Earth and Planetary Astrophysics
Water Production of Interstellar Comet 3I/ATLAS from SOHO/SWAN Observations after Perihelion
M.R.Combi, T. Mâkinen, J.-L. Bertaux et al. (+4 more)
The
Solar Wind ANisotropies (SWAN) all-sky hydrogen Lyman-alpha camera on the
Solar and Heliosphere Observatory (SOHO) observed the hydrogen coma of interstellar comet 3I/ATLAS, also called C/2025 N1 (ATLAS), beginning on November 6, 2025, 9 days after perihelion. Water production rates were calculated from each image of 3I/ATLAS using the methodology of Makinen & Combi (2005, Icarus 177, 217) and fluorescence rates, g-factors, calculated using the daily
solar Lyman-alpha fluxes from the LASP database (https://lasp.colorado.edu/lisird/data) corrected for
solar rotation and for the comet heliocentric velocity. The method has been used for over 90 comet apparitions (Combi 2022; Combi et al. 2019). A water production rate of 3.17 x 10^29 s^-1 was found on November 6 when the comet was at a heliocentric distance of 1.40 au and at a sufficient
solar elongation angle. It decreased over time after that, down to 1-2 x 10^28 s^-1 around 40 days post-perihelion (December 9).
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All authors M.R.Combi, T. Mâkinen, J.-L. Bertaux, E. Quemerais, S. Ferron, R. Lallement, W. Schmidt
Solar and Stellar Astrophysics
On the origin of sinusoidal brightness variations in F to O-type stars through radial velocities
E. Šipková, M. Skarka, M. Vaňko et al. (+3 more)
Stellar variability may originate from various phenomena such as binarity, pulsations, or rotation. These mechanisms can induce flux variations of similar magnitudes, shapes, and periods. We aim to determine mechanisms responsible for the sinusoidal variations in main-sequence
stars hotter than 6500 K. We conducted our analysis using TESS long-cadence data complemented with high-resolution spectra from three spectrographs. From the initial sample of almost 46000 objects, we selected 35 targets for spectroscopic follow-up. Comparison of light curves and radial velocity curves allowed for robust classification of these targets. Among the 35 selected objects, 18 displayed variability, suggesting the presence of a companion (including the discovery of 7 new binary systems and 1 candidate for a triple-
star system), 1 was identified as a new pulsator, 9 as new candidates for spotted
stars, and 7 objects had uncertain classification. Our analysis shows that at least half of randomly selected
stars with sinusoidal brightness variations are binaries. The presented results illustrate the need for an individual approach to
stellar classification, especially in cases where the photometric data alone is insufficient for determining the underlying phenomena behind the observed variations.
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All authors E. Šipková, M. Skarka, M. Vaňko, V. Chmelař, T. Pribulla, Z. Mikulášek
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Gravitational waves from seesaw assisted collapsing domain walls
Debasish Borah and Indrajit Saha
Spontaneous breaking of discrete
symmetries like $Z_2$ leads to the formation of stable topological defects such as domain walls which, if allowed to dominate, can potentially be in conflict with cosmological observations. Incorporating explicit $Z_2$-breaking bias terms can lead to annihilation of such walls while also emitting
stochastic gravitational waves (GW). We study the role of heavy right-handed
neutrinos present in the type-I seesaw framework to generate such a bias term via
quantum corrections. This offers interesting correlations among the seesaw scale, GW peak amplitude and peak frequency which can be probed at present and future experiments related to GW as well as precision measurements of the
cosmic microwave background (CMB). In
flavor symmetric UV complete scenarios with degenerate RHNs at leading order, such tiny coupling of RHNs to a $Z_2$-odd scalar can also lead to small mass splittings suitable for explaining the observed
baryon asymmetry of the universe via resonant leptogenesis.
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High Energy Astrophysical Phenomena
High-energy Neutrino Predictions for T Coronae Borealis: Probing Particle Acceleration in Novae
Prantik Sarmah, Sovan Chakraborty and Xilu Wang
The MAGIC detection of near-TeV gamma rays from the 2021 RS Oph ($2.45$ kpc) outburst has established recurrent novae as TeV particle accelerators. However, the origin of this emission (hadronic vs leptonic) remains unclear due to the lack of coincident
neutrinos detected by IceCube. The upcoming outburst of the much closer T Coronae Borealis (T CrB, $\sim0.887$ kpc) offers a unique opportunity to detect these rare nova
neutrinos. Here we present the first comparative analysis of the hadronic secondary fluxes expected from the upcoming T CrB outburst and evaluate their detectability across major observatories, considering two
proton-acceleration mechanisms: (i) an external shock (ES) at $\sim10^{13}$ cm, and (ii)
magnetic reconnection (MR), near the white
dwarf surface at $\sim10^{9}$ cm. While the
benchmark ES model predicts a gamma-ray flux detectable by current facilities, its corresponding
neutrino flux largely remains undetectable. In contrast, the MR scenario generates a robust
neutrino flux within the reach of IceCube and KM3NeT. Importantly, as the MR-produced gamma-rays are absorbed, the escaping MR
neutrinos will arrive hours before any ES-origin signals. This distinct temporal separation can create a powerful phenomenological signature to disentangle the nova acceleration physics.
