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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 22 April

High Energy Astrophysical Phenomena

A Search for Rotation Measure Flare Candidates in Repeating Fast Radio Bursts

Ye Li

Fast radio bursts (FRBs) are millisecond-duration extragalactic radio transients of unknown origin. Rotation measures (RMs) probe their local magneto-ionic environments and provide important clues to their nature. While RM variability has been observed in several repeating FRBs, it is typically gradual or stochastic. Recently, observations of FRB~20220529 revealed an abrupt RM excursion followed by rapid recovery on week-long timescales, termed an “RM flare”, suggesting a potentially distinct form of RM variability associated with localized magnetized plasma. In this work, we perform a systematic search for RM flare candidates in repeating FRBs with multi-epoch RM measurements. Using a $3\sigma$ significance threshold, we identify two candidates with multiple observational epochs (FRB~20121102A and FRB~20201124A) and two additional single-epoch candidates (FRB~20180916B), in addition to the event in FRB~20220529A. Our results suggest that RM flares, if confirmed, may not be rare among repeating FRBs and point to highly dynamic magnetized environments local to the sources. Future high-cadence polarimetric observations, particularly following the discovery of RM excursions, will be essential for confirming these candidates and constraining their physical origin.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Geodesic Completeness in General Cosmological Scenarios

William H. Kinney

The well-known Borde-Guth-Vilenkin Theorem shows that inflationary spacetimes are generically geodesically past-incomplete, necessitating the existence of a pre-inflationary boundary of some sort, possibly singular. I discuss the generalization of the BGV theorem to spacetimes beyond inflation, including inhomogeneous and cyclic models. As an example, I show that the cyclic model proposed by Ijjas and Steinhardt is geodesically incomplete.
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Solar and Stellar Astrophysics

Machine Learning-Based Characterization of Solar p-Mode Frequency Shifts during Solar Cycle 25

Rekha Jain, Akash Kumar and Sushanta C. Tripathy

The solar interior is probed by the properties of the Sun's acoustic oscillations (p-modes) observed on the solar surface. The frequencies of these p-modes measured in the last three decades show long term variation similar to the 11 year cyclic behaviour exhibited by 10.7 cm radio flux, sunspot numbers and other solar activity indices. It is also now established that the cyclic behavior of some of the solar proxies are connected with geomagnetic activities and have implications for space weather. Hence, in recent years efforts have been made using machine-learning methods to forecast these solar proxies with a view to improve our understanding of space weather. Developing a comparable method for forecasting p-mode frequency shifts is therefore of interest for two reasons. Firstly, it will facilitate future investigations into its potential role in tracing energy drivers from the Sun's interior to the geospace response by improving models of solar interior dynamics to coronal and heliospheric plasma conditions. In other words, it will help establish a more robust and quantitative link between the Sun's interior and its exterior. Secondly, it may provide us with an independent indicator or an early indicator of ascending and descending phase of solar activity which might be useful for space weather forecasting. In this article, we develop and apply the standard time-series analysis and machine-learning based methods to characterise p-mode frequency shifts for the remaining solar cycle 25.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Irreducible Gravitational Wave Background as a Particle Detector

Anish Ghoshal, Angus Spalding and Graham White

Beyond the standard model particles can imprint a temporary early matter-dominated epoch on a stochastic gravitational-wave background. For a freely propagating background whose production has ceased, we show that the resulting feature contains two characteristic frequencies that determine the particle decay rate $\Gamma$ and the abundance-weighted mass $Y_iM$, independently of the microphysical origin of the gravitational-wave source. Using numerical scans, we derive semi-analytic relations between these characteristic frequencies and the BSM particle parameters, and quantify the parameter ranges over which these relations remain valid. For backgrounds that remain actively sourced, the end of early matter domination continues to define a source-independent cosmological frequency scale controlled by $\Gamma$, although the second feature, and hence the inference of $Y_iM$, is source dependent. Once a particle model and production mechanism are specified, the measured combinations can be translated into masses and microscopic couplings. Remarkably, decay lengths targeted by upcoming long-lived-particle searches map directly onto the nanohertz range in which NANOGrav has reported evidence for a stochastic gravitational-wave background.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Primordial Magnetogenesis and Gravitational Waves from ALP-assisted Phase Transition

Pankaj Borah, P. S. Bhupal Dev and Anish Ghoshal

Sufficiently strong first-order phase transitions (FOPTs) in the early Universe can simultaneously produce an observable stochastic gravitational wave background (SGWB) and a large-scale primordial magnetic field (PMF). The recent $3.8\sigma$ evidence for a non-zero intergalactic magnetic field from anisotropic pair-halo searches using Fermi-LAT data further motivates a cosmological origin. We investigate an FOPT-origin of both cosmic signatures, namely, PMF and SGWB, and their correlation, within a minimal axion-like particle (ALP) framework in which a global $U(1)$ symmetry is spontaneously broken through radiative corrections, with the ALP sector coupled to the Standard Model (SM) via a Higgs-portal. We compute the present-day PMF amplitude and coherence length for both maximally helical and non-helical configurations, accounting for inverse cascade effects. For maximally helical configurations, we find peak field strengths up to $B_0 \sim 10^{-9}$ G at coherence length $\lambda_0 \sim 10^{-3}-10^{-1}$ Mpc, consistent with lower bounds on the IGMF inferred from blazar observations by MAGIC, H.E.S.S. and Fermi-LAT. We show that the ALP parameter region consistent with $\gamma$-ray blazar data (assuming maximally helical fields) simultaneously produces stochastic GW signals detectable at future space-based interferometers, such as LISA, etc., over the ALP decay constant range $10^3~\text{GeV} \lesssim f_a \lesssim 10^5~\text{GeV}$. We demonstrate that these correlated constraints can be directly mapped onto effective ALP couplings to SM particles, e.g., photons, gluons, and fermions. This establishes a multi-messenger complementarity between cosmological observables and laboratory/astrophysical ALP searches, with combined constraints preferring relatively heavy ALPs, $m_a \gtrsim 0.1~\text{GeV}$, accessible to next-generation intensity and energy-frontier experiments.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Spontaneous Baryogenesis from Axions on Induced Electroweak Walls

