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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 15 December

High Energy Astrophysical Phenomena

The First X-Ray Polarimetry of an Eclipsing Low-Mass X-Ray Binary: Serendipitous IXPE Observation of AX J1745.6-2901

Romana Mikušincová, Lorenzo Marra, Hemanth Manikantan et al. (+38 more)

We present the first X-ray polarimetric measurement of the neutron star low-mass X-ray binary system AX J1745.6-2901 conducted by the Imaging X-ray Polarimetry Explorer (IXPE) satellite. This transient source, located within $ \sim $1.5' of the Galactic center, was observed serendipitously during a MAXI J1744-294 observation with a duration of 150 ks. The complex nature of the region in which AX J1745.6-2901 is located poses a challenge for studying its polarization. By performing a detailed analysis of the contamination from MAXI J1744-294 and the Galactic center diffuse emission, we find the source polarization degree PD = 14.7$\% \pm$ 4.0$\%$ and polarization angle PA = 122$^\circ \pm 8^\circ$. The phase-resolved analysis shows increase in polarization during the eclipse phase, with PD = 34.2$\% \pm$ 8.7$\%$, suggesting that the polarization-inducing mechanisms are of scattering nature, probably originating from disk winds.
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All authors Romana Mikušincová, Lorenzo Marra, Hemanth Manikantan, Stefano Bianchi, Fiamma Capitanio, Sudip Chakraborty, Raul Ciancarella, Enrico Costa, Nicolas De Angelis, Melania Del Santo, Sergio Fabiani, Riccardo Ferrazzoli, Vittoria E. Gianolli, Andrea Gnarini, Adam Ingram, Shifra Mandel, Guglielmo Mastroserio, Giorgio Matt, Kaya Mori, Fabio Muleri, Simone Pagliarella, Maxime Parra, P. O. Petrucci, Jakub Podgorný, Juri Poutanen, Swati Ravi, Paolo Soffitta, James F. Steiner, Antonella Tarana, Roberto Taverna, Francesco Ursini, Alexandra Veledina, Federico M. Vincentelli, Anastasiya Yilmaz, Barbara De Marco, Maitrayee Gupta, Vladislav Loktev, Thomas D. Russell, Jiří Svoboda, Francesco Tombesi, Shuo Zhang

High Energy Astrophysical Phenomena

Multiband gravitational wave observations of eccentric escaping binary black holes from globular clusters

Yuetong Zhao, Abbas Askar, Youjun Lu et al. (+7 more)

Stellar-mass binary black holes (sBBHs) formed in globular clusters (GCs) are promising sources for multiband gravitational wave (GW) observations, particularly with low- and middle-frequency detectors. These sBBHs can retain detectable eccentricities when they enter the sensitivity bands of low-frequency GW observatories. We study multiband GW observations of eccentric sBBHs that escape from GC models simulated with the MOCCA code, focusing on how low- and middle-frequency detectors can constrain their eccentricities and other parameters. Using Monte Carlo simulations, we generate ten realizations of cosmic sBBHs by combining the MOCCA sample with a cosmological model for GC formation and evolution. We then assess their detectability and the precision of parameter estimation. Our results show that LISA, Taiji, the LISA-Taiji network (LT), and AMIGO could detect $0.8\pm0.7$, $11.6\pm2.0$, $15.4\pm2.7$, and $7.9\pm1.3$ escaping sBBHs, respectively, over four years, while LT-AMIGO could detect $20.6\pm3.0$ multiband sBBHs in the same period. LT and AMIGO can measure initial eccentricities with relative errors of approximately $10^{-6}-2\times10^{-4}$ and $10^{-3}-0.7$, respectively. Joint LT-AMIGO observations have a similar ability to estimate eccentricities as LT alone.
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All authors Yuetong Zhao, Abbas Askar, Youjun Lu, Zhoujian Cao, Mirek Giersz, Grzegorz Wiktorowicz, Arkadiusz Hypki, Lucas Hellstrom, Sohaib Ali, Wei-Tou Ni

Astrophysics of Galaxies

Mapping the Ages of Stars with Chemistry

Carlos Viscasillas Vázquez, Giada Casali, Laura Magrini et al. (+11 more)

Chemical clocks, based on age-sensitive stellar abundance ratios, offer a powerful and scalable approach to reconstruct the formation history of the Milky Way. This white paper outlines how wide-field, high-resolution spectroscopy can transform chemical clocks into precise and broadly applicable stellar age estimators when combined with astrometry and asteroseismology. We summarize the current limitations, including calibration across Galactic environments and the impact of internal stellar evolution, and define the observational requirements needed to overcome them. The Wide-field Spectroscopic Telescope (WST), with its large field of view, high multiplex, and broad wavelength coverage at high spectral resolution, is uniquely suited to deliver the homogeneous datasets required to map the age structure of the Galaxy at unprecedented scale. Such a capability will enable decisive progress in Galactic archaeology and stellar evolution studies.
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All authors Carlos Viscasillas Vázquez, Giada Casali, Laura Magrini, Gabriele Cescutti, Sergio Cristallo, Camilla Danielski, Riano Giribaldi, Georges Kordopatis, Ivan Minchev, Marta Molero, Andrés Moya, Marco Palla, Gražina Tautvaišienė, Diego Vescovi

Solar and Stellar Astrophysics

VLBI astrometry of radio stars to link radio and optical celestial reference frames - II. 11 radio stars

Jingdong Zhang, Bo Zhang, Shuangjing Xu et al. (+10 more)

The alignment between the radio-based International Celestial Reference Frame (ICRF) and the optical Gaia Celestial Reference Frame (Gaia-CRF) is critical for multi-waveband astronomy, yet systematic offsets at the optical bright end (G<13) limit their consistency. While radio stars offer a potential link between these frames, their utility has been restricted by the scarcity of precise Very Long Baseline Interferometry (VLBI) astrometry. In this study, we present new VLBI astrometry of 11 radio stars using the Very Long Baseline Array (VLBA), expanding the existing sample with positions, parallaxes, and proper motions measured. All 11 radio stars were detected, for 10 of which parallaxes and proper motions can be estimated, achieving median uncertainties better than 0.1 mas and 0.1 mas/yr, respectively. These new samples greatly contribute to the link between ICRF and Gaia-CRF at the optical bright end.
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All authors Jingdong Zhang, Bo Zhang, Shuangjing Xu, Xiaofeng Mai, Mark J. Reid, Pengfei Jiang, Wen Chen, Fengchun Shu, Jinling Li, Lang Cui, Xingwu Zheng, Yan Sun, Zhaoxiang Qi