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High Energy Astrophysical Phenomena
Esha Kundu
Supernovae (SNe), the catastrophic end of
stars' lives, are among the most energetic phenomena in the universe. Mapping the aftermath of the explosions to the properties of pre-SN
stars is challenging due to the lack of knowledge about the
evolution of different types of
stars. The immediate surroundings of pre-SN
stars carry the signature of the progenitors, and
radio observations are the best way to examine the ambient media. Since
radio emission originates from the interaction of supersonic SN ejecta with the relatively stationary circumstellar medium, with a few years of
radio study, the mass-loss history of progenitor
stars can be probed from just before the explosion of the
star to thousands of years before the onset of the SN. Moreover, this can provide crucial details about the explosions, which are poorly understood to date. In this paper, we review the
radio properties of different types of core-collapse explosions and thermonuclear runaways to understand their mass-loss
evolution–which allows us to unravel the imprints of the progenitors on the surrounding media and thus the nature of the exploded
stars. Additionally, we discuss the current state of the art in this field, including existing and the next-generation
radio facilities with enhanced capabilities that provide further details about these explosions.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Mass-to-Horizon Entropic Cosmology: A Unified Thermodynamic Pathway to Cosmic Acceleration
Tomasz Denkiewicz and Hussain Gohar
We investigate the observational tests of generalized mass-to-horizon entropic cosmology by incorporating large-scale structure growth data in addition to purely
geometric probes. The theoretical framework is constructed from a generalized mass-to-horizon scaling relation, $M \propto L^n$, which implies a corresponding generalized entropic functional $S_n \propto L^{n+1}$. Within this setting,
cosmic acceleration arises as an emergent phenomenon driven by an entropic force acting on the cosmological horizon. While earlier studies demonstrated that these entropic cosmologies can reproduce the background expansion history of the standard $\Lambda$CDM model, here we present a comprehensive observational analysis that jointly employs Pantheon+ Type Ia
supernova data with SH0ES calibration, DESI DR2
baryon acoustic oscillation measurements,
cosmic microwave background (CMB) distance priors, and a suite of cosmological structure growth observations. A
Bayesian model comparison indicates that the entropic models are statistically preferred over the conventional $\Lambda$CDM scenario, thereby providing strong support for an entropic origin of the observed late-time
cosmic acceleration in place of a fundamental cosmological constant.
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Cosmology and Nongalactic Astrophysics
Searching for Cosmological Collider in the Planck CMB Data II: collider templates and Modal analysis
Petar Suman, Dong-Gang Wang, Wuhyun Sohn et al. (+2 more)
Signatures of massive particles during inflation are highly informative targets for cosmological experiments. With recent progress on both theoretical and observational frontiers, we have reached the point where these novel signals of
primordial non-Gaussianities (PNG) can be systematically tested with increasingly precise data. In this paper, we present the results of improved CMB data analysis for cosmological
collider signals using Planck CMB data. To set the stage, we first construct a set of simplified but characteristic
collider templates which are accurate over a broad range of particle masses,
spins and sound speeds. In order to break degeneracies with single-field PNG, we propose an orthogonalization scheme such that the
collider templates are uncorrelated with the highly constrained equilateral and orthogonal shapes. On this basis, we deploy the Modal bispectrum
estimator for the Planck analysis and perform a systematic scan of parameters to search for the most significant
collider signal. The maximum signal-to-noise ratio is found to be $2.35\sigma$ for an orthogonalized massive
spin-0 exchange after taking into account the look-elsewhere effect. In addition, we cross-validate the Modal analysis with the CMB-BEST pipeline, which demonstrates the consistency of results across the
benchmark examples of
collider templates. Given the low signal-to-noise ratio regime we find at the current stage of PNG observations, we believe the orthogonalization procedure provides an optimized strategy for future tests of the cosmological
collider signals.
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All authors Petar Suman, Dong-Gang Wang, Wuhyun Sohn, James R. Fergusson, E.P.S. Shellard
Cosmology and Nongalactic Astrophysics
Primordial black holes and smooth coarse-graining in excursion set theory
Daiki Saito and Koki Tokeshi
The excursion-set formalism enables us to infer the mass distribution of collapsed objects, such as
primordial black holes (PBHs), by the
language of
stochastic processes. Within the framework, this article investigates how a smooth coarse-graining procedure affects the resulting PBH mass function. As a demonstrative example, we employ a Gaussian window function, for which the
stochastic noise becomes fully correlated across scales. It is found that these correlated noises result in a mass function of PBHs, whose maximum and its neighbourhood are predominantly determined by the probability that the density contrast exceeds a given threshold at each mass scale. Our results clarify the role of noise correlations induced by smooth coarse-graining and highlight their importance in predicting the abundance of PBHs.
