liberated in such an impact by exceeding lunar escape speed. The current overall probability is about 1% that the asteroid will impact the Moon at a location such that more than 10% of the ejected material would accrete to the Earth on timescales of a few days. If this were to occur, the lunar-ejecta-associated particle fluence at 0.1–10 mm sizes could produce up to several years of equivalent background meteoroid impact exposure to satellites in near-Earth space late in 2032. Our results demonstrate that planetary defense considerations should be more broadly extended to cislunar space and not confined solely to near-Earth space.

Keywords: Near-Earth objects, Asteroids, Small Solar System bodies, The Moon, Solar system, Natural satellites (Solar system)
Peekaboo: Secular Resonances from Evolving Stellar Oblateness Impede Transit Detections. Secular resonances in exoplanet systems occur when two or more planets have commensurabilities in the precession rates of their orbital elements, causing an exchange of angular momentum between them. The stellar gravitational quadrupole moment, which evolves over time due to stellar spin-down over the first ∼100 Myr, causes these resonances to sweep through the parameter space (of masses and semimajor-axis ratios), affecting a wider variety of systems than when spin-down is neglected. The angular momentum exchange in these resonances typically aligns the outer planets' orbits together while misaligning the innermost planet from its companions. Here, we explore how resonance-induced (mis)alignments between planets affect the transit outcome. We use the three-planet Kepler-619 system as a concrete case study that is relatively likely (approximately 1:1 odds) to have undergone a sweeping resonance. Consequently, if the outer planets are initially misaligned, a sweeping-resonance-induced push toward alignment in the outer planets' orbits substantially increases the probability that they are observed transiting together. However, the resulting misalignment of the innermost planet from its outer companions reduces the overall probability that Kepler-619 is observed as a multiplanet transiting system when considering any pair of planets or all three together. This implies that sweeping resonances (which may occur in 20% of systems) have a deleterious effect on the transiting exoplanet sample, suppressing the detection of multiplanet transiting systems in favor of apparent single-planet systems.

Keywords: Exoplanet detection methods, Stellar structures, Exoplanets, Star-planet interactions, Transit photometry
Temperatures of Jupiter's Upper Atmosphere: The Role of the Planetary Magnetic Field. The primary source of heating in the upper atmospheres (thermospheres) of giant planets has been the subject of long debate. The conundrum (or "energy crisis") consists in observed thermosphere temperatures at low and midlatitudes exceeding values expected from solar heating by several hundred kelvins, suggesting the presence of another energy source. Several theories have been proposed to explain the high temperatures, from heating by upward-propagating gravity or acoustic waves to heating of auroral regions by magnetosphere–atmosphere coupling. While auroral heating provides sufficient energy, the problem becomes one of global energy redistribution. On a rapidly rotating planet, Coriolis forces act to "trap" auroral energy in the polar regions, heating up the poles but leaving the equator cold. On Saturn, the redistribution of energy from poles to equator was recently achieved by invoking Rayleigh drag, possibly related to atmospheric gravity or acoustic waves. Using a new general circulation model of Jupiter, we reproduce well the observed low and midlatitude thermosphere temperatures without the need to invoke Rayleigh drag. Instead, the planet's magnetic field is strong enough to cause significant ion drag and slowing down zonal winds in the nonauroral thermosphere and allow global energy redistribution. This distinguishes Jupiter from Saturn and most likely the other gas giant planets in our solar system may have implications on extrasolar planets with strong magnetic fields as well.

Keywords: Planetary ionospheres, Theoretical models, Planetary atmospheres, Jupiter, Planetary science, Planetary magnetospheres
Probing Thin Winds in Massive OB Stars of the SMC with JWST/NIRSPEC Brα Spectroscopy. Mass loss is a key physical process in the evolution of massive stars, the impact of which propagates into galactic evolution, population synthesis models, the interpretation of high-redshift galaxies, and explosive events such as supernovae. However, there are currently substantial uncertainties in the low-metallicity, low-luminosity thin wind regime where classical diagnostics (Hα and ultraviolet, UV, P Cygni profiles) yield wind momenta that are 1 to 2 orders of magnitude below prescriptions implemented by default in most evolutionary models. Here, we present spectra of the mass-loss diagnostic line Brα in 15 OB-type stars in the Small Magellanic Cloud obtained using the Near Infrared Spectrograph on the James Webb Space Telescope. The line profile morphology, recovered by virtue of the outstanding signal-to-noise ratio of the data and the avoidance of regions with nebular emission, is consistent with predictions based on previous mass-loss rate estimates from optical and UV spectroscopy. Moreover, an initial spectroscopic analysis of sources covering the thin wind regime confirms the low mass-loss rates, indicates a change of slope in the wind-momentum─luminosity relation in this regime with respect to high-luminosity objects, and strengthens the abovementioned discrepancies with commonly used wind-momentum prescriptions.