Solar and Stellar Astrophysics

WZ Sge-type dwarf novae: an extreme laboratory in cataclysmic variables

Yusuke Tampo

WZ Sge-type dwarf novae form one of the most intriguing classes of compact accreting binaries. They are recognized as the most evolved population of hydrogen-rich cataclysmic variables. Yet they exhibit energetic disk-powered outbursts with an amplitude of 6-9 mag, duration of a month, and decade-long outburst cycles. Despite the dramatic increase in the number of WZ Sge stars over the last decades, there are many unresolved questions, both in terms of their binary evolution and outburst mechanism. In this proceeding paper, I review the recent studies on WZ Sge stars, focusing on their outbursts. Recent observations, both photometrically and spectroscopically, have found the absence of enhanced emission from the hotspot during the early outburst rise in WZ Sge stars, casting doubt on the occurrence of the enhanced mass transfer. Meanwhile, several WZ Sge stars are newly suggested to harbor a magnetic white dwarf, inferring an inner disk truncation in quiescence. Diversity among systems has been discovered: a WZ Sge star with superoutbursts both accompanying and lacking an early superhump phase, one possibly harboring an ONe and massive white dwarf, and one showing optical spectra strongly affected by disk winds. I introduce the connections of WZ Sge stars to period bouncers, helium-rich AM CVn stars, and low-mass X-ray binaries. Finally, prospects of WZ Sge stars in the upcoming time-domain surveys, such as the Rubin Observatory LSST, are presented.
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High Energy Astrophysical Phenomena

Revisiting the role of the streaming instability for the cosmic-ray spectrum in the GeV to TeV range

Linh Han Thanh, Julien Dörner, Horst Fichtner et al. (+2 more)

A complete understanding of the cosmic-ray energy spectrum remains a challenge to theory that must be met by comprehensive modeling efforts. One of these is the subject of the present study, namely, an explanation of the recently discovered spectral hardening at $\sim 300$ GeV with self-consistently treated cosmic-ray diffusion, where self-generated waves resulting from the streaming instability impact the diffusion of high-energy particles. We revisit the corresponding model by Blasi et al. (2012), perform an extensive parameter study, and determine an optimal range of parameters that best fit the cosmic-ray data. We conclude that self-consistently treated cosmic-ray transport remains a competitive alternative to explain the spectral hardening of the cosmic-ray energy spectrum at a few hundred GeV.
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All authors Linh Han Thanh, Julien Dörner, Horst Fichtner, Julia Becker Tjus, Elena Amato

High Energy Astrophysical Phenomena

Transitional Dynamics: Unveiling the Coexistence and Interplay of Type-B and Type-C QPOs in MAXI J1348-630

Xinlei Wang, Zhen Yan, Fu-Guo Xie et al. (+3 more)

Based on broadband timing analysis of Insight-HXMT and NICER data from the 2019 outburst of the black hole X-ray binary (BHXRB) MAXI J1348-630, we report the detection of the coexistence and competitive interplay between type-C and type-B quasi-periodic oscillations (QPOs). Specifically, the two QPO types were detected simultaneously but exhibited distinct energy dependencies: the type-C QPO was dominant in the hard X-ray band (10-30 keV), while the type-B QPO was more prominent in the soft X-ray band (1-10 keV). Further analysis reveals that the emergence of the type-C QPO suppresses the strength of the type-B QPO, particularly above 10 keV. Tracking the detailed evolution of these QPOs, we find that the weakening of the type-B QPO coincides with the strengthening of the type-C QPO, indicating a competitive interaction between them. These findings reveal a more complex relationship between type-B and type-C QPOs than previously recognized, suggesting they originate from distinct but interacting physical components within the accretion flow and/or jet, and providing new insights into the dynamics of accretion state transitions.
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All authors Xinlei Wang, Zhen Yan, Fu-Guo Xie, Jun-Feng Wang, Ya-Xing Li, Ren-Yi Ma

Astrophysics of Galaxies

Simulating the spatial distributions of gas- and ice-phase molecules in galaxies: a new method and preliminary results

K. Bekki, K. Furuya and T. Shimonishi

Recent observations have revealed significant variations in the abundances of gas- and ice-phase molecules in galaxies with different luminosities and types. In order to discuss the physical origins of these variations, we incorporate gas- and dust-phase interstellar chemistry into galaxy-scale simulations with various baryonic physics including dust formation, evolution, and destruction, all of which are essential for the calculations of 400 interstellar molecule species. The new simulations can accordingly predict the abundances of gas- and ice-phase molecular species such as H_2O and CO_2 ice within individual molecular gas cloud of galaxies based on gas density and temperature, dust temperature (T_dust), elemental abundances (e.g., CHNOPS), UV radiation strength (F_UV), and cosmic ray ionisation rate (zeta_CR) within the clouds. Since this is the first of the series of papers, we describe the details of the new simulations and present the preliminary results focused on the spatial distributions of H_2O, CO, CO_2, and CH_3OH ice species in a disk galaxy similar to the Milky Way. We particularly discuss how T_dust and gas-phase elemental abundances can control the spatial distributions of the above molecules in galaxies. We briefly discuss the total amount of H_2O and CO_2 ices and radial distributions of PN and PO molecules in the Galaxy.
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Astrophysics of Galaxies

A New Catalog of Head Tail Radio Galaxies from the VLA FIRST Survey

Tapan K. Sasmal, Soumen Bera, Sabyasachi Pal et al. (+1 more)

