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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 9 February

Cosmology and Nongalactic Astrophysics

Complementary Roles of Distance and Growth Probes in Testing Time-Varying Dark Energy

Seokcheon Lee

Distance measurements have long provided the primary observational constraints on the expansion history of the Universe and the properties of dark energy. However, because such observables depend on cumulative line-of-sight integrals over the Hubble rate, their sensitivity to time-dependent features of the dark energy equation of state is intrinsically limited. In this work, we examine this limitation from an information-based perspective using the eigenvalue structure of the Fisher information matrix constructed from distance, expansion rate, and growth observables. We show that distance and expansion-rate data generically produce a strongly hierarchical Fisher spectrum dominated by a single information mode, reflecting an irreducible loss of sensitivity to temporal variations in dark energy. This behavior can be traced directly to the integrated kernel structure of geometric observables. Growth measurements, by contrast, respond through differential dynamics and can introduce additional independent information directions. Using both controlled mock data and survey-like configurations representative of next-generation experiments, we find that the impact of growth information depends not only on its nominal precision but also on the structure of the data covariance. In simplified mock setups, growth measurements can partially activate a second information direction even at moderate precision. In Euclid-like configurations, however, the information remains effectively one-dimensional until growth precision reaches the percent level, below which a second mode emerges rapidly. These results clarify the complementary roles of distance and growth probes and provide a model-independent criterion for assessing the physical content of cosmological constraints on dynamical dark energy.
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Earth and Planetary Astrophysics

JWST spectral retrieval of cold directly imaged planet WD0806 b and the first measurement of altitude-dependent K$_{zz}$ in exoplanet atmospheres

Ben W.P. Lew, Thomas Roellig, Natasha E. Batalha et al. (+10 more)

WD0806 b is a rare exoplanet companion orbiting a white dwarf, currently with a projected orbital distance of 2500 au. The Spitzer mid-IR photometry suggests that the temperature is as cold as 350K, making it one of the coldest directly imaged exoplanets. In this paper, we present the Near-infrared Camera (NIRCam) F150W2, F200W, F356W, and F444W broadband photometry and a 3–5\um Near-Infrared spectroscopy (NIRSpec) G395M spectrum obtained with the James Webb Space Telescope (JWST). We develop a new retrieval framework based on the open-source PICASO software that includes additive and multiplicative systematic parameters. Our retrieval results reveal bounded abundances of H$_2$S, CO$_2$, CO, NH$_3$, H$_2$O, and CH$_4$. We present a new chemical analysis framework that utilizes retrieved abundances to measure altitude-dependent eddy diffusion coefficients (K$_{\mathrm zz}$) at multiple quenched pressures. We find that the eddy diffusion coefficients decrease from around $10^4$ to $10^2$ $\rm cm^2/s$ as the atmospheric pressure decreases from from 50 to 20 bars. To our knowledge, this is the first study to report altitude-dependent vertical mixing (or, equivalently, quenched-species-dependent vertical mixing) based on the measured molecular abundances of CO, CH$_4$, and CO$_2$. With the 1–21\um NIRCam, NIRSpec and the previously published MIRI data, we measure the bolometric luminosity to be log(L/L$_{\odot}$) = $-6.75\pm0.01$ and derive the mass to be $8\pm 1 \mathrm{M_J}$. The retrieval results suggest that \target has an elevated C/O ratio of 0.76, or 1.3$\times$ solar, sub-solar metallicity ([M/H ]= -0.25), and a nearly solar C/S ratio (1.17x solar).
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All authors Ben W.P. Lew, Thomas Roellig, Natasha E. Batalha, Nicholas F. Wogan, Thomas Greene, Mark S. Marley, Jonathan J. Fortney, Jarron Leisenring, Doug Johnstone, Matthew De Furio, Klaus Hodapp, Charles Beichman, Marcia Rieke

Sunday 8 February

High Energy Astrophysical Phenomena

A comprehensive catalogue of high-mass X-ray binaries in the Large Magellanic Cloud detected during the first eROSITA all-sky survey

D. Kaltenbrunner, C. Maitra, F. Haberl et al. (+9 more)

The Magellanic Clouds, the closest star-forming galaxies to the Milky Way, offer an excellent environment to study high-mass X-ray binaries. While the Small Magellanic Cloud has been thoroughly investigated with over 120 systems identified, the Large Magellanic Cloud has lacked a complete survey due to its large angular size. Most prior studies targeted central or high-star-formation regions. The SRG/eROSITA all-sky surveys now enable a comprehensive coverage of the LMC, particularly due to its close vicinity to the south ecliptic pole. This work aims to improve our understanding of the HMXB population in the LMC by building a flux-limited catalogue. This allows us to compare sample properties with those of HMXB populations in other nearby galaxies. Using detections during the first eROSITA all-sky survey, we cross-matched X-ray positions with optical and infrared catalogues to identify candidate HMXBs. We assigned flags based on multi-wavelength follow-up observations and archival data, using properties of known LMC HMXBs. These flags defined confidence classes for our candidates. We detect sources down to X-ray luminosities of a few $10^{34}$ erg s$^{-1}$, resulting in a catalogue of 53 objects, including 28 confirmed HMXBs and 21 new eROSITA detections. We identify several likely supergiant systems, including a candidate supergiant fast X-ray transient with phase-dependent flares. We find three Be stars with likely white dwarf companions. Two of the Be/WD candidates show steady luminosities across four eROSITA scans, unlike the post-nova states seen in the majority of previous Be/WD reports. Our catalogue is the first to cover the entire LMC since the ROSAT era, providing a basis for statistical population studies. Using the HMXB population, we estimate the LMC star-formation rate to be $(0.22^{+0.06}_{-0.07})$ M$_{\odot}$yr$^{-1}$, which is in agreement with other tracers.
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All authors D. Kaltenbrunner, C. Maitra, F. Haberl, J. Bodensteiner, D. Bogensberger, D. A. H. Buckley, M. R. L. Cioni, J. Greiner, I. Monageng, A. Udalski, G. Vasilopoulos, R. Willer