Keywords: Infrared spectroscopy, Small Magellanic Cloud, OB stars, Stellar physics, Stellar winds, James Webb Space Telescope
UNCOVER/MegaScience: No Evidence of Environmental Quenching in a z ∼ 2.6 Protocluster. Environmental quenching—where interactions with other galaxies and/or the intracluster medium suppress star formation in low-mass galaxies—has been well established as the primary driver behind the formation of the red sequence for low-mass galaxies within clusters at low redshift (z &lt; 1). However, it remains unclear whether these mechanisms are active at higher redshifts in protocluster environments that are not yet fully virialized. In large part, this regime has remained unexplored due to observational limitations; however, JWST has recently opened a new window into the role of environmental quenching on low-mass (log(M⋆/M⊙) &lt; 9.0) galaxies at cosmic noon (2 &lt; z &lt; 3). Here, we leverage the deep imaging and R ∼ 15 spectrophotometry enabled by the 20 band JWST/NIRCam data from the UNCOVER and MegaScience programs to examine environmental quenching in a newly discovered z ≈ 2.58 protocluster. We compare the star formation histories of 19 low-mass quiescent galaxies in the protocluster to a matched sample of 18 in the field and find no significant differences. This similarity extends to galaxy sizes and quenched fractions, which also show no significant differences between the two environments across the full stellar mass range (8.5 &lt; log(M⋆/M⊙) ≤ 11.0). This indicates that the protocluster has not yet accelerated quenching relative to the field and is consistent with expectations that z &gt; 2 protoclusters have yet to virialize and develop a dense enough environment required to efficiently quench low-mass galaxies.

Keywords: Galaxy environments, Protoclusters, James Webb Space Telescope, Galaxy evolution, Extragalactic astronomy, Galaxy quenching
SLICE: SPT-CL J0546-5345—A Prominent Strong-lensing Cluster at z = 1.07. Massive galaxy clusters act as prominent strong lenses. Due to a combination of observational biases, cluster evolution, and lensing efficiency, most of the known cluster lenses lie typically at zl ∼ 0.2─0.7, with only a few prominent examples at higher redshifts. Here we report the first strong-lensing analysis of the massive galaxy cluster SPT-CL J0546-5345 at a redshift zl = 1.07. This cluster was first detected through the Sunyaev─Zel'dovich effect, with a high estimated mass for its redshift of M200,c = (7.95 ± 0.92) × 1014 M⊙. Using recent JWST/NIRCam and archival Hubble Space Telescope imaging, we identify at least 10 secure and 6 candidate sets of multiply imaged background galaxies, which we use to constrain the mass distribution in the cluster. We derive effective Einstein radii of θE = 18 .″ 1 ± 1 .″ 8 for a source at zs = 3 and θE = 27 .″ 9 ± 2 .″ 8 for a source at zs = 9. The total projected mass within a 200 kpc radius around the strong-lensing region is M (&lt;200 kpc) = (1.9 ± 0.3) × 1014 M⊙. While our results rely on photometric redshifts warranting spectroscopic follow-up, this central mass resembles that of the Hubble Frontier Fields clusters—although SPT-CL J0546-5345 is observed when the Universe was ∼3─4 Gyr younger. Amongst the multiply imaged sources, we identify a hyperbolic-umbilic-like configuration, and, thanks to its point-like morphology, a possible active galactic nucleus (AGN). If confirmed spectroscopically, it will add to just a handful of other quasars and AGN known to be multiply lensed by galaxy clusters.

Keywords: Galaxy clusters, High-redshift galaxy clusters, Strong gravitational lensing, Gravitational lensing, Active galactic nuclei
Toward Accurate Asteroseismic Masses for Luminous Giants. Asteroseismology, the study of stellar oscillations, provides high-precision measurements of masses and ages for red giants. Scaling relations are a powerful tool for measuring fundamental stellar parameters, and the derived radii are in good agreement with fundamental data for low-luminosity giants. However, for luminous red giant branch (RGB) stars, there are clear systematic offsets. In APOKASC-3, the third joint spectroscopic and asteroseismic catalog for evolved stars in the Kepler fields, we tied asteroseismic radii to a reference system based on Gaia astrometry by introducing correction factors. This work proposes an alternative formulation of the correction scheme, which substantially reduces the sensitivity of the results to the technique used to infer mean density from frequency spacings. Compared to APOKASC-3, our adjusted correction scheme also reduces fractional discrepancies in median masses and ages of lower RGB and upper RGB within the α-rich population from 6.65% to 1.72% and from −21.81% to −9.55%, respectively. For the α-poor population, the corrected mass scale leads to an improved agreement between theory and observation of the surface carbon-to-nitrogen abundance ratio, a significant diagnostic of the first dredge-up.