The head–tail (HT) morphology of radio galaxies is seen for a class of radio sources where the primary lobes are being bent in the intercluster weather due to strong interactions between the radio jets and their respective intracluster medium. A systematic search has been carried out for new HT radio galaxies from the Very Large Array Faint Images of the Radio Sky at Twenty-Centimeters survey database at $1400\,\mathrm{MHz}$. Here, we present a catalog of 717 new HT sources, among which 287 are narrow-angle tail (NAT) sources whose opening angle between the two lobes is less than $90^\circ$, and 430 are wide-angle tail (WAT) whose opening angle between the two lobes is greater than $90^\circ$. NAT radio sources are characterized by tails bent in a narrow “V”-like shape; the jet bending in the case of WAT radio galaxies are such that the WATs exhibit wide “C”-like morphologies. Optical counterparts are found for 359 HT sources. We report HT sources with luminosity ranges $10^{38} \lesssim L_{1.4\,\mathrm{GHz}} \lesssim 10^{45}\,\mathrm{erg\,s^{-1}}$ and redshifts up to 2.01. The various physical properties of these HT sources are mentioned here. Some statistical studies have been done for this large number of newly discovered HT sources.
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All authors Tapan K. Sasmal, Soumen Bera, Sabyasachi Pal, Soumen Mondal

High Energy Astrophysical Phenomena

Redshift Classification of Optical Gamma-Ray Bursts using Supervised Learning

Milind Sarkar, Maria Giovanna Dainotti, Nikita S. Khatiya et al. (+8 more)

Modern satellite missions localize many gamma-ray bursts (GRBs), but spectroscopic redshifts remain scarce because rapid optical follow-up is often unavailable. Optical plateau classification differs fundamentally from its X-ray counterpart: heterogeneous ground-based follow-up, dust extinction, and chromatic afterglow behavior introduce greater incompleteness than in the X-ray data. We present a supervised machine-learning classification of long-duration GRBs (duration $>$ 2 s) with measured redshifts and possessing optical plateau emission. As predictors, we combine plateau and prompt-emission observables. Using 171 such GRBs, we evaluate binary classification — whether a GRB is high- or low-$z$ — at thresholds $z_t = 2.0, 2.5$, and $3.0$. The best classifier, at $z_t = 2.0$, achieves a training-set true positive rate (TPR) of 0.741 and an area under the curve (AUC) of 0.841, with a train-to-test AUC difference within 4 percent. The novelty of this work is a classifier built on an optical-plateau-selected sample. Prompt-emission and absorption variables are favored over plateau parameters at $z_t = 2.0$ on the raw (complete-case) data with the Least Absolute Shrinkage and Selection Operator (LASSO), thus allowing a reliable classifier without waiting for the plateau signatures in the light curve. The X-ray absorption column density, $\log(\mathrm{NH})$, and the prompt-emission peak flux, $\log(\mathrm{PeakFlux})$, are stably selected by both the optical and X-ray classifiers. We publicly release a web-based application for the optical classifier, complementing the available X-ray classifier \citep{dainotti2025grbredshiftclassifierfollowup}, to help the community rapidly select high-$z$ GRBs for follow-up.
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All authors Milind Sarkar, Maria Giovanna Dainotti, Nikita S. Khatiya, Dhruv S. Bal, Malgorzata Bogdan, Ye Li, Agnieszka Pollo, Dieter H. Hartmann, Bing Zhang, Nissim Fraija, J. Xavier Prochaska

High Energy Astrophysical Phenomena

Flashing fast: characterising the 2025 outburst of MAXI J1957+032

A. Sanna, G. Illiano, M. C. Baglio et al. (+13 more)

MAXI J1957+032 is an accreting millisecond X-ray pulsar that shows brief, recurrent outbursts in an ultra-compact ~1 h orbit. We characterise the 2025 outburst using X-ray timing and spectroscopy from XMM-Newton and Swift (and a late-time NuSTAR observation), together with contemporaneous optical photometry from LCO, and compare the spin frequency with the 2022 outburst. Timing searches detect coherent pulsations at ~313.6 Hz with no measurable frequency derivative during the XMM-Newton exposure. Relative to its 2022 outburst, we measure a long-term spin-down of ~-2x10^-14 Hz s^-1, consistent with magnetic-dipole braking in quiescence. The pulse profile is nearly sinusoidal, with significant power at the fundamental, second, and fifth harmonics; the fractional amplitude decreases with increasing flux and shows soft lags up to a few keV. The 0.5-10 keV spectrum is well described by absorbed thermal Comptonisation (photon index ~2.4) plus a cool blackbody (kT ~0.23 keV) consistent with emission from a surface hotspot; no reflection or Fe-line features are detected. Requiring R_m \leq R_co implies B_s ~(0.5-3)x10^8 G for d=(5 \pm 2) kpc and {\xi}=0.3-0.5, below the upper limit from the secular spin-down (B_p \leq 10^9 G), possibly indicating a mildly leaky propeller. The optical emission lies on the neutron-star branch of the L_OIR-L_X relation, consistent with reprocessing in a compact disc. The optical SEDs are broadly flat, while an early red excess suggests a transient jet contribution during the initial hard X-ray phase; an optical peak delayed relative to the X-rays may trace an outward-propagating heating front and rapid disc evolution in these short-lived outbursts.
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All authors A. Sanna, G. Illiano, M. C. Baglio, D. M. Russell, A. Borghese, A. Miraval Zanon, A. Marino, A. Riggio, A. Papitto, K. Alabarta, T. Di Salvo, A. Anitra, L. Burderi, F. Lewis, R. Iaria, D. A. H. Buckley

High Energy Astrophysical Phenomena

The disk precession in a Be star-magnetar binary and its application to the rotation measure of FRB 20201124A

Ying-ze Shan, Wei-Hua Lei, Hao-Tian Lan et al. (+7 more)

Fast radio bursts (FRBs) are bright, millisecond-duration radio bursts with poorly known origins. Most FRB sources are detected only once, while some are repeaters. Variation patterns observed in the rotation measure (RM) of some repeaters – indicate that the local magneto-ionic environments of these FRB sources are highly dynamic. It has been suggested that a Be star-magnetar binary system is a possible origin for such variation. FRB 20201124A is notable among these sources since it is the most active one and exhibits substantial temporal variations of RM measured by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The physics behind this long-term behavior is poorly understood. Here we propose that, within the framework of the Be star-magnetar binary scenario, the observed variation of RM is attributed to a combination of orbital motion and the precession of the circumstellar disk of the Be star. While a ~785-day precession of the disk contributes to the observed decrease in the amplitude of the variation, our model predicts that the amplitude oscillates with this period.
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All authors Ying-ze Shan, Wei-Hua Lei, Hao-Tian Lan, Shao-yu Fu, Jumpei Takata, Yuan-chuan Zou, Jia-xin Liu, Long-xuan Zhang, Tong-lun Wang, Fa-Yin Wang