Miguel Vanvlasselaer and Wen Yin

We propose a baryogenesis mechanism in which an electroweak phase boundary is induced by a wall-like configuration of a scalar field, such as a domain wall or a shock wave, coupled to the Higgs field. If the Higgs mass parameter depends on the scalar field value, the wall locally separates the electroweak-symmetric and broken phases, thereby providing an induced electroweak wall. We focus on the case where the scalar field is an axion-like particle coupled to the SU(2) Chern–Simons density. The motion of the wall then generates a local effective chemical potential for B+L, realizing a spontaneous baryogenesis mechanism. In the presence of unsuppressed sphaleron transitions in front of the wall, this biases the plasma and leads to baryon asymmetry generation. We discuss the parametric conditions for the induced wall, cosmological realizations based on domain walls and shock waves, and the associated implications for baryon inhomogeneities and gravitational waves. The axion coupling is predicted to be sufficiently weak to evade current experimental and observational bounds.
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Solar and Stellar Astrophysics

The Be star omicron Cas is indeed the primary of a triple system

Petr Harmanec, Stephenson Yang, Miroslav Slechta et al. (+3 more)

Analysis of radial velocities of two narrow absorption components in the Mg II 4481 A line demonstrated that the secondary of the Be star omicron Cas is indeed a close binary system composed of two B7 stars orbiting each other with a period of 11.6604 days. Orbital solutions and spectral disentangling lead to consistent system properties. The system is extremely important for the research of Be stars since its future interferometric observations with a~high spatial resolution could allow the mass and perhaps even the radius of a Be star to be derived without too many model assumptions, mainly on the dynamical grounds.
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All authors Petr Harmanec, Stephenson Yang, Miroslav Slechta, Erika D. Grundstrom, Jose Ribeiro, Adam Harmanec

High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Interaction between nuclear clusters and superfluid phonons in the neutron-star inner crust

Masayuki Matsuo, Arata Nishiwaki, Toshiyuki Okihashi et al. (+1 more)

The interaction between lattice vibrations of nuclear clusters and superfluid phonons associated with neutron superfluidity plays an important role in the dynamics of the neutron-star inner crust. While this coupling has been discussed mainly within macroscopic approaches such as hydrodynamics and effective field theory, its microscopic origin and the value of the effective coupling constant have remained unclear. In this work, we derive the interaction between nuclear clusters and superfluid phonons starting from a microscopic description of inner-crust matter. Using nuclear density functional theory, we analyze the response of a neutron superfluid around a single nuclear cluster within the quasiparticle random-phase approximation. From this microscopic response, we obtain the interaction between the cluster and the surrounding superfluid. Matching this result to the long-wavelength effective description, we determine the coupling constant in an effective Hamiltonian describing the mixing between lattice and superfluid phonons. The resulting coupling strength is found to be significantly smaller than previous hydrodynamical estimates. This reduction originates from the suppression of the superfluid phonon amplitude inside and around the nuclear cluster. Our results provide a microscopic determination of the coupling parameter governing lattice-superfluid phonon mixing in the neutron-star inner crust.
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All authors Masayuki Matsuo, Arata Nishiwaki, Toshiyuki Okihashi, Masaru Hongo

Astrophysics of Galaxies

Photometric Identification of Unresolved Binary Stars in Nearby Open Star Clusters

Varvara O. Mikhnevich, Anastasiia Plotnikova, Giovanni Carraro et al. (+1 more)

This paper introduces a new method to search for unresolved binary stars in open star clusters. The work aims at improving the approach introduced previously, which employs the (H-W2)-W1 versus W2-(BP-K) photometric diagram. This diagram, in tandem with the Gaia Color Magnitude Diagram (CMD) and using theoretical isochrones as reference sequences, is used to estimate the binary star fraction and the distribution of the component mass ratio $q$ in eight nearby open star clusters, including Pleiades, Alpha Per, and Praesepe, which we investigated in previous studies. In this study, to alleviate the uncertainties associated with the use of theoretical isochrones, we propose an empirical isochrones approach. We show that this is an effective approach to exploring a wider primary-mass interval, in particular for the region of low-mass sources. Box-and-whisker plots are used to present the distribution of the component mass ratio $q$. The mode of distribution turns out to be in the range $0.43-0.83$ and $0.38-0.63$ for Gaia and infrared-visible photometry, respectively. In addition, we update the algorithm to obtain the binary fraction, whose estimate lies in the range $0.16 - 0.36$ and $0.21 - 0.44$, depending on the adopted method, and show that in previous studies the binary fraction was overestimated. We do not find evidence that the variable spatial resolution of the employed catalogs (Gaia, 2MASS, and WISE) affects the precision of the binary fraction estimate.
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All authors Varvara O. Mikhnevich, Anastasiia Plotnikova, Giovanni Carraro, Anton F. Seleznev