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Solar and Stellar Astrophysics · Cross-listed from physics.flu-dyn
Small-scale turbulent dynamo for low-Prandtl number fluid: comparison of the theory with results of numerical simulations
A.V. Kopyev, A.S. Il'yn, V.A. Sirota et al. (+1 more)
Context: During the last decades, significant progress has been made in both numerical simulations of turbulent dynamo and theoretical understanding of
turbulence. However, there is still lack of quantitative comparison between the simulations and the theory of the dynamo. Results: We study the critical
magnetic Reynolds number ($Rm_c$) and the growth rate near the threshold both in the limit of very high and in the case of moderate Reynolds numbers. We argue that in Kazantsev equation for
magnetic field generation, one should use the quasi-Lagrangian correlator of velocities instead of Eulerian, as usually implied when comparing theory and simulations. The theoretical results obtained with this correlator agree well with numerical results. We also propose the explanation of the decrease of $Rm_c$ as a function of Reynolds number ($Re$) at intermediate-high $Re$. It is probably due to Reynolds-dependent intermittency of the velocity structure function: we show that the scaling exponent of this function in the inertial range affects strongly the
magnetic field generation, and it is known to be an increasing function of the Reynolds number. Conclusions: Use of quasi-Lagrangian correlator in the Kazantsev theory gives good accordance with numerical simulations. An ideal way to compare them should be to find the correlator substituted to the Kazantsev equation and the generation properties in the same simulation. At least one has to use universal parameters independent of the properties of pumping scale. Reynolds-dependent intermittency can explain recently observed decrease of the critical
magnetic Reynolds number at small Prandtl numbers.
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All authors A.V. Kopyev, A.S. Il'yn, V.A. Sirota, K.P. Zybin
High Energy Astrophysical Phenomena
Inferring Eccentricity of Binary Black Holes from Spin-Orbit Misalignment
Vishal Baibhav
Orbital eccentricity remains one of the least accessible parameters in observations of binary black hole (BBH) systems, largely erased by gravitational radiation long before detection. We introduce a new method to recover this lost parameter by using a more accessible and routinely measurable quantity:
spin-orbit misalignment. In isolated binary
evolution, a natal kick from the second
supernova both tilts the orbital plane and injects orbital eccentricity, forging a direct and quantifiable connection between
spin-tilt and post-
supernova eccentricity. By measuring this
spin-tilt using gravitational waves, we can not only constrain the natal kick, but we can also reconstruct the binary's formation eccentricity. We apply this method to GW190412 and GW241011, assuming an isolated formation channel, and show how their eccentricity at formation can be constrained even in the absence of direct eccentricity measurements. As more advanced detectors come online, improved signal-to-noise ratios will tighten
spin-tilt constraints, allowing more precise and reliable estimates of BBH formation eccentricity. Combining this method with multiband observations from LISA and next-generation (XG) detectors will allow us to recover not only eccentricity but also the binary's orbital separation and
redshift at formation, offering a clearer picture of the birth environments of BBH systems and processes that drive their merger.
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High Energy Astrophysical Phenomena
Multiband optical variability on diverse timescales of the blazar Ton 599 from 2011 to 2023
O. Vince, C. M. Raiteri, M. Villata et al. (+72 more)
(Shortened)Context: We analyze the optical variability of the FSRQ Ton 599 using BVRI photometry from the WEBT collaboration (2011-2023), complemented by photometric and spectroscopic data from the Steward Observatory.\\ Aims: To characterize short- and long-term optical variability – including flux distributions, intranight changes, color
evolution, and spectra – to constrain physical parameters and processes in the central engine.\\ Methods: We tested flux distributions in each filter against normal and log-normal, explored the RMS-flux relation and derived PSDs. We quantified intranight variability using a $\chi^2$ test and fractional variability. From variability timescales, we estimated the emitting region size and
magnetic field. Long-term variability was studied by segmenting the light curve into 12 intervals and analyzing flux statistics. For multi-filter
flares, we computed spectral slopes,
redshift-corrected fluxes, monochromatic luminosities and generated Color-magnitude and color-time diagrams. From low-flux spectra, we measured Mg II line and estimated the black hole mass.\\ Results: Ton 599 showed strong optical variability. Log-normal distributions fit the fluxes better, and all bands show a positive RMS-flux relation with red-noise PSDs.Intranight variability is detected, and used in constraining the emission region and
magnetic field.The R band reaches a peak flux of 23.5 mJy, corresponding to a monochromatic luminosity of $log({\nu}L{\nu})= 48.48 [erg/s]$. We found a redder-when-brighter trend at low fluxes (thermal), achromatic behavior at intermediate levels (possibly due to jet orientation changes), and a bluer-when-brighter trend at high fluxes (synchrotron). Long-term color changes are modest, short-term are significant, with a negative correlation between the amplitude of color changes and the average flux. The estimated SMBH mass is order of $10^8 M_\odot$.