High Energy Astrophysical Phenomena

X-ray Variability and Photosphere Evolution during Accretion Disk Formation in Tidal Disruption Events

Xiaoshan Huang, Maria Renee Meza, Sol Bin Yun et al. (+3 more)

The early time emission in tidal disruption events (TDEs) originates from both accretion and shocks, producing photons that eventually emerge from an inhomogeneous photosphere. We model disk formation following debris stream self-intersection in a TDE using three-dimensional, frequency-integrated and multi-group radiation hydrodynamic simulations. We find a more circularized disk forms about 24 days following the stream-stream collision, once the mass fallback rate passes its peak and the debris stream density decreases. Despite the absence of a circularized disk at early times, various shocks and the asymmetric photosphere are sufficient to drive a wide range of x-ray-to-optical ratios and soft-X-ray variability. We find that with strong apsidal precession, the first light is from the stream-stream collision. It launches an optically-thick outflow, but only produces modest prompt emission. The subsequent optical and ultraviolet (UV) light curve rise is mainly powered by shocks in the turbulent accretion flow close to the black hole. The optical-UV luminosity peaks roughly when the disk forms and shock-driven outflows subside. Radiation pressure clears the polar region and creates optically-thin channels. We obtain the broadband spectral energy distribution (SED) by post-processing multi-group simulations with 16-20 frequency groups. The SED has a black body component that peaks in the extreme UV. The soft X-ray component either resembles a thermal tail, or can be described by a power law associated with bulk Compton scattering. The blackbody parameters are broadly consistent with observed optical TDEs and vary weakly with viewing angle, but the soft X-ray emission is highly angle-dependent.
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All authors Xiaoshan Huang, Maria Renee Meza, Sol Bin Yun, Brenna Mockler, Shane W. Davis, Yan-fei Jiang

Astrophysics of Galaxies

DREAMS.II. Galaxy Demographics from Direct Te-Based Metallicities at z~2-10: Tracing the Evolution of the Mass-Metallicity and Fundamental Relations

Moka Nishigaki, Kimihiko Nakajima, Masami Ouchi et al. (+6 more)

We present the statistics of line ratios and direct Te-based metallicities from JWST medium-resolution spectra of 292 galaxies at z=2-10, combining DREAMS observations with those of JADES and CEERS. To remove systematics caused by stellar mass (M*) and star formation rate (SFR), we construct stacked spectra binned by redshift within fixed M* and SFR ranges, as well as across the full ranges. We find that the [OII]3727/Hb ratio drops by a factor of five from z~3 to 8 at fixed M* and SFR, in contrast to the nearly constant [OIII]5007/Hb ratio. We derive metallicities via the direct Te method using the [OIII]4363 line, and identify that high-z galaxies lie on the low-metallicity end of the anti-correlation between ionization parameter and metallicity at z~0. Photoionization modeling demonstrates that the redshift evolution, where metallicity decreases and ionization parameter increases, self-consistently explains the observed line ratios. We then examine the mass-metallicity (MZ) and fundamental (MZ-SFR) relations. Including additional galaxies at z~10-12, we find that the MZ relation monotonically decreases from z~3 to 10 at fixed M*, while the MZ-SFR relation shows a significant decline at z>8. Based on the ChemicalUniverseMachine model, this evolutionary trend can be explained by enhanced gas inflow (outflow) by a factor of ~5 (~1.7) at z>8.
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All authors Moka Nishigaki, Kimihiko Nakajima, Masami Ouchi, Peter Behroozi, Minami Nakane, Yui Takeda, Hiroya Umeda, Hidenobu Yajima, Hiroto Yanagisawa

Astrophysics of Galaxies

Kinematics of H I and O VI Absorbers: Insights into the Turbulence Driver of the Multiphase Circumgalactic Medium

Zhijie Qu, Hsiao-Wen Chen, Eliana Schiller et al. (+2 more)

We investigate large-scale gas kinematics in the multiphase circumgalactic medium (CGM) using the observed correlation between line width (Doppler $b$ parameter) and column density ($N$) for H I and O VI absorbers. Leveraging extensive public galaxy survey data at $z\lesssim0.1$, we construct a new galaxy sample based on the availability of background Quasi-Stellar Objects (QSOs) with far-ultraviolet spectra from the Far Ultraviolet Spectroscopic Explorer (FUSE). By combining this FUSE-galaxy sample with literature collections, we find that H I absorbers exhibit a clear inverse correlation between Doppler width and column density over nearly five orders of magnitude in $N_{\rm HI}$, from $N_{\rm HI} \approx 10^{13}\,\mathrm{cm^{-2}}$ to $N_{\rm HI} \approx 10^{18}\,\mathrm{cm^{-2}}$, while O VI absorption follows a positive correlation across $N_{\rm OVI}\approx 3\times10^{13}$-$10^{15}\,\mathrm{cm^{-2}}$.We develop a model framework to interpret these contrasting trends and show that H I absorbers are best described as systems of approximately constant total column density ($N_{\rm H}$), whereas O VI traces regions of roughly constant spatial density ($n_{\rm H}$ and $n_{\rm OVI}$). Under the latter scenario, the observed $b_{\rm OVI}$-$N_{\rm OVI}$ relation maps directly to a velocity-size relation consistent with a Kolmogorov-like turbulent spectrum. Together, these findings reveal a coherent physical picture in which H I and O VI trace a continuous turbulent cascade spanning more than five orders of magnitude in spatial scale-from cool, photoionized clumps to warm, highly ionized halo gas – with accretion in the halo outskirts likely driving the turbulent energy injection that sustains the multiphase CGM.
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All authors Zhijie Qu, Hsiao-Wen Chen, Eliana Schiller, Jing Wang, Max Gronke

Sunday 14 December

Instrumentation and Methods for Astrophysics

Evolving the Loeb Scale

Oem Trivedi and Abraham Loeb

We develop a differential formulation of the Loeb Scale that extends the original static framework into a radially evolving, real time classification scheme for interstellar objects. By promoting each anomaly metric to a function of heliocentric distance and introducing a relaxation equation for the effective score, our method incorporates memory, hysteresis and predictive capability. This allows us to have early, stable forecasts of an object's eventual Loeb level based on sparse data obtained at large distances, which is more helpful to quantify its true nature when near Earth.
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High Energy Astrophysical Phenomena