Cosmology and Nongalactic Astrophysics

Forecasts of CMB $E$-mode anomalies for AliCPT-1

Jiazheng Dou and Wen Zhao

The standard $\Lambda$CDM model has been highly successful in describing cosmic microwave background (CMB) observations. Nevertheless, a set of large-scale statistical anomalies persists in temperature anisotropies across WMAP and Planck. CMB $E$-mode polarization offers an independent probe of these anomalies, circumventing the look-elsewhere effect inherent in temperature-only analyses. In this paper, we forecast the capability of the Ali CMB Polarization Telescope (AliCPT), a ground-based CMB experiment in the Northern Hemisphere, to detect such anomalies in large-scale $E$-mode polarization. Using 1000 unconstrained simulations processed with the NILC component separation method, we evaluate four anomaly estimators: dipole modulation, lack of large-angle correlations, quadrupole-octopole alignment, and point-parity asymmetry. Our analysis considers two noise levels for AliCPT, the goal configuration of the Simons Observatory (SO) Large Aperture Telescope (LAT) alone, and a joint AliCPT+SO configuration. For dipole modulation, we validate the local variance estimator on modulated simulations with an input amplitude $A_d = 0.07$, and find that the combined AliCPT+SO dataset is likely to detect the injected $E$-mode modulation at a 99% confidence level. Tests of the full suite of anomaly statistics on unconstrained isotropic simulations indicate that AliCPT alone, owing to its limited sky coverage, might introduce systematic biases or enlarged uncertainties, especially for quadrupole-octopole alignment and point-parity asymmetry. The combination with SO largely restores the statistical distributions to those expected in an ideal full-sky scenario, thereby establishing a near-cosmic-variance benchmark for upcoming anomaly investigations.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Time evolution of a Nambu-Goto string coiling around a Kerr black hole

Hirotaka Yoshino and Kousuke Tanaka

The interaction between a Nambu-Goto string and a Kerr black hole gives one of the methods of energy extraction from a rotating black hole. Although the properties of such processes have been well studied for rigidly rotating strings, little is known for non-rigidly rotating strings. In this paper, we study time evolution of a Nambu-Goto string on the equatorial plane of a Kerr spacetime, which sticks on the horizon and extends to spatial infinity. The time evolution is studied by the series expansion with respect to $t$ and the numerical simulations, which give reliable results for $t\lesssim 4M$ and $t\lesssim 38M$, respectively, where $M$ is the black hole mass. Since the angular velocity of the string on the horizon must coincide with the horizon angular velocity to keep the timelike property, the string is dragged into rotation and coils around the black hole. The negative energy is observed to fall into the black hole, but the positive energy follows after that, meaning that the energy extraction occurs for a short period of time. In the outside region, a wave is generated and propagates to the distant region carrying the extracted energy. After the propagation of the wave, the system approaches the time-independent configuration found by Boos and Frolov, and the total extracted energy is estimated as $E_{\rm ext}\lesssim \mu M$, where $\mu$ is the tension of the string.
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Instrumentation and Methods for Astrophysics

A Python/CuPy Software Correlator for QUEST: Real-Time Performance and Initial Imaging

Jialang Ding, Guanhong Lin, Dejia Zhou et al. (+20 more)

We present a Python/CuPy FX software correlator for small radio interferometer arrays and evaluate it on QUEST (Qilu University Explorer Survey Telescope). The system combines multi-threaded data ingest, pinned-memory host-device transfers, GPU-accelerated correlation, Polyphase Filter Bank channelization, MAD-based RFI flagging, and delay/phase calibration in a single workflow aimed at array commissioning. On a single NVIDIA RTX 4090D GPU, the implementation reaches a peak throughput of 1.51 GB/s, which is sufficient for real-time operation in the four-antenna mode tested here. After calibration, the visibility phase across a clean 1.32-1.38 GHz band is flattened to a residual scatter of a few degrees. Using the calibrated visibilities, we form a four-antenna synthesis image of Cassiopeia A; the CLEANed image recovers a compact source at the phase center and reduces image-domain background fluctuations from order 0.1 to a few 0.01 Jy/beam. These results indicate that the software is suitable for small-array commissioning and initial synthesis imaging on QUEST. A GNSS-based beam measurement is included as a supporting commissioning check.
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All authors Jialang Ding, Guanhong Lin, Dejia Zhou, Jianli Zhang, Ran Duan, Fei Liu, Xiaoyun Ma, Jie Zhang, Meng Liu, Chenchen Miao, Yuan Liang, Liaoyuan Liu, Yingrou Zhan, Yuting Chu, Jing Qiao, Wei Wang, Zerui Wang, Menquan Liu, Meng Guo, Di Li, Pei Wang, Xuanyu Wang, Xiaohui Yan

Instrumentation and Methods for Astrophysics

Review: A new method for estimation and use of systematic errors in Poisson regression

M. Bonamente

A new method for including systematic errors in the regression with Poisson data is reviewed in this contribution, with emphasis on applications to astronomical spectra. The method consists of generalizing the usual Poisson log-likelihood, known as the Cash statistic $C_{min}$, and its associated likelihood-ratio statistic $\Delta C$, to include the presence of systematic sources of uncertainty. Advantages of this new method include its modeling simplicity and its ability to assess both the level of systematics and the goodness of fit at the same time, including for a nested model component.
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2604.20632 · 22 Apr · Accepted for Frontiers in Astronomy and Space Sciences - Astrostatistics. This is a review of https://ui.adsabs.harvard.edu/abs/2025ApJ...980..139B and https://ui.adsabs.harvard.edu/abs/2025ApJ...980..140B presented at the sys2025 workshop in Huntsville, AL (Nov 14-17. 2025)

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High Energy Astrophysical Phenomena

Deep VLBI constraints on compact radio cores in four ultraluminous X-ray sources

Ailing Wang, Hua Feng, Tao An et al. (+7 more)