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All authors O. Vince, C. M. Raiteri, M. Villata, A. C. Gupta, J. Kovačević-Dojčinović, M. Lakićević, L. Č. Popović, P. Kushwaha, D. O. Mirzaqulov, S. A. Ehgamberdiev, D. Carosati, S. G. Jorstad, A. P. Marscher, Z. R. Weaver, J. R. Webb, P. S. Smith, W. P. Chen, A. Tsai, H. C. Lin, G. A. Borman, T. S. Grishina, V. A. Hagen-Thorn, E. N. Kopatskaya, E. G. Larionova, V. M. Larionov, L. V. Larionova, D. A. Morozova, S. S. Savchenko, I. S. Troitskiy, Y. V. Troitskaya, A. A. Vasilyev, A. V. Zhovtan, E. V. Shishkina, O. M. Kurtanidze, M. G. Nikolashvili, S. O. Kurtanidze, R. Ivanidze, J. A. Acosta-Pulido, M. I. Carnerero, G. Damljanović, M. Stojanovic, M. D. Jovanovic, V. V. Vlasyuk, O. I. Spiridonova, A. S. Moskvitin, T. Pursimo, D. Elsässer, M. Feige, L. Kunkel, J. Ledermann, D. Reinhart, A. Scherbantin, K. Schoch, R. Steineke, C. Lorey, I. Agudo, J. Escudero Pedrosa, F. J. Aceituno, G. Bonnoli, V. Casanova, D. Morcuende, A. Sota, V. Bozhilov, A. Valcheva, E. Zaharieva, M. Minev, A. Strigachev, R. Bachev, B. Mihov, L. Slavcheva-Mihova, A. C. Sadun, A. Takey, A. Shokry, M. A. El-Sadek, A. Marchiniand G. Verna
Solar and Stellar Astrophysics
Cosmic-Ray-Constrained LSTM Model for Geomagnetic Storm Prediction
Zongyuan Ge, Chenwaner Zhang, Wei Zhou et al. (+2 more)
Geomagnetic storms (GSTs) driven by
solar wind-magnetosphere coupling can severely disrupt technological systems, motivating the need for improved prediction accuracy and longer warning times. In this study, we develop a physics-informed Long Short-Term
Memory (LSTM) model that incorporates
cosmic-ray flux modulation as an additional precursor signal. As coronal mass ejection (CME)-driven disturbances propagate through the heliosphere, enhanced
turbulence and
magnetic-field compression reduce
galactic cosmic-ray (GCR) flux measured by ground-based
neutron monitors (Forbush decreases), providing early information that can precede near-Earth
solar-wind signatures by 1–3 days. We integrate multi-source space-weather data, spanning 1995-2020, including
cosmic-ray observations,
solar wind
plasma parameters, interplanetary
magnetic-field data, and geomagnetic indices. Based on these data, we construct a 19-dimensional feature vector that includes flux background levels, decrease-related indicators, and inter-station correlation measures as model inputs. Employing a 50-unit LSTM architecture, the proposed model achieves root-mean-square errors (RMSE) of 5.106 nT, 8.315 nT, 10.854 nT, 12.883 nT, and 14.788 nT for 2-, 6-, 12-, 24-, and 48-hour predictions, respectively. Incorporating
cosmic-ray information further improves 48-hour forecast skill by up to 25.84% (from 0.178 to 0.224). These results demonstrate the value of physics-informed deep learning and
cosmic-ray precursors for advancing space-weather
forecasting.
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All authors Zongyuan Ge, Chenwaner Zhang, Wei Zhou, Hongyu Zeng, Guiping Zhou
Astrophysics of Galaxies · Cross-listed from gr-qc
Impact of neglecting center-of-mass acceleration in parameter estimation of stellar-mass black holes
Suvikranth Gera and Poulami Dutta Roy
A tertiary body near a coalescing binary can imprint its influence on the gravitational waves (GWs) emitted by that binary in the form of center-of-mass (CoM) acceleration. An example of such a scenario is a binary black hole (BBH) merging near a supermassive black hole, which is touted to occur frequently. The limited low-frequency sensitivity of current GW detectors makes it challenging to detect these effects, as the associated waveform phase remains elusive. However, next-generation (3G) detectors such as
Cosmic Explorer (CE) and Einstein
Telescope (ET), with improved sensitivity at lower frequencies, are expected to be capable of capturing such signatures. In our study, we focus on the
stellar-mass BBHs and explore the parameter space where the CoM acceleration will play a dominant role affecting parameter inference of the binary. We demonstrate that an unaccounted CoM acceleration of a low-mass binary with a total mass of $5\, \rm{M}_{\odot} $ can lead to significant systematic biases, exceeding statistical errors in the estimation of the chirp mass and symmetric mass ratio when the CoM parameter $\alpha$ is as small as $\sim 10^{-9}$ and $10^{-10}$ $\rm{s}^{-1}$ for CE and ET, respectively. We also find that asymmetric binaries are more susceptible to systematic bias when CoM acceleration is neglected. When the effect of CoM acceleration is included in the GW phase, then $\alpha = 10^{-7} \rm s^{-1}$ can be constrained with a bound of $10^{-9} (10^{-11})\, \rm s^{-1}$ for CE (ET). Our study thus highlights the crucial implications of considering the presence of a tertiary body in the GW emitted by a
stellar-mass BBH when observed in 3G detectors.