Super-Eddington Accretion Geometry: a Remarkable Stability of the Hidden Ultraluminous X-Ray Source Cygnus X-3

Romana Mikušincová, Alexandra Veledina, Fabio Muleri et al. (+112 more)

We report on the average and orbital phase-resolved polarization of Cyg X-3 in the hard state during the 2023 Imaging X-ray Polarimetry Explorer (IXPE) observational campaign. We find the polarization degree of $ 21.2 \pm 0.4 \% $ and polarization angle of $ 92.2 \pm 0.5^\circ $, well compatible with the first hard-state IXPE observation in 2022. As the observed polarization depends on both the accretion geometry and the X-ray emission mechanism, which we attribute to reflection from the optically thick envelope surrounding the central source, our result indicates that both are very stable on year-long timescale. We discuss time- and energy-dependent polarization properties and their implications for the geometry and stability of the accretion funnel.
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All authors Romana Mikušincová, Alexandra Veledina, Fabio Muleri, Raul Ciancarella, Andrzej Zdziarski, David A. Green, Michael McCollough, Henric Krawczynski, James F. Steiner, Michal Dovčiak, Varpu Ahlberg, Stefano Bianchi, Alessandro Di Marco, Javier A. García, Adam Ingram, Philip Kaaret, Timothy Kallman, Hu Kun, Fabio La Monaca, Alexander Lange, Vladislav Loktev, Guglielmo Mastroserio, Giorgio Matt, Razieh Emami, Pierre-Olivier Petrucci, Jakub Podgorný, Juri Poutanen, Ajay Ratheesh, Nicole Rodriguez, Jiří Svoboda, Francesco Tombesi, Francesco Ursini, Iván Agudo, Lucio A. Antonelli, Matteo Bachetti, Luca Baldini, Wayne H. Baumgartner, Ronaldo Bellazzini, Stephen D. Bongiorno, Raffaella Bonino, Alessandro Brez, Niccolò Bucciantini, Fiamma Capitanio, Simone Castellano, Elisabetta Cavazzuti, Chien-Ting Chen, Stefano Ciprini, Enrico Costa, Alessandra De Rosa, Ettore Del Monte, Laura Di Gesu, Niccolò Di Lalla, Immacolata Donnarumma, Victor Doroshenko, Steven R. Ehlert, Teruaki Enoto, Yuri Evangelista, Sergio Fabiani, Riccardo Ferrazzoli, Shuichi Gunji, Kiyoshi Hayashida, Jeremy Heyl, Wataru Iwakiri, Svetlana G. Jorstad, Vladimir Karas, Fabian Kislat, Takao Kitaguchi, Jeffery J. Kolodziejczak, Luca Latronico, Ioannis Liodakis, Simone Maldera, Alberto Manfreda, Frédéric Marin, Andrea Marinucci, Alan P. Marscher, Herman L. Marshall, Francesco Massaro, Ikuyuki Mitsuishi, Tsunefumi Mizuno, Michela Negro, Chi-Yung Ng, Stephen L. O'Dell, Nicola Omodei, Chiara Oppedisano, Alessandro Papitto, George G. Pavlov, Abel L. Peirson, Matteo Perri, Melissa Pesce-Rollins, Maura Pilia, Andrea Possenti, Simonetta Puccetti, Brian D. Ramsey, John Rankin, Oliver J. Roberts, Roger W. Romani, Carmelo Sgrò, Patrick Slane, Paolo Soffitta, Gloria Spandre, Douglas A. Swartz, Toru Tamagawa, Fabrizio Tavecchio, Roberto Taverna, Yuzuru Tawara, Allyn F. Tennant, Nicholas E. Thomas, Alessio Trois, Sergey S. Tsygankov, Roberto Turolla, Jacco Vink, Martin C. Weisskopf, Kinwah Wu, Fei Xie, Silvia Zane

Astrophysics of Galaxies

The Merian Survey: A Statistical Census of Bright Satellites of Milky Way Analogs

Yue Pan, Shany Danieli, Jenny E. Greene et al. (+10 more)

We present a statistical census of bright, star-forming satellite galaxies around Milky Way (MW) analogs using the first data release of the Merian Survey. Our sample consists of 393 MW analogs with stellar masses $10^{10.5} < M_{\star, \rm host} < 10^{10.9} M_\odot$ at redshifts $0.07 < z < 0.09$, all central galaxies of their own dark matter halos. Using photometric selection – including magnitude, color, angular size, photometric redshift, and size-mass cuts – we identify 793 satellite candidates around these 393 hosts. Our selection leverages two medium-band filters targeting H$\alpha$ and [O iii] emission, enabling a nearly complete sample of star-forming, Magellanic Clouds-like satellites with $M_{\star, \rm sat} \gtrsim 10^{8} M_\odot$. We find that $\sim80\%$ of hosts have 0-3 massive satellites, and $13\pm4\%$ have two satellites (similar to the MW). Satellite abundance correlates with total stellar mass, and we provide significantly improved statistics for the most massive satellites at $\log_{10}[M_{\star, \rm sat}/M_{\odot}] \gtrsim 10$. The completeness-corrected radial distribution is less centrally concentrated than an NFW profile. In contrast, the Milky Way satellites are more centrally concentrated than the 50% richest Merian systems, but are broadly consistent with the 50% most centrally concentrated Merian systems. Our results highlight the power of medium-band photometry for satellite identification and provide a key benchmark for studying satellite quenching, environmental effects, and hierarchical galaxy formation.
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All authors Yue Pan, Shany Danieli, Jenny E. Greene, Jiaxuan Li, Alexie Leauthaud, Erin Kado-Fong, Yifei Luo, Abby Mintz, Alyson Brooks, Song Huang, Annika H. G. Peter, Joy Bhattacharyya, Lee S. Kelvin

Earth and Planetary Astrophysics

Pre-perihelion detection of a wobbling high-latitude jet in the interstellar comet 3I/ATLAS