We present high-sensitivity Very Long Baseline Interferometry (VLBI) observations of four ultraluminous X-ray sources (ULXs): Holmberg II X-1, IC 342 X-1, NGC 6946 X-1, and NGC 925 X-1. No compact emission was detected on milliarcsecond scales, with rms noise levels reaching approximately 5–20 $\mu$Jy. The corresponding $5\sigma$ flux density upper limits reach $\sim 26\,\mu\mathrm{Jy}$, implying radio luminosity limits $L_{\rm R} \lesssim 2 \times 10^{33}\,\mathrm{erg\,s^{-1}}$. This disfavors any persistently bright hard-state-like compact core at our sensitivity level. The previously reported VLBI core in Holmberg II X-1 exhibits significant long-term variability, broadly consistent with an overall decline over the past decades. This behavior is consistent with emission from optically-thin ejecta undergoing adiabatic expansion. The VLBI non-detections may reflect intrinsically weak/intermittent compact emission, and/or low–surface–brightness structure that is resolved out by VLBI, and/or absorption/propagation effects such as free–free absorption in dense, ionized winds.
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All authors Ailing Wang, Hua Feng, Tao An, Yijia Zhang, Jun Yang, Roberto Soria, Lian Tao, Thomas Russell, Jing Guo, Liang Zhang

High Energy Astrophysical Phenomena

Approximating General Relativity in Core-Collapse Supernova Simulations

Steven A. Fromm, Vassilios Mewes, O. E. Bronson Messer et al. (+3 more)

We present formulations of effective potentials suitable for approximating general relativistic effects in Newtonian simulations of core-collapse supernovae. Assuming a spherically symmetric spacetime and a stress-energy tensor that includes both fluid and neutrino contributions, Eulerian and Lagrangian projections of the Einstein equations are made to determine general relativistic corrections to the Newtonian gravitational potential. We implement the effective potentials in both the Chimera and Flash-X codes, and perform a series of adiabatic and core collapse simulations. The results are compared to Newtonian and fully general relativistic simulations, as well as another widely used effective potential formulation. We find close agreement between our new effective potentials and the fully general relativistic results from multiple other codes.
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All authors Steven A. Fromm, Vassilios Mewes, O. E. Bronson Messer, Eric J. Lentz, W. Raphael Hix, J. Austin Harris

Solar and Stellar Astrophysics

Polytropic stellar wind models with strongly localized heating

L. Westrich, B. Shergelashvili, H. Fichtner et al. (+1 more)

Polytropic models of stellar winds remain to be useful tools because they allow for a simple description of the energy balance of the expanding plasma without explicitly specifying potentially complex energy transport processes like, e.g., heat conduction or extended wave heating. Among recent applications to stellar winds and to the solar wind was a study of the consequences of strongly localized heating in the latter, possibly due to acoustic waves. Such 'nonuniform' heating can result from a time- and space-localized damping of wave modes and allows, as an extreme case, an adiabatic expansion of particular wind streams outside the heating region. The present study generalizes the modeling from the first analytical as well as numerical studies, that were limited to this extreme case, towards a more realistic non-adiabatic behaviour. The additional energy due to heating is demonstrated to be in a plausible range in view of typical flare energies and low compared to the gravitational energy of the plasma in this region. The corresponding solutions may be of interest for stellar winds, in general, and w.r.t. recent observations made with the Parker Solar Probe, which revealed strongly varying wind streams and the presence of acoustic waves near the Sun, for the solar wind, in particular. Potential observational evidence for the solar wind is discussed.
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All authors L. Westrich, B. Shergelashvili, H. Fichtner, V. N. Melnik

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Reshaping the inner shadow of a Kerr black hole by a torn accretion disk

Shiyang Hu, Dan Li, Chen Deng et al. (+1 more)

When an accretion flow extends to the event horizon, their intersection defines the contour of the inner shadow. However, the morphological evolution of this critical feature remains largely unexplored within a torn accretion disk system, a configuration comprising distinct sub-disks formed when a tilted disk is disrupted by frame-dragging. To address this, we phenomenologically construct a torn accretion disk model and numerically simulate the inner shadow of a Kerr black hole using relativistic backward ray-tracing. We discover that the torn disk geometry profoundly alters the black hole's observational signatures, inducing severe erosion of the inner shadow and generating novel features such as bifurcated shadows, crescent-like structures, and multiple orders of shadow rings. These exotic morphologies, which are predominantly governed by the spatial discontinuity between the sub-disks and the tilt angle of the outer sub-disk, are exceedingly difficult to replicate within standard equatorial accretion paradigms. Our findings demonstrate that these distinctive shadow structures hold significant potential to serve as robust diagnostic probes for torn accretion environments, simultaneously implying that relying solely on the inner shadow to test gravity theories is fundamentally insufficient.
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All authors Shiyang Hu, Dan Li, Chen Deng, Kejian He

High Energy Astrophysical Phenomena

The January 2010 flare of Mrk421: Insights from a stochastic acceleration model

MAGIC collaboration: K. Abe, S. Abe, J. Abhir et al. (+190 more)