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Earth and Planetary Astrophysics
From emission to absorption: the FAST observation of the OH 18-cm lines from the Comet C2025/A6
Dongyue Jiang, Lei Qian, Minglei Guo et al. (+14 more)
We observed comet C/2025 A6 with the Five-hundred-meter Aperture Spherical
radio Telescope (FAST) equipped with the ultra-wideband receiver from 2025 October 23 to November 8, and it was the first detection for this comet with FAST.Through trapezoidal fitting of the OH line profiles, we derived the expansion velocities of the water which showed an increase from 1.5$\pm$0.3 km s$^{-1}$ at the heliocentric distance of 0.65 AU to 3.0$\pm$0.9 km s$^{-1}$ at 0.54 AU. Based on these results, we estimated the OH production rates of C/2025 A6 for October 23, October 26, November 4 and November 5 which were (1.0$\pm$0.1)$\times$10$^{29}$, (1.2$\pm$0.1)$\times$10$^{29}$, (1.4$\pm$0.3)$\times$10$^{29}$, and (1.5$\pm$0.4)$\times$10$^{29}$ s$^{-1}$ respectively. The results show a significant upward trend.
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All authors Dongyue Jiang, Lei Qian, Minglei Guo, Qiaoli Hao, Menglin Huang, Peng Jiang, Hongfei Liu, Chun Sun, Xingyi Wang, Qingliang Yang, Naiping Yu, Lei Zhao, Yutao Zhao, Liyun Zhang, Yichi Zhang, Tongjie Zhang, Zhichen Pan
High Energy Astrophysical Phenomena
Superradiant and dynamical spin-down of neutron stars with gravitational wave implications
Indra Kumar Banerjee, Sandeep Chatterjee, Biswarup Das et al. (+1 more)
Neutron stars such as
pulsars and magnetars lose angular momentum primarily through electromagnetic dipole radiation, gravitational waves, $r$-mode oscillation. However,
spin variations, particularly enhanced
spin-down rates, indicate additional
spin-down mechanisms. We propose superradiant
spin-down as a potential faster
spin-down process. By modelling the interplay between conventional and superradiant
spin-down channels, we evaluate their impact on
neutron star rotational
evolution. We also discuss gravitational-wave emission produced by quadrupole deformation, $r$-mode oscillations, and
axion-induced bosonic clouds around an isolated
neutron star, highlighting their potential as distinct multi-messenger probes in upcoming detectors.
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All authors Indra Kumar Banerjee, Sandeep Chatterjee, Biswarup Das, Ujjal Kumar Dey
Instrumentation and Methods for Astrophysics
WST spectroscopic variability alerts: discovery space, data flow system requirements
Valenitn D. Ivanov
The enormous multiplexity of the WST opens up the possibility to trigger alerts for variable objects - an option that has been reserved so far only for imaging surveys. WST can go further by detecting spectroscopic line profile and line strength variations. I review previous alert-issuing surveys that are limited to imaging, and describe some of the new research possibilities that this feature of the data flow system (DFS) would open up. The latter range from variability of emission line
stars, such as Bes, WRs and LBVs to variability of active
galaxies and
quasars, including the so-called changing look objects that shift between Type 1 and Type 2. Furthermore, I describe the requirements that the WST DFS must meet to make this feasible. The most critical aspect is the rapid data processing for timely follow-up. Next, the alert system is tightly connected with the data reduction and archive, because it will need an extensive and continuously updated spectral reference database. The new spectra will have to be compared against these reference spectra to identify variations. The reference spectra can either be "native" from the WST itself or they can originate from other spectroscopic surveys. Two options for the DFS are considered: one is to conduct an automated search of the WST's own archive, and potentially of other spectroscopic archives and a second option is to allow the users to submit reference spectra on their own. The spectroscopic alert system will open up a completely new discovery space that is not accessible to the existing or planned near-future surveys. Finally, I discuss the advantages of moving the variability detection to physical parameters by modeling the observed and reference spectra and comparing the derived fitting parameters. This strategy offers a robust method for alert ranking.
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Astrophysics of Galaxies
A large, long-lived, slowly-expanding superbubble across the Perseus Arm
Bingqiu Chen, Guangxing Li, Haibo Yuan et al. (+5 more)
Stellar feedback is a crucial mechanism in
galactic evolution, as demonstrated by the widespread bubbles observed with JWST. In this study, we combine data from
Gaia and LAMOST to obtain a sample of young O-B2
stars with full three-dimensional velocity information. Focusing on the largest known superbubble in the Milky Way, we identify groups of O-B2
stars at its periphery, exhibiting a transverse velocity of 25.8 km/s and an expansion velocity of 6.2 km/s. Using these velocities, we calculate a crossing time t_cross ~ 20 Myr and an expansion timescale t_expansion ~ 80 Myr. We estimate a survival timescale t_survival ~ 250 Myr and a
supernova interval t_SN ~ 0.1 Myr. Together with the
Galactic shear timescale t_shear ~ 30 Myr, these values satisfy t_SN < t_shear < t_survival. The energy and momentum from
supernovae are sufficient to sustain the bubble's growth against ambient pressure. This indicates that repeated
supernovae replenish energy faster than shear and turbulent distort the cavity. Our analysis classifies the
Giant Oval Cavity as a large, quasi-stationary superbubble, similar to the Phantom Bubble observed by JWST, stabilised by the interplay between
stellar feedback and
Galactic disk dynamics.