Keywords: Asteroseismology, Red giant stars, Stellar masses
Spectral Characteristics of Interstellar Object 3I/ATLAS from SOAR Observations. Interstellar objects (ISOs) provide unique insights into the building blocks and conditions of extrasolar planetary systems. The newly discovered object, 3I/ATLAS (C/2025 N1), represents the third known ISO after 1I/'Oumuamua and 2I/Borisov. We present initial spectroscopic characterizations of 3I using observations from the Goodman High Throughput Spectrograph on the 4.1 m SOAR Telescope in Chile during the night of July 3. The reflectance spectrum of 3I, covering 3700–7000 Å, reveals a red continuum, comparable to extreme trans-Neptunian objects, with a weak UV-optical turnover indicative of complex carbonaceous and irradiated organics. At the time of observation, when 3I was at a heliocentric distance of 4.4 au, we detected no discernible gas emission from canonical cometary species (CN, C3, C2, CO+, and [O I]). This is in agreement with expectations from our thermal evolution model, which indicates sublimation-driven activity should commence once 3I/ATLAS approaches smaller heliocentric distances. Nonetheless, the paradoxical situation of early onset coma without evidence of sublimation tracers calls for other dust-liberating mechanisms that ancient ISOs may be subjected to at large heliocentric distances. *Based on observations collected with the Goodman High Throughput Spectrograph on the 4 m SOAR Telescope at Cerro Pachón Observatory in Chile, under the program allocated by the Chilean Telescope Allocation Committee (CNTAC), program ID CN2025A-96.

Keywords: Comet surfaces, Comet origins, Interstellar objects
The Day-long, Repeating GRB 250702B: A Unique Extragalactic Transient. γ-ray bursts (GRBs) are singular outbursts of high-energy radiation with durations typically lasting from milliseconds to minutes and, in extreme cases, a few hours. They are attributed to the catastrophic outcomes of stellar-scale events and, as such, are not expected to recur. Here, we present observations of the exceptional GRB 250702B (formerly GRB 250702BDE) which triggered the Fermi GRB monitor on three occasions over several hours, and which was detected in soft X-rays by the Einstein Probe several hours before the γ-ray triggers (EP 250702a). We present the discovery of an extremely red infrared counterpart of the event with the Very Large Telescope, as well as radio observations from MeerKAT. Hubble Space Telescope observations pinpoint the source to a nonnuclear location in a host galaxy with complex morphology, implying GRB 250702B is an extragalactic event. The multiwavelength counterpart is well described with standard afterglow models at a relatively low redshift z ∼ 0.3, but the prompt emission does not readily fit within the expectations for either collapsar or merger-driven GRBs. Indeed, a striking feature of the multiple prompt outbursts is that the third occurs at an integer multiple of the interval between the first two. Although not conclusive, this could be indicative of periodicity in the progenitor system. We discuss several possible scenarios to explain the exceptional properties of the burst, which suggest that either a very unusual collapsar or the tidal disruption of a white dwarf by an intermediate-mass black hole are plausible explanations for this unprecedented GRB.

Keywords: Gamma-ray bursts, Core-collapse supernovae, Tidal disruption, X-ray transient sources, Supernovae
EP241021a: A Months-duration X-Ray Transient with Luminous Optical and Radio Emission. We present the discovery of a peculiar X-ray transient, EP241021a, by the Einstein Probe (EP) mission and the results from multiwavelength follow-up observations. The transient was first detected with the Wide-field X-ray Telescope as an intense flare lasting for ∼100 s, reaching a luminosity of L0.5‑4 keV ≈ 1048 erg s‑1. Further observations with EP's Follow-up X-ray Telescope reveal a huge drop in the X-ray flux by a factor of &gt;1000 within 1.5 days. After maintaining a nearly plateau phase for ∼7 days, the X-ray flux decreases ∝t‑1.2 over a period of ∼30 days, followed by a sudden decrease to an undetectable level by EP and XMM-Newton, making it the longest afterglow emission detected among known fast X-ray transients. Bright counterparts at optical and radio wavelengths were also detected, with high peak luminosities in excess of 1044 erg s‑1 and 1041 erg s‑1, respectively. In addition, EP241021a exhibits a nonthermal X-ray spectrum, red optical color, X-ray and optical rebrightenings in the light curves, and fast radio spectral evolution, suggesting that relativistic jets may have been launched. We discuss the possible origins of EP241021a, including a choked jet with supernova shock breakout, a merger-triggered magnetar, a highly structured jet, and a repeating partial tidal disruption event involving an intermediate-mass black hole, but none can perfectly explain the multiwavelength properties. EP241021a may represent a new type of X-ray transient with month-duration evolution timescales; future EP detections and follow-up observations of similar systems will provide statistical samples to understand the underlying mechanisms at work.

Keywords: Gamma-ray bursts, Black holes, Tidal disruption, Relativistic jets, X-ray transient sources
From a Different Star: 3I/ATLAS in the Context of the Ōtautahi–Oxford Interstellar Object Population Model. The discovery of the third interstellar object (ISO), 3I/ATLAS ("3I"), provides a rare chance to directly observe a small body from another solar system. Studying its chemistry and dynamics will add to our understanding of how the processes of planetesimal formation and evolution happen across the Milky Way's disk, and how such objects respond to the Milky Way's potential. In this Letter, we present a first assessment of 3I in the context of the Ōtautahi–Oxford model, which uses data from Gaia in conjunction with models of protoplanetary disk chemistry and Galactic dynamics to predict the properties of the ISO population. The model shows that both the velocity and radiant of 3I are within the expected range. Its velocity predicts an age of over 7.6 Gyr and a high water mass fraction, which may become observable shortly. We also conclude that it is very unlikely that 3I shares an origin with either of the previous two ISO detections.

Keywords: Interstellar objects