Mrk421 displayed its highest flux state ever observed in February of 2010 with very high TeV fluxes and interesting cross-band correlations and a spectral energy distribution (SED) evolution not entirely consistent with the standard single zone leptonic synchrotron self-Compton model. The source was already in a high state in January 2010 and displayed strong variability in the days preceding the highest state. We study the temporal evolution of the spectra in January to extract information about the particle dynamics and the physical properties of the emission region. We build up on the temporal variability and correlations studied in the previous work (MAGIC collaboration - Abe et al. 2025) and attempt to improve the SED model fits with a physics oriented approach. The multi-wavelength data was processed and the SEDs were fit using JetSeT. The SED evolution and cross band correlations were modelled using leptonic log-parabola with a low energy power-law branch (LPPL) and pile-up distributions that are predicted in a stochastic acceleration scenario. A simplified temporal evolution model was developed and fit to the SEDs and the resulting trends and phenomenology were characterised in context of theoretical literature. An expanding emission region model was also tested. We find the spectral variability to be well in agreement with stochastic acceleration. Our analysis suggests that the standard LPPL distribution develops a Maxwellian pile-up component at the transition from acceleration to cooling dominated phase on 3 nights in the dataset, as also hinted by the very-high energy and X-ray light curves. The resulting phenomenology of our sequential snapshot evolution SED model agrees well with theoretical and numerical simulation studies on temporal evolution using the diffusion equation approach.
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All authors MAGIC collaboration: K. Abe, S. Abe, J. Abhir, A. Abhishek, V. A. Acciari, A. Aguasca-Cabot, I. Agudo, I. Albanese, T. Aniello, L. A. Antonelli, A. Arbet-Engels, C. Arcaro, T. T. H. Arnesen, A. Babić, C. Bakshi, U. Barres de Almeida, J. A. Barrio, L. Barrios-Jiménez, I. Batković, J. Baxter, J. Becerra González, W. Bednarek, E. Bernardini, J. Bernete, A. Berti, J. Besenrieder, C. Bigongiari, A. Biland, O. Blanch, G. Bonnoli, Ž. Bošnjak, E. Bronzini, I. Burelli, A. Campoy-Ordaz, A. Carosi, R. Carosi, M. Carretero-Castrillo, D. Cerasole, G. Ceribella, A. Cerviño, Y. Chai, G. Chon, A. Cifuentes Santos, J. L. Contreras, J. Cortina, S. Covino, G. D'Amico, P. Da Vela, F. Dazzi, A. De Angelis, B. De Lotto, R. de Menezes, M. Delfino, J. Delgado, C. Delgado Mendez, F. Di Pierro, R. Di Tria, L. Di Venere, A. Dinesh, D. Dominis Prester, A. Donini, D. Dorner, M. Doro, L. Eisenberger, D. Elsaesser, L. Foffano, L. Font, F. Frías García-Lago, Y. Fukazawa, S. García Soto, S. Gasparyan, M. Gaug, J. G. Giesbrecht Paiva, N. Giglietto, F. Giordano, P. Gliwny, T. Gradetzke, R. Grau, J. G. Green, P. Günther, D. Hadasch, A. Hahn, G. Harutyunyan, T. Hassan, J. Herrera Llorente, D. Hrupec, D. Israyelyan, J. Jahanvi, I. Jiménez Martínez, J. Jiménez Quiles, J. Jormanainen, S. Kankkunen, T. Kayanoki, G. W. Kluge, J. Konrad, P. M. Kouch, H. Kubo, J. Kushida, M. Láinez, A. Lamastra, E. Lindfors, S. Lombardi, F. Longo, R. López-Coto, M. López-Moya, A. López-Oramas, S. Loporchio, L. Lulić, E. Lyard, P. Majumdar, M. Makariev, M. Mallamaci, G. Maneva, M. Manganaro, S. Mangano, M. Mariotti, M. Martínez, P. Maruševec, D. Mazin, S. Menchiari, J. Méndez Gallego, S. Menon, D. Miceli, J. M. Miranda, R. Mirzoyan, M. Molero González, E. Molina, H. A. Mondal, A. Moralejo, C. Nanci, A. Negro, V. Neustroev, M. Nievas Rosillo, C. Nigro, L. Nikolić, K. Nilsson, S. Nozaki, A. Okumura, J. Otero-Santos, S. Paiano, D. Paneque, R. Paoletti, J. M. Paredes, M. Peresano, M. Persic, M. Pihet, G. Pirola, F. Podobnik, P. G. Prada Moroni, E. Prandini, W. Rhode, M. Ribó, J. Rico, A. Roy, N. Sahakyan, F. G. Saturni, F. Schiavone, K. Schmitz, F. Schmuckermaier, A. Sciaccaluga, G. Silvestri, A. Simongini, J. Sitarek, V. Sliusar, D. Sobczynska, A. Stamerra, J. Strišković, D. Strom, Y. Suda, M. Takahashi, R. Takeishi, J. Tartera Barberà, P. Temnikov, T. Terzić, M. Teshima, A. Tutone, S. Ubach, M. Vazquez Acosta, S. Ventura, G. Verna, I. Viale, A. Vigliano, C. F. Vigorito, E. Visentin, V. Vitale, M. Vorbrugg, I. Vovk, R. Walter, C. Walther, F. Wersig, P. K. H. Yeung, M. Perri, A. Tramacere

Solar and Stellar Astrophysics

Mid-infrared JWST spectra of carbon stars in the Large Magellanic Cloud

G. C. Sloan, B. Aringer, Kathleen E. Kraemer et al. (+11 more)

Mid-infrared spectra from the Medium Resolution Spectrometer on the James Webb Space Telescope have revealed the molecular chemistry of carbon stars in the Large Magellanic Cloud with better resolution and sensitivity than previously possible. Our sample spans a range of dust-production rates and includes three relatively dust-free semiregular variables and six dustier Mira variables. All were observed 15-20 yr earlier with the Infrared Spectrograph on the Spitzer Space Telescope at lower spectral resolution. The new spectra show that the C3 molecule is responsible for a strong absorption band centered at 5.2 um. CS is clearly present in some of the sample, especially the stars with less dust. HCN also appears to be present. Some of the spectra have changed significantly between the Spitzer epoch and the MRS observations in 2023 and 2024, and in most cases these changes can be attributed to the stellar pulsation cycle. One exception is the disappearance of a dust emission feature at ~18 um in one of the Miras. The new spectra reveal a dip centered at ~10 um, which could arise either from an unknown carrier or from variable molecular emission to the red and blue. The presence of this spectral structure on the short-wavelength side of the SiC dust emission feature at ~11.3 um along with the broad C2H2 band centered at 14 um raise the possibility that some previously reported detections of weak SiC dust emission in other carbon stars may not be real.
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All authors G. C. Sloan, B. Aringer, Kathleen E. Kraemer, J. Cami, K. Eriksson, S. Hoefner, K. Justtanont, E. Lagadec, Paola Marigo, M. Matsuura, I. McDonald, E. J. Montiel, R. Sahai, A. A. Zijlstra