M. Serra-Ricart, J. Licandro and M. R. Alarcon

We present observations of the detection of a faint high-latitude jet in the inner coma of comet 3I/ATLAS that coincides with the broad plume detected in visible images along PA $280 \pm 10^{\circ}$. A detailed analysis shows that the jet was clearly detected on seven nights (2025, August~3, 5, 18, 19, 21, 24, and~29). The jet maintains an almost, though not perfectly, constant position angle (PA) throughout these epochs. High-precision PA measurements at a projected distance of 6000~km from the cometary optocenter reveal a periodic modulation centered at ~ 280 degrees, consistent with a high-latitude jet undergoing precessional motion around the sky-projected spin axis of the nucleus. This is the first periodic jet-angle modulation detected in an interstellar comet. The derived periodicity of $7.74 \pm 0.35$ h may imply a nucleus rotation period of $P_{\mathrm{rot}} = 15.48 \pm 0.70$ h if the jet originates from a single active source near one of the poles. This value is slightly shorter than the period of $P_{\mathrm{rot}} = 16.79 \pm 0.23$ h derived from the photometric time series. From the measured PA range, the sky-projected orientation of the spin axis is derived as $\mathrm{PA} = 280.7 \pm 0.2^{\circ}$
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Astrophysics of Galaxies

An Extremely-red, UV-bright, and Extended Galaxy at z~6 in PRIMER/UDS: An Early Massive Galaxy Caught Quenching after an Obscured Starburst?

Nadara Hudson, Ryan Endsley and John Chisholm

JWST continues to reveal an astonishing number of massive quiescent galaxies at $z>4$, with number densities $\gtrsim10\times$ higher than model predictions. NIRSpec spectra imply that many of these systems underwent intense starburst episodes (SFR$\,\gtrsim300M_\odot$/yr), though direct evidence of such starbursts in the Gyr largely comes from exceptionally rare dusty star-forming galaxies (DSFGs) selected in the far-infrared. Here, we report the discovery of an extremely red ($\beta=-0.6$) yet UV-bright (F115W = 26.0 mag) $z\sim6$ star-forming system selected as a Lyman-break galaxy (LBG) over $\approx$500 arcmin$^2$ of deep NIRCam imaging. This galaxy (UDS_43065) shows photometric colors implying a prominent Balmer break and strong H$\alpha$ emission, consistent with a dramatic burst of star formation (SFR$\,\approx\,500-1000\,M_\odot$/yr) occurring 5-10 Myr ago that formed 20-40% of its total stellar mass ($\approx1.5\times10^{10}M_\odot$) with little activity since. This galaxy is one of only two objects with $M_\ast>10^{10}M_\odot$ across our full sample of 813 $z\sim6$ star-forming LBGs, and the only galaxy with a confident extremely-red UV slope ($\beta>-1$). UDS_43065 is clearly resolved yet compact in F444W ($r_e=400\pm10$ pc) indicating a very high stellar mass surface density of log$(\Sigma_\mathrm{eff}/(M_\odot\,\mathrm{kpc}^{-2}))=10.25\pm0.13$ comparable to quenched $z\sim2-7$ galaxies. If the inferred star formation history (SFH) of UDS_43065 is corroborated with further observations, this object would seemingly represent a rarely-seen transitional phase between massive DSFGs and passive systems in the first Gyr, helping resolve the puzzling abundance of early massive quenched galaxies.
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Astrophysics of Galaxies

CAPOS: The bulge Cluster APOgee Survey XI. Unraveling the chemical composition of the bulge globular cluster NGC 6304

Carolina Montecinos, Doug Geisler, Cesar Muñoz et al. (+1 more)

Context. With CAPOS, we can mitigate the observational difficulties limiting access to bulge globular clusters in the optical and investigate them in more detail in the near-IR. Aims. To perform a rigorous abundance analysis of the metal-rich bulge globular cluster NGC 6304, in order to determine its detailed chemical composition and identify multiple populations. Methods. We analyzed APOGEE-2 near-IR spectra of 27 giant members. The abundances of 17 elements (C, N, O, Na, Mg, Al, Si, S, K, Ca, Ti, V, Cr, Mn, Fe, Ni, and Ce) were derived using the BACCHUS code, using atmospheric parameters from both ASPCAP and photometry (Gaia and 2MASS). Results. We derived $[{\rm Fe/H}] = -0.45\pm0.05$ using the ASPCAP parameters, and $[{\rm Fe/H}] = -0.45\pm0.08$ when using photometric parameters, with no evidence of an intrinsic metallicity spread. NGC 6304 shows $[\alpha/{\rm Fe}]_{\rm spec} = 0.24\pm0.07$ and $[\alpha/{\rm Fe}]_{\rm phot} = 0.23\pm0.08$. We find a significant spread in $[{\rm N/Fe}]$, with $\sigma_{\rm spec} = 0.54$ and $\sigma_{\rm phot} = 0.46$, along with a C-N anticorrelation. Furthermore, we detect a correlation of Ce with both N and Al, consistent with patterns observed in some metal-rich bulge globular clusters. Conclusions. We find a significant star-to-star variation in Na, but a minimal variation in O. The absence of the Mg-Al anticorrelation supports the evidence that the MgAl cycle is not active in globular clusters at high metallicity. The observed correlation between Ce and both N and Al suggests that the enrichment of these elements may be driven by asymptotic giant branch stars, positioning Ce as an element involved in multiple populations in metal-rich globular clusters. We find that abundances are consistent with those of bulge field stars of similar metallicity, suggesting a similar origin and chemical evolution.
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All authors Carolina Montecinos, Doug Geisler, Cesar Muñoz, Sandro Villanova

Solar and Stellar Astrophysics

Rotational evolution of slow-rotator sequence stars. II. Modeling the wind braking and the rotational coupling in the entire mass range of solar-like stars

F. Spada and A. C. Lanzafame

In recent years, ground- and space-based photometric surveys have characterized the rotational evolution of solar-like stars to an unprecedented level of detail. In this work we focus on the slow-rotator sequence, an emergent feature recognizable in the color-period diagram of Galactic open clusters. Understanding the evolution of this sequence is a promising avenue to formulate a robust rotation period-mass-age relation, which can be used to estimate stellar ages. Our model of the rotational evolution of stars on the slow-rotator sequence takes into account magnetized wind braking and the rotational decoupling between the radiative interior and the convective envelope. This decoupling naturally develops as the internal redistribution of angular momentum lags behind the loss of angular momentum at the stellar surface, and is parameterized in the model by a rotational coupling timescale. Using literature data on rotation and membership of stars in a selection of open clusters of age between 100 Myr and 4 Gyr, we constrain the mass dependence of the two competing processes of wind braking at the surface and angular momentum transport in the interior. Consistently with our previous findings, our best-fitting model requires a mass-dependent coupling timescale; this result is insensitive to the details of the wind braking model used. We show that the mass dependence of the coupling timescale follows a broken power-law in the entire solar-like mass range (0.4-1.25 Msun), with the exponent change occurring at ~ 0.6 Msun. At the same time, our approach can be used to infer semi-empirically the mass dependence of the wind braking model that best fits the observational constraints. Based on our findings, we propose a novel wind braking law with a particularly simple mass term, directly proportional to the moment of inertia of the convective envelope of the star.
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High Energy Astrophysical Phenomena