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All authors Bingqiu Chen, Guangxing Li, Haibo Yuan, Maosheng Xiang, Jixuan Zhou, Pinjian Chen, Martin Krause, Ashley Coombs
Cosmology and Nongalactic Astrophysics
TITAN DR1: An Improved, Validated, and Systematically-Controlled Recalibration of ATLAS Photometry toward Type Ia Supernova Cosmology
Elijah G. Marlin, Yukei S. Murakami, Dillon Brout et al. (+14 more)
ATLAS (Asteroid Terrestrial Last Alert System) is a time-domain survey using four
telescopes, covering the entire sky. It has observed over 10,000 spectroscopically confirmed Type Ia
supernovae (SNe~Ia), with thousands of cosmology-grade light curves (to be released as TITAN DR1). To prepare this massive, low-
redshift dataset for cosmology, we evaluate and cross-calibrate ATLAS forced photometry using tertiary
stars from the DES (Dark Energy Survey) Y6 release. The 5000 deg$^2$ DES footprint overlaps regions both in and out of the PS1 (Pan-STARRS DR1) footprint, allowing tests of the primary calibrator for the ATLAS Refcat2 catalog. Initial offsets are at the $\sim$40 mmag scale. To improve this we determine $\Delta$ zeropoint offsets for two cases: (1) pixel-to-pixel offsets within individual CCDs (reduced from $\sim$8 to $\sim$4 mmag RMS) and (2) chip-to-chip offsets across the 9 CCDs and filters (reduced from $\sim$17 to $\sim$3 mmag RMS). We also identify the largest systematic uncertainty as a transmission-function color dependence, requiring shifts in the assumed ATLAS filters at the $\sim$30 mmag level if uncorrected. We validate our calibration using (a) CALSPEC standards, (b) an independent tertiary catalog, and (c) distance
moduli of cross-matched SNe~Ia, all showing improved consistency. Overall, we estimate combined calibration-related systematics at the $\sim$5–10 mmag level, supporting competitive cosmological constraints with the TITAN SN~Ia
dataset.
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All authors Elijah G. Marlin, Yukei S. Murakami, Dillon Brout, Jack W. Tweddle, Brodie Popovic, Ken W. Smith, Stephen J. Smartt, Daniel M. Scolnic, David Jones, Erik R. Peterson, Adam G. Riess, Maria Vincenzi, Nora F. Sherman, Maria Acevedo, Jasper Milstein, Mitchell Dixon, Armin Rest
High Energy Astrophysical Phenomena
The First X-ray Polarimetry of GRS 1739–278 Reveals Its Rapidly Spinning Black Hole
Qing-Chang Zhao, Michal Dovciak, Han-Cheng Li et al. (+6 more)
We present a joint spectro-polarimetric analysis of the black hole X-ray binary GRS~1739–278 during its 2025 mini-outburst, using simultaneous observations from \ixpe\ and \nustar. The \ixpe\ data show a polarization degree of ${\rm PD} = (2.3 \pm 0.4)\%$ and a polarization angle of ${\rm PA} = 62^\circ \pm 5^\circ$ in the 2–8~keV range. The model-independent analysis reveals that the PD increases from $\sim 2\%$ at 2~keV to $\sim 10\%$ in the 6–8~keV band, while the PA remains stable across the \ixpe\ band within statistical uncertainties. Broadband spectral modeling of the combined \ixpe\ and \nustar\
datasets shows that hard Comptonization contributes negligibly in this soft-state observation, while a substantial reflected component is required in addition to the thermal disk emission. We then model the \ixpe\ Stokes spectra using the kynbbrr model. The best-fitting results indicate that high-
spin configurations enhance the contribution of reflected returning radiation, which dominates the observed polarization properties. From the kynbbrr modeling, we infer an extreme black hole
spin of $a = 0.994^{+0.004}_{-0.003}$ and a system inclination of $i = 54^\circ{}^{+8^\circ}_{-4^\circ}$. Owing to the large contribution from returning radiation, the observed polarization direction is nearly parallel to the projected system axis, the position angle of which is predicted to be $58^\circ \pm 4^\circ$. Our results demonstrate that X-ray polarimetry, combined with broadband spectroscopy, directly probes the geometry and relativistic effects in
accretion disks around
stellar-mass black holes.