Astrophysics of Galaxies

The Evolution of the SFR-M_* relation at 0.1<z<4: Environmental and Morphological Dependencies

Kaimin He, Ke Shi, Jun Toshikawa et al. (+2 more)

We present a comprehensive study of the relationship between star formation rate (SFR) and stellar mass (M_*) from z = 0.1 to z = 4 using a mass-complete sample of approximately 290,000 galaxies from the COSMOS2020 catalog. We find that the SFR-M_* relation exhibits a pronounced high-mass decline that becomes increasingly evident at lower redshifts. Examining environmental and morphological dependencies, we find strikingly different patterns. For all galaxies, we find galaxies in high-density environments exhibit suppressed star formation rates at z < 1 especially at high-mass end, while for star-forming galaxies no apparent environmental effect is found at all redshifts. In contrast, galaxy morphology exerts strong influence on the SFR-M_* relation at z < 2, in a sense that early-type galaxies exhibit systematically lower star formation rates at fixed mass compared to spirals and irregulars, with this trend persisting even within the star-forming population. These results suggest that internal structural properties (bulge components in particular) continuously regulate star formation efficiency independently of whether galaxies are classified as active or quiescent, whereas external environmental processes primarily serve as rapid quenching mechanisms that increase the fraction of quiescent galaxies at low redshifts. We attribute the observed high-mass decline of the SFR-M_* relation to COSMOS2020's superior capability for detecting massive star-forming galaxies undergoing "morphological quenching" processes.
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All authors Kaimin He, Ke Shi, Jun Toshikawa, Xianzhong Zheng, Xiaopeng You

Solar and Stellar Astrophysics

Formation of classical Be-stars of the early spectral subclass in the case of nonconservative mass transfer in close binary systems

Evgeny Staritsin

Spin-up of a mass gaining component in a binary system is considered taking into account the mass loss from the system during the mass transfer between components in the Hertzsprung gap. The angular momentum that the accreting component gains during mass transfer depends on the increase in the mass of the component at this stage. The increase in the mass was considered over a broad range, from 5% to 100%. The case is considered when, after mass transfer, the mass of the accreting component has a value of 16 M_solar, typical for early Be stars. The transfer of angular momentum within the accreting component occurs due to meridional circulation and shear turbulence. If the accreted mass accounts for more than 30%, the accretor obtains a rotation typical of early Be-stars. This conclusion does not depend on: a) the rotation of the accreting component before mass transfer, b) the amount of angular momentum coming from the boundary layer located between the star and the accretion disk, c) a possible decrease in the angular velocity of the disk below the Keplerian value, d) the efficiency of turbulence in the interior of the accretor.
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High Energy Astrophysical Phenomena

XRF 241001A/SN 2024aiiq: A faint soft X-ray transient detected by SVOM with a broad-line type Ic supernova revealed by JWST

B. Schneider, M. Brunet, B. P. Gompertz et al. (+61 more)

X-ray flashes (XRFs) are a type of gamma-ray burst (GRB) with prompt emission predominantly below 30 keV and have been poorly detected by previous missions. The advent of the SVOM mission, with its wide-field instrument ECLAIRs, provides a new way to detect soft X-ray transients. We present photometric and spectroscopic observations of XRF 241001A detected by SVOM, a soft, subluminous, and low-energetic burst located in a poorly populated region of the Amati relation. We investigated the origin of its faint, soft high-energy emission to assess its connection to the long GRB population. We analyzed the SVOM/ECLAIRs prompt emission and modeled its afterglow emission from X-ray to-radio. We present JWST/NIRSpec and SVOM/VT observations of the associated supernova (SN 2024aiiq), and we compared its properties with previously detected GRB/SNe. The event XRF 241001A is located at z = 0.573 and has a prompt emission dominated by photons below 20 keV with a duration of T90 = 3.14 seconds. Its spectrum is consistent with both thermal and nonthermal models, each implying a low Epeak < 10 keV and Eiso ~ 8x10^49 erg. The X-ray-to-radio afterglow modeling favors an origin from a relativistic jet viewed on-axis. In the optical, XRF 241001A exhibits an early blue emission, similar to that detected in some eFXTs and inconsistent with synchrotron emission. The JWST/NIRSpec observations firmly established its collapsar origin by revealing a SN Type Ic with broad lines, comparable to SN 1998bw and SN 2025kg-like events. The event XRF 241001A is a soft low-luminosity collapsar event produced by a weak relativistic jet observed on-axis, supporting the view that part of the XRF population forms the low-energy soft tail of the long GRB population. Its observation demonstrates the potential of SVOM/ECLAIRs to probe the soft regime of the high-energy transient population that remains largely unexplored.
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All authors B. Schneider, M. Brunet, B. P. Gompertz, D. Turpin, D. B. Malesani, O. Godet, A. J. Levan, F. Daigne, N. Sarin, N. A. Rakotondrainibe, A. Martin-Carrillo, J. T. Palmerio, C. C. Thöne, H. L. Li, A. Saccardi, A. de Ugarte Postigo, S. Antier, V. Buat, D. Ďurovčíková, L. Izzo, J. K. Leung, G. Mo, Y. L. Qiu, S. D. Vergani, J. Wang, J. Y. Wei, L. P. Xin, R. Mochkovitch, B. Zhang, H. B. Cai, S. Campana, A. Coleiro, B. Cordier, P. D'Avanzo, N. Dagoneau, V. D'Elia, Y. W. Dong, D. Götz, S. Guillot, X. H. Han, D. H. Hartmann, L. Huang, Y. F. Huang, P. Jakobsson, A. Klotz, C. Lachaud, E. Le Floc'h, X. M. Lu, P. Maggi, M. De Pasquale, F. Piron, R. Salvaterra, S. Schanne, J. Sollerman, N. R. Tanvir, Z. Vidadi, P. Wang, C. Wu, S. L. Xiong, Y. Xu, T. Zafar, P. P. Zhang, S. N. Zhang, S. J. Zheng