The TRAPUM Large Magellanic Cloud pulsar survey with MeerKAT II: 12 new discoveries and timing solutions for 7 pulsars

V. Prayag, L. Levin, M. Geyer et al. (+15 more)

We report the discovery of 12 new radio pulsars in the Large Magellanic Cloud (LMC) as part of the TRAPUM (TRAnsients and PUlsars with MeerKAT) Large Survey Project, using the MeerKAT L-band receivers (856–1712\,MHz). These pulsars, discovered in 18 new pointings with 2\,hour integration times, bring the total number of pulsars identified by this ongoing survey to 19 (yielding a total of 44 LMC radio pulsars now known), representing an 80 per cent increase in the LMC radio pulsar population to date. These include PSR\,J0454$-$6927, the slowest extragalactic radio pulsar discovered to date, with a spin period of 2238\,ms, and PSR\,J0452$-$6921, which exhibits the highest dispersion measure (DM) among extragalactic radio pulsars, at 326\,pc\,cm$^{-3}$. The fastest spin period among the new discoveries is 245\,ms, and the lowest DM is 62\,pc\,cm$^{-3}$. We also present timing results for our first pulsar discoveries with MeerKAT and the Murriyang radio telescope, obtaining phase-connected solutions for seven pulsars in the LMC. These results indicate that the pulsars are isolated, canonical radio pulsars with characteristic ages up to 8.8\,Myr
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All authors V. Prayag, L. Levin, M. Geyer, B. W. Stappers, H. Hurter, E. D. Barr, S. Buchner, M. Burgay, F. Calore, E. Carli, M. Colom i Bernadich, L. Gebauer-Werner, M. Kramer, P. V. Padmanabh, A. Ridolfi, T. Thongmeearkom, J. D. Turner, C. Venter

High Energy Astrophysical Phenomena

Disentangling AGN Feedback and Sloshing in the Perseus Cluster with XRISM: Insights from Simulations

Elena Bellomi, John A. ZuHone, Nhut Truong et al. (+10 more)

High-resolution X-ray spectroscopy with XRISM has revealed complex, non-monotonic velocity dispersion profiles in the Perseus cluster, pointing to a complex interplay between at least two physical drivers of motions caused by dynamical processes within the intracluster medium (ICM). To further explore this conclusion, we perform a suite of idealized, controlled simulations targeting the relative roles of merger-induced sloshing and active galactic nucleus (AGN) feedback. Our models systematically isolate and combine these mechanisms to predict observable velocity profiles and X-ray line shapes, providing direct comparison to XRISM and Hitomi data. We find that neither sloshing nor AGN activity alone can reproduce the observed velocity dispersion profile; only their combined action matches the elevated dispersions both at the cluster core and outskirts. Power-spectrum analysis reveals distinct spatial signatures: sloshing generates large-scale coherent motions, while AGN feedback injects turbulence and broadens the velocity spectrum at small scales, especially in the core. By forward-modeling spectral line profiles, we show how these dynamics imprint unique observational signatures on X-ray emission. Our results underscore the necessity of accounting for both large-scale and small-scale drivers of gas motions in the ICM when interpreting high-resolution spectroscopic data, and provide guidance for the analysis of forthcoming XRISM observations.
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All authors Elena Bellomi, John A. ZuHone, Nhut Truong, Irina Zhuravleva, Rainer Weinberger, Christoph Pfrommer, Congyao Zhang, Annie Heinrich, Mateusz Ruszkowski, Brian McNamara, Julie Hlavacek-Larrondo, Marie-Lou Gendron-Marsolais, Benjamin Vigneron

Astrophysics of Galaxies

EROS light curve data base

C. Afonso, J.-N. Albert, R. Ansari et al. (+18 more)

The EROS project (Expérience de Recherche d'Objets Sombres) carried out photometric surveys of dense stellar fields towards the Magellanic Clouds (LMC and SMC), the Galactic Bulge and Galactic spiral arms, over the period 1990-2003. The main goal of the experiment was to search for the Galactic Dark Matter in the form of massive compact objects (machos), through the gravitational microlensing effect. The historical record of the flux variations of the monitored stars by EROS-2 will be a unique asset for time domain astronomy and to complement current and future searches of transient sources. We describe the set of light curves obtained by EROS-2 program over the years 1996 to 2003, monitoring more than 86 million stars, which is publicly released through the Centre de Données de Strasbourg (CDS). The numbers of light curves in this data set are 28.7 and 4.0 million in LMC, respectively SMC, 42.9 million in the Galactic Bulge and 10.4 million towards the Galactic spiral arms, with several hundred measurements for each object. Data from EROS-1 is also being released. The object catalog and light curves and images are accessible through the CDS portal. This will be useful for checking the past behavior of newly discovered variable objects.
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All authors C. Afonso, J.-N. Albert, R. Ansari, E. Aubourg, J.P. Beaulieu, T. Blaineau, C. Coutures, F. Derue, J.F. Glicenstein, B. Goldman, C. Hamadache, T. Lasserre, L. Le Guillou, E. Lesquoy, C. Magneville, B. Mansoux, M. Moniez, N. Palanque-Delabrouille, O. Perdereau, J. Rich. M. Spiro, P. Tisserand

Solar and Stellar Astrophysics

Evolution Models of CO WD – AGB Star Merger Remnants

Chengyuan Wu, Heran Xiong, Shi Jia et al. (+2 more)