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All authors Qing-Chang Zhao, Michal Dovciak, Han-Cheng Li, Lian Tao, Hua Feng, Federico Vincentelli, Giorgio Matt, Philip Kaaret, Shuang-Nan Zhang
High Energy Astrophysical Phenomena
Component-dependent Periodic Emission Variations of PSR J1857+0943 Observed with FAST
Shi-jun Dang, Ji-guang Lu, Peng Jiang et al. (+12 more)
Single-pulse studies of millisecond
pulsars provide an important way to probe the
plasma processes responsible for their
radio emission, but such studies remain rare because of the weak emission and short rotation periods of these objects. Using the high sensitivity of the Five-hundred-meter Aperture Spherical
radio Telescope (FAST), we investigate the pulse-to-pulse variability of PSR J1857+0943 and report the first detection of distinct fluctuation behavior across its main pulse and interpulse. The integrated main pulse and interpulse each show multiple emission components with markedly different variability properties. Pulse longitude resolved fluctuation analysis reveals quasi-periodic intensity modulation in both pulse regions, with the interpulse showing a characteristic modulation timescale approximately twice that observed in the trailing part of the main pulse. A longitude-resolved cross-correlation analysis further reveals a weak anti-correlation between the trailing main-pulse emission and the interpulse at a lag of one rotation period, suggesting that these widely separated pulse-longitude ranges may be influenced by a common magnetospheric process. The polarization properties of the single pulses in the same longitude range also differ from those of the adjacent main-pulse components, supporting the presence of component-dependent emission behavior. In addition, we measure a one-hour jitter noise of $\sigma_{\rm J,1h}=73.2\pm1.5$ ns at 1.25 GHz, consistent with previous measurements. These results demonstrate that PSR J1857+0943 exhibits complex single-pulse variability and provide new observational constraints on the magnetospheric structure of interpulse millisecond
pulsars.
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All authors Shi-jun Dang, Ji-guang Lu, Peng Jiang, Yu-lan Liu, Jin-tao Xie, Habtamu Menberu Tedila, Fei-fei Kou, Jian-ping Yuan, Zhi-gang Wen, Shuang-qiang Wang, Lun-hua Shang, Zu-rong Zhou, Wen-ming Yan, Qi-jun Zhi, Na Wang
High Energy Astrophysical Phenomena
Long-term monitoring of repeating FRB 20220912A with the uGMRT at low radio frequencies
Ajay Kumar, Yogesh Maan, Banshi Lal et al. (+4 more)
Some repeating FRBs exhibit occasional extreme repetition rates, but very few show a sustained high activity level. One such hyperactive repeater is FRB 20220912A, which was discovered by CHIME/FRB Collaboration on 2022 September 12. Here, we present results from a long-term monitoring campaign of FRB 20220912A using the upgraded
Giant Metrewave
Radio Telescope (uGMRT) in the frequency range from 300 to 750 MHz. Over the course of nearly two years, we detected a total of 643 bursts in this frequency range. The source exhibited extreme activity for a few months after its discovery and sustained its active phase for more than 1.5 years, with unsystematic modulations in the activity during this phase. The cumulative energy distributions in both bands show a break, consistent with other active repeaters like FRB 20121102A, FRB 202011124A, etc., suggesting common underlying emission mechanisms. Moreover, we show that the energy distribution shape for FRB 20220912A remains broadly same across a large range of frequencies and over time. Overall, the extended high activity, estimated total energy output, persistent power-law tails in the energy distributions, and the lack of detectable short timescale periodicity favor progenitor models invoking young dynamic magnetars, potentially emitting pulses across large rotation phase ranges.
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All authors Ajay Kumar, Yogesh Maan, Banshi Lal, Yash Bhusare, Shriharsh P. Tendulkar, Visweshwar Ram Marthi, Puja Majee
Cosmology and Nongalactic Astrophysics
Implications of Cosmic Birefringence for Multi-Field ALP Dark Matter
Jialiang Shao, Ippei Obata and Dongdong Zhang
Cosmic birefringence, characterized by the observed rotation of the polarization plane of the
cosmic microwave background (CMB) radiation, serves as a critical probe for testing theories beyond the standard cosmological scenario. As a major component of the universe, dark matter plays a pivotal role in
cosmic evolution, particularly in the formation of large-scale structures. However, its fundamental nature remains elusive.
Axion-like particles (ALPs), as promising dark matter candidates, possess unique advantages in naturally explaining such phenomena. Previous studies on the implications of
cosmic birefringence for these ultralight ALP fields have focused on single-field models with conventional potentials. These models face exclusion due to the washout effect - a suppression of the CMB polarization power spectrum induced by oscillatory dynamics of the scalar field within the mass range of less than $10^{-23}$ eV. To address this limitation, we develop a more general theoretical framework incorporating two ALP fields, providing analytical approximations and numerical calculations. Our findings reveal that the superposition of two ALP fields with distinct masses can relax the constraints imposed by the washout effect and reconcile with observations.