Astrophysics of Galaxies

The core of the problem: Physical limits of the core-Sérsic model

Maarten Baes

The core-Sérsic model is the standard tool for describing partially depleted stellar cores in massive early-type galaxies, yet its physical admissibility has rarely been examined. Using numerical deprojections, we show that many formally allowed parameter combinations cannot represent realistic stellar systems: sharp transitions between the inner power-law core and the outer Sérsic profile (large $\alpha$) always generate non-monotonic intrinsic density profiles. We identify, for each set of structural parameters $(\gamma, m, R_{\text{e}}/R_{\text{b}})$, a critical transition parameter, $\alpha_{\text{crit}}$, above which monotonicity is violated. This threshold systematically depends on the core slope and Sérsic index, implying that a fraction of the commonly used parameter space, including the widely adopted sharp-transition limit $\alpha\rightarrow\infty$, is physically ruled out. These constraints have important consequences for measuring core sizes and mass deficits in massive ellipticals, for constructing dynamical models, and for comparing observations with simulations of supermassive black hole binary evolution.
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Earth and Planetary Astrophysics

Stellar flare-driven evolution of primordial early exo-Earth atmospheres: Insights from a Young M Dwarf Flare model

E. Mamonova, K. Herbst, V. Kofman et al. (+4 more)

Context. M dwarfs are key targets for terrestrial exoplanet studies, with prospects for atmospheric spectroscopy. However, strong stellar magnetic activity and frequent flaring require modelling efforts to assess their impact on planetary atmospheres. Aims. We aim to investigate one year of atmospheric chemical evolution of a young exo Earth orbiting an active M dwarf by coupling our Young M Dwarfs Flare (YMDF) model of stellar activity with the VULCAN chemistry kinetic code. Methods. The YMDF model provides time-resolved spectral energy distributions for high- and low-energy electron beam-driven flares, which are used as external radiative inputs to VULCAN to compute the time-dependent photochemistry and kinetics for different primordial atmospheric scenarios. Results. We present the impact of stellar flares on atmospheres with varying water vapour content, ranging from a plausible primordial atmosphere with solar abundances, representative of a planet-forming region in a dissipating protoplanetary disk, to an extreme water-steam atmosphere with minimal other species. This was explored across several configurations: variable flux in the YMDF model, the previous model representing an active but older M dwarf with added 10K or 400K bottom boundary heat flux, and a constant stellar flux model. Conclusions. Our study suggests that, compared to the previous model, the YMDF model produces synthetic flares that exert significantly greater stress on primordial atmospheres, regardless of the water-vapour content. Increased activity and prevalence of mid-size flares have the potential to induce permanent changes in atmospheric mixing ratios, especially in species with low abundances.
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All authors E. Mamonova, K. Herbst, V. Kofman, O. Ozgurel, A. F. Kowalski, S. Wedemeyer, S. C. Werner

Earth and Planetary Astrophysics

Europa's Lyman-$\alpha$ emissions from HST/STIS observations

L. Roth, K.D. Retherford, J. Saur et al. (+13 more)

An image of Lyman-$\alpha$ (Ly$\alpha$) emission from Europa obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph (HST/STIS) has previously provided the first evidence of localized water vapor (H$_2$O) aurora, potentially originating from outgassing. Subsequent STIS observations have revealed the presence of a global atomic hydrogen (H) exosphere. We present a comprehensive analysis of STIS Ly$\alpha$ observations of Europa acquired in 1999 and between 2012 and 2020 to search for localized auroral emissions and constrain the properties of Europa's H exosphere. We analyze the complete dataset of STIS observations obtained when Europa was sunlit and not transiting Jupiter. A forward model is constructed to account for all known sources of Ly$\alpha$ emission, including resonantly scattered sunlight from Europa's H exosphere. To identify localized anomalies, such as H$_2$O aurora, the modeled Ly$\alpha$ emission is subtracted and the residuals are examined. Emission from Europa's H exosphere is detected at all observing epochs, but is attenuated by absorption in Earth's exosphere when Europa's radial velocity relative to Earth (and thus the Doppler shift) is small. From the velocity dependence of this attenuation, we estimate an H-exosphere temperature of $\sim 1000$ K and derive an upper limit of 5100 K. For the best-constrained epoch in 2014–2015, we infer a vertical H column density of $1.4x10^{12}$ cm$^{-2}$ and an H source rate of $1.1x10^{27}$ s$^{-1}$. No localized emission enhancements are detected in any of the observations, including the image previously interpreted as evidence of H$_2$O aurora near Europa's south pole. The discrepancy with earlier results arises primarily from differences in the assumed position of Europa's disk on the detector, as well as from the inclusion of an H-exosphere signal in the present analysis...
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All authors L. Roth, K.D. Retherford, J. Saur, D.F. Strobel, T. Becker, S. Bergman, A. Blöcker, S.R. Carberry Mogan, C. Grava, M. Ivchenko, S. Joshi, M.A. McGrath, F. Nimmo, L. Paganini, W. Pryor, J.R. Spencer

Solar and Stellar Astrophysics

Shortest period for outer orbit in compact hierarchical triple? Discovery of SB1 around V0885 Per

Mikhail Kovalev

I present a discovery of SB1 in the LAMOST-MRS spectra of eclipsing contact binary V 885 Per. Spectroscopic orbit has period only $P=21.8$ day, which will make it shortest known outer period in compact hierarchical triple system, if this SB1 is indeed bound to the inner system. Unfortunately quality of available spectra don't allow to give definitive answer to this question, with other orbital hierarchy like 2+2 is also possible. Analysis of the eclipse timing variations showed a gradual increase in the orbital period of the inner eclipsing pair, as well as long-term changes that can be explained either by the light time travel effect due to an additional component or by magnetic activity.
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Solar and Stellar Astrophysics