Common envelope evolution is a critical but still poorly understood phase in binary evolution. It plays a key role in forming close binaries such as hot subdwarfs, double white dwarfs, X-ray binaries, and double neutron stars. However, its outcomes remain highly uncertain. Depending on the efficiency of envelope ejection, a system may either survive as a close binary or undergo a complete merger. In this work, we investigate the post merger evolution of systems where a CO WD mergers with the core of an AGB star. A grid of merger remnant models with various core and envelope masses is constructed. At the onset of evolution, the CO core contracts and undergoes off-center carbon ignition, producing an inwardly propagating carbon flame. For remnants with relatively low mass of CO core, the flame phase is followed by core contraction and subsequent H-shell burning. For more massive CO cores, the carbon flame reaches the center and is soon followed by off-center neon burning, which is expected to eventually lead to core-collapse supernovae. The merger remnants occupy nearly the same region on HR diagram as ordinary AGB or super-AGB stars, exhibiting similar surface properties. Although their surface abundance may differ slightly from those of normal AGB stars depending on the initial core and envelope masses, these differences are strongly reduced once mass-loss is taken into account. We suggest that some giant-like stars, including candidates for Thorne-Zytkow objects (e.g., HV 2112), might alternatively be explained as AGB-WD merger remnants.
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All authors Chengyuan Wu, Heran Xiong, Shi Jia, Zhengyang Zhang, Bo Wang

High Energy Astrophysical Phenomena

DAO: A New and Public Non-Relativistic Reflection Model

Yimin Huang, Honghui Liu, Cosimo Bambi et al. (+4 more)

We present a new non-relativistic reflection model, DAO, designed to calculate reflection spectra in the rest frame of accretion disks in X-ray binaries and active galactic nuclei. The model couples the XSTAR code, which treats atomic processes, with the Feautrier method for solving the radiative transfer equation. A key feature of DAO is the incorporation of a high-temperature corrected cross section and an exact redistribution function to accurately treat Compton scattering. Furthermore, the model accommodates arbitrary illuminating spectra, enabling applications across diverse physical conditions. We investigate the spectral dependence on key physical parameters and benchmark the results against the widely used reflionx and xillver codes.
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All authors Yimin Huang, Honghui Liu, Cosimo Bambi, Adam Ingram, Jiachen Jiang, Andrew Young, Zuobin Zhang

High Energy Astrophysical Phenomena

Particle Acceleration in Magnetized Shear-Driven Turbulence

Mingxuan Liu, Mateusz Ruszkowski, Ellen Zweibel et al. (+5 more)

Shear flows, ubiquitous in space and astrophysical plasmas, can accelerate particles through turbulence excited by the Kelvin-Helmholtz instability. We present the first numerical study of particle acceleration in sustained, subsonic, non-relativistic, and magnetized turbulence driven purely by velocity shear, including full particle backreaction. Using two-dimensional MHD-PIC simulations with an initially uniform flow-aligned magnetic field and external stirring force, we demonstrate that, in this subsonic regime, sustained particle acceleration requires continuously driven turbulence, whereas freely decaying turbulence rapidly depletes its energy reservoirs and halts the acceleration. The acceleration mechanism operates through the systematic distortion of gyro-orbits by turbulent electric fields: acceleration phases extend the particle trajectory along the electric force, increasing the energy gain, while deceleration phases shorten the trajectory, reducing the energy loss. This asymmetry produces net energy gain despite stochastic fluctuations, with the mean energy change scaling quadratically with shear velocity, characteristic of second-order Fermi acceleration. Initially monoenergetic particles develop substantial non-thermal tails after the turbulence onset. The energization of particles that repeatedly cross shear layers follows geometric Brownian motion, yielding a log-normal distribution. High-energy particles exhibit pitch-angle anisotropy, becoming preferentially perpendicular to the flow-aligned magnetic field as their gyroradii exceed the turbulent layer width. These results establish shear-driven turbulence as a viable particle acceleration mechanism, providing a general model for particle energization in shear flows.
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All authors Mingxuan Liu, Mateusz Ruszkowski, Ellen Zweibel, Xiaochen Sun, Damiano Caprioli, Naixin Liang, Siang Peng Oh, Anatoly Spitkovsky

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

A parameterized equation of state for dark energy and Hubble Tension

Jing-Ya Zhao, Tong-Yu He, Jia-Jun Yin et al. (+2 more)

We propose a parameterized equation of state for dark energy and perform observational tests with the Hubble parameter measurements, the Pantheon supernova sample, and DESI DR2 data. We obtain the best-fit values for the parameters as: $H_0 = 73.28\pm 0.15~\mathrm{km\,s^{-1}\, Mpc^{-1}}$, $\Omega_{\rm m} = 0.316\pm 0.011$, and $\alpha = 0.00032\pm 0.00046$, demonstrating that the model exhibits a high degree of consistency with astronomical observations and provides a promising parameterized method for addressing the Hubble tension.
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All authors Jing-Ya Zhao, Tong-Yu He, Jia-Jun Yin, Zhan-Wen Han, Rong-Jia Yang

Solar and Stellar Astrophysics

Effects of the radiative interior on solar inertial modes

Suprabha Mukhopadhyay, Yuto Bekki, Xiaojue Zhu et al. (+1 more)

Solar inertial modes are believed to play important diagnostic and dynamical roles in the Sun's differentially rotating convection zone. However, the coupling of these modes to the radiative interior has not yet been discussed. We aim to understand the dependence of the modes on the uniformly rotating sub-adiabatic region below the convection zone and determine whether this leads to measurable changes at the surface. We used the Dedalus code to compute linear eigenmodes in the inertial frequency range in a setup that includes both the convection zone and the radiative interior down to $0.5R_\odot$. We imposed free-surface boundary conditions at both radial boundaries. For comparison, we also computed the eigenmodes in a setup restricted to the convection zone. We find that including the radiative zone only slightly modifies the frequencies and surface eigenfunctions, except for some modes with significant radial motion (high-frequency retrograde and prograde columnar modes). On the other hand, most modes penetrate significantly into the overshooting layer below the convection zone. This reduces their growth rates and distorts their eigenfunctions near the base of the convection zone. Furthermore, the uniformly rotating sub-adiabatic radiative zone supports oscillations due to Rossby modes of all possible spherical harmonics and radial nodes. In particular, when the nearest inertial mode in frequency space lies within around 10 nHz and shares the same north-south symmetry, these Rossby modes evolve into mixed modes characterized by significant motions within both the radiative and convection zones. However, such mixed modes have a high mode mass in the radiative interior and thus will be difficult to excite stochastically via convection.
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All authors Suprabha Mukhopadhyay, Yuto Bekki, Xiaojue Zhu, Laurent Gizon