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High Energy Astrophysical Phenomena
Spectral State Switching in Mrk 421: Results from the AstroSat LAXPC/SXT Observations
Sikandar Akbar, Zahir Shah, Ranjeev Misra et al. (+1 more)
We carried a detailed time and flux resolved X-ray spectral analysis of the high-synchrotron-peaked blazar Mrk\,421 using simultaneous LAXPC20 and SXT observations. The 100\,s binned LAXPC20 light curve obtained during 3–8 January 2017 reveals pronounced flux variability. The source exhibits a fractional variability amplitude of $F_{\mathrm{rms}} = 0.210 \pm 0.005$ in the SXT band and $F_{\mathrm{rms}} = 0.316 \pm 0.006$ in the LAXPC20 band. During this interval, the source reached a peak LAXPC20 count rate of 122.94\,counts\,s$^{-1}$, while the peak count rate in the SXT light curve is 26.79\,counts\,s$^{-1}$. This enabled us to carry out flux-resolved spectroscopy by dividing the 100\,s binned LAXPC20 light curve into ten flux states (S1–S10), each spanning a width of 8\,counts\,s$^{-1}$. For each flux state, simultaneous SXT and LAXPC20 spectra were extracted and fitted jointly. We find that the spectra in these states are well described by a synchrotron-convolved broken power-law, which provides a better fit than a log-parabola model. The low-energy particle index (index before the break) is found to cluster around two discrete values across flux states indicating two spectra states in the source. The break energy consistently moves to high energy with increase in flux level in these states. Time-resolved spectroscopy (10-ks segments) confirms that the flux histogram is best modelled as a double lognormal distribution and the index histogram is double normal. Inclusion of two additional long observations spanning 2017-2019 shows the same double-state behaviour on longer timescales. Together, the results indicate that Mrk\,421 routinely occupies two dominant spectral; in a leptonic synchrotron framework this can be explained by Gaussian-like fluctuations in acceleration conditions producing lognormal flux states.
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All authors Sikandar Akbar, Zahir Shah, Ranjeev Misra, Naseer Iqbal
Solar and Stellar Astrophysics
Compact Ca II K Brightenings Precede Solar Flares: A Dunn Solar Telescope Pilot Study
Aman Priyadarshi M. Kumar, Juie Shetye, Sean G. Sellers et al. (+1 more)
We present a uniform analysis of compact Ca II K (3934 Å) brightenings that occur near
flare kernels and assess their value as short-lead indicators of
solar flare onset. Using high-cadence imaging from the Rapid Oscillations in the
Solar Atmosphere (ROSA) instrument at the Dunn
Solar Telescope (DST), we examine eight
flare sequences (seven C-class and one B-class) obtained between 2021 and 2025. Fixed, detector-coordinate regions of interest are used to generate mean-intensity light curves, which are detrended and smoothed to isolate impulsive brightenings. In every event, a compact Ca II K brightening is detected within or adjacent to the flaring region that peaks 10–45 min before the primary kernel and the corresponding rise in GOES 1–8 Å\ flux. The measured temporal offsets scale with the deprojected separation between the brightening and
flare kernels, implying an apparent propagation speed of $\sim$30–35 km s$^{-1}$ that is consistent with chromospheric reconnection. Complementary Spectropolarimeter for Infrared and Optical Regions (SPINOR) spectropolarimetry for one event shows topological reconfiguration from closed to open or extended connectivity, supporting a reconnection-driven origin. These results demonstrate that compact Ca II K brightenings are reproducible, physically meaningful precursors to
flare onset. Their simplicity and cadence make them attractive chromospheric indicators, and future work will evaluate their predictive skill alongside established UV/EUV and
magnetic diagnostics.
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All authors Aman Priyadarshi M. Kumar, Juie Shetye, Sean G. Sellers, Damian J. Christian
Solar and Stellar Astrophysics
Comprehensive study of solar type II radio bursts and the properties of the associated shock waves
K. Bhandari, D. E. Morosan and S. Normo
Type II
radio bursts are
solar radio emissions generated by electrons accelerated by coronal shocks. These bursts are typically found close to expanding coronal mass ejections (CMEs), making them valuable for studying the properties and dynamics of CME-driven shocks in the
solar corona. Here, we aim to determine the regions in the
solar corona where shock waves accelerate electrons and determine their characteristic properties. To do this, we combine
radio observations of type II
solar radio bursts with magneto-hydrodynamic (MHD) simulations of the
solar corona. We analyse ten type II
radio bursts from
Solar Cycle 25 exhibiting emissions. The novelty of this study lies in using
radio imaging data for all type II bursts to examine the positions of the
radio sources. The
radio source positions, combined with a geometrical fitting of the CME shock and the MHD simulations, are used to determine essential shock parameters at the acceleration region, such as the Alfvén Mach number $(M_{\rm A}$ and $\theta_{\rm BN}$. The shock parameters are then combined with the properties of the
radio emission and the associated eruption in a comprehensive study. We found that for all events, the type II bursts are located near or inside coronal streamers. The estimated shock speeds are high, resulting in the formation of super-critical shocks ($3.8~\leq~M_{\rm A}~\leq~7.7$) at the type II locations. In most events, type II bursts are located at oblique shocks rather than near-perpendicular geometries, suggesting that the shock structure is more complex at local scales than the simple spherical shock models usually applied to CME shocks. Our results suggest that CME-streamer interaction regions are necessary for the generation of type II bursts, as they provide ideal
plasma conditions for the formation of super-critical shocks and the subsequent acceleration of electrons.
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