Ancient 'ghost' planetary nebulae discovered with amateur telescopes

J.A. Manuel, D. Jones, M. Santander-García et al. (+1 more)

As planetary nebulae evolve, they fade and dissipate into the surrounding interstellar medium making them harder to detect. Modern, advanced amateur equipment can help to uncover this hidden population of ancient 'ghost' planetary nebulae. Via careful processing of long-integration, narrow-band imagery with modest aperture telescopes at a dark-sky site, we reveal three new candidate planetary nebulae (JAM 2, JAM 3, and JAM 4). Each measures several arcminutes across with [O iii] surface brightnesses of order 30 mag arcsec$^{-2}$. For each nebula, we identify a candidate central star, the parallaxes of which lead to nebular age estimates in the range 50-100 thousand years. The candidate central star of JAM 2 also shows indications of photometric variability, potentially due to spots on the stellar surface.
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All authors J.A. Manuel, D. Jones, M. Santander-García, N. Reindl

Instrumentation and Methods for Astrophysics

Measuring Tianlai's primary beam using sky model

Yunbo Geng, Furen Deng, Jixia Li et al. (+6 more)

We present the beam pattern measurement of the Tianlai Cylinder Pathfinder Array. As it is a pure drift-scan instrument, we exploit the North-South motion of the Sun to demonstrate that the primary beam is factorizable. Leveraging this property, we decompose the primary beam into independent East-West (E-W) and North-South (N-S) components. Using the Sun as a calibration source, we obtain the E-W beam profiles at various elevations, applying normalization to eliminate the effects of solar activity. Subsequently, we simulate the observed signals using a sky map model to derive the best-fit N-S beam. The results of this work are consistent with previous expectations.
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All authors Yunbo Geng, Furen Deng, Jixia Li, Shifan Zuo, Shijie Sun, Yichao Li, Fengquan Wu, Yougang Wang, Xuelei Chen

Solar and Stellar Astrophysics

Solar Energetic Particle Events and Associated Type II Radio Bursts from Different Source Regions

Xuchun Duan, Ting Li, Yingli Cui et al. (+7 more)

Large solar energetic particle (SEP) events are thought to originate from the shocks driven by fast coronal mass ejections (CMEs) and thus generally accompanied by type II radio bursts. However, a significant proportion of type II radio bursts is not accompanied by SEP events. To study the relationship between SEPs and type II radio bursts and the associated physical mechanisms, we statistically analyze 43 SEP halo-CMEs and 131 non-SEP halo-CMEs observed from 2010 to 2024, and check the related properties of type II radio bursts and solar source region. We find nearly all SEP events and approximately two-thirds of non-SEP events are accompanied by type II radio bursts. Type II radio bursts associated with SEP events usually have longer duration and lower ending frequencies. The starting frequency exhibits a clear source region dependence, being highest for ”single active region (AR)”, intermediate for ”multiple ARs”, and lowest for ”outside of ARs”. Furthermore, the spectra of both protons and electrons exhibit a similar softening trend in the three types of source regions. Joint analysis of spectra and type II radio bursts reveals that the proton spectra index has a good anti-correlation with the starting frequency of the type II radio bursts. Our statistical results have important implications for the mechanisms behind SEP acceleration
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All authors Xuchun Duan, Ting Li, Yingli Cui, Yijun Hou, Chuan Li, Nicolas Wijsen, Zelong Jiang, Yihua Yan, Suli Ma, Zheng Sun

Earth and Planetary Astrophysics

Sub-Neptunes Show a Stronger Correlation with Cold Jupiters than Super-Earths Especially in Metal-rich Systems

Di-Chang Chen, Fei Dai, Bo Ma et al. (+2 more)

Correlations between the inner small planets and cold giants encodes the formation and evolution of planetary systems. It remains unclear if the correlation differs on the two sides of the radius valley. In this work, we compute the conditional frequency of cold Jupiters in systems with only inner sub-Neptunes $P(\rm CJ|SN)$ and those with only inner super-Earths $P(\rm CJ|SE)$. We find that, around transiting sample around metal-rich stars, $P(\rm CJ|SN, [Fe/H]>0)$ and $P(\rm CJ|SE, [Fe/H]>0)$ are $42.6^{+10.6}_{-9.9}\%$ and $14.5^{+12.7}_{-6.9}\%$. Comparing with the field giant frequency ($14.3^{+2.0}_{-1.8}\%$), we show that inner sub-Neptunes and cold Jupiters exhibit a significant positive correlation for metal-rich systems with a confidence level of 99.95%, whereas this correlation is absent for systems with super-Earths. We also consider a homogeneous Kepler-Keck subsample and derive similar results, with $P(\rm CJ|SN, [Fe/H]>0)$ of $45.8^{+18.6}_{-16.3}\%$ and $P(\rm CJ|SE, [Fe/H]>0)$ of $13.3^{+17.0}_{-6.8}\%$. Radial velocity sample shows consistent results, with metal-rich systems hosting massive inner planets exhibiting a strong positive correlation (confidence level of 99.11%) with outer cold Jupiters ($P(\rm CJ|M_{p}>10M_\oplus, [Fe/H]>0) = 34.6^{+11.0}_{-9.1}\%$). These results can be naturally understood since metal-rich disks are expected to more efficiently produce both outer cold Jupiters and inner planets with larger radii and masses. Our findings highlight the critical role of stellar metallicity in shaping planetary architectures, particularly for large/massive planets.
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All authors Di-Chang Chen, Fei Dai, Bo Ma, Shang-Fei Liu, Cong Yu