Solar and Stellar Astrophysics

Toward a Comprehensive Grid of Cepheid Models with MESA II. Impact of Physical and Numerical Assumptions on Elemental Abundances

O. Ziółkowska, R. Smolec, A. Thoul et al. (+2 more)

Modern tools for modeling stellar evolution, such as MESA (Modules for Experiments in Stellar Astrophysics), offer state-of-the-art implementations of stellar theories. However, this parametric approach introduces many free parameters that are often not constrained by observations. This is particularly important for evolved stars, like classical Cepheids, because uncertainties increase with evolution time. In previous work, we studied the effect of varying microphysics, including solar abundance mixtures, nuclear networks, atmosphere models, mixing-length prescriptions, treatments of convective boundaries, and numerical setup on evolutionary tracks. Here, we extend this analysis to the surface abundances of the dominant elements H, He, C, N, O, Ne, and Mg. We establish a reference model and 22 variants for each mass and metallicity, evolving them from the Zero-Age Main Sequence to central helium exhaustion. Masses between 2 to 8 solar mass and metallicities Z=0.0014, 0.004, 0.014 are explored, spanning the range of classical Cepheids. Both canonical and overshooting models are computed and compared. We find that uncertainties in surface abundances are generally small, arising mainly from variations in the depth of the convective envelope during the first dredge-up. The size of the convective envelope is sensitive to many aspects, including mass and metallicity. The central C/O ratio, relevant for white dwarf evolution, can vary by about 0.15, driven largely by convective boundary treatments or by modifying the 12C(alpha,gamma)16O reaction rate during helium burning. Surface and central abundances for the considered models at several benchmark points during the evolution are provided online.
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All authors O. Ziółkowska, R. Smolec, A. Thoul, R. Singh Rathour, V. Hocdé

High Energy Astrophysical Phenomena

Pulsars and Millisecond Pulsars II: Deep diving into the Evolutionary Mechanisms

Maria Rah, Rainer Spurzem, Francesco Flammini Dotti et al. (+1 more)

This second paper in our series investigates the evolutionary mechanisms that shape pulsars and millisecond pulsars (MSPs) across different astrophysical environments. We focus on the physical processes that govern spin evolution, magnetic field decay, binary interactions, and recycling pathways. Using observational constraints together with theoretical models, we examine how accretion, magnetic braking, and dynamical encounters contribute to the long-term evolution of compact objects. We also explore how these mechanisms differ between the Galactic Field and Globular Clusters, where stellar densities and interaction rates vary significantly. By integrating insights from population studies and numerical tools such as NBODY6++GPU, CMC, and COMPASS, we aim to clarify the dominant channels that lead to the formation and transformation of pulsars and MSPs. Our results highlight key uncertainties in current models and outline the physical ingredients required for more accurate simulations of compact object evolution.
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All authors Maria Rah, Rainer Spurzem, Francesco Flammini Dotti, Areg Mickaelian

Instrumentation and Methods for Astrophysics

Particle hydrodynamics with accurate gradients: a comparison of different formulations

S. Rosswog

We compare here several modern versions of SPH with a particular focus on the impact of gradient accuracy. We examine specifically an approximation to the "linearly exact" gradients (aLE) with standard SPH kernel gradients and with linearly reproducing kernels (RPKs) that fulfill the lowest order consistency relations exactly by construction. Most of the explored SPH formulations use shock dissipation (i.e. artificial viscosity and conductivity) with slope-limited reconstruction and parameters that trigger on both shocks and noise. We also compare with a recent particle hydrodynamics formulation that uses both RPKs and Roe's approximate Riemann solver instead of shock dissipation. Not too surprisingly, we find that the shock tests are rather insensitive to the gradient accuracy, but whenever instabilities are involved the gradient accuracy plays a crucial role. The reproducing kernel gradients perform best, but they are closely followed by the much simpler aLE gradients. The Riemann solver approach has some (minor) advantages in the shock tests, but shows some resistance against instability growth and at low resolution the corresponding Kelvin-Helmholtz simulations show substantially slower instability growth than the best shock dissipation approaches. Based on the battery of benchmark tests performed here, we consider a shock dissipation approach with reproducing kernels (our versions $V_3$ and $V_5$) as best, but closely followed by a similar version ($V_2$) that uses the simpler and computationally cheaper aLE gradients.
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Earth and Planetary Astrophysics

Impact of embedded circumplanetary winds on the circumstellar disk: I. Reshaping the local accretion environment

Danilo Sepúlveda-Rojas, Pablo Benítez-Llambay and Simon Casassus

The existence of winds is among the uncertainties related to the growth of giant planets. Such circumplanetary outflows have been proposed to explain kinematic and chemical structures in protoplanetary disks. We investigate the immediate impact of circumplanetary outflows on the circumstellar disk environment, the planetary vicinity, and planetary growth. We performed three-dimensional hydrodynamic simulations using FARGO3D, implementing a parametric wind launched from the vicinity of an embedded planet. Although the imposed configurations for the outflows do not significantly alter the global structure of the disk, they do substantially redistribute material in the vicinity of the embedded planet. In particular, the wind redirects accretion flows from polar to equatorial latitudes, resulting in variable accretion patterns over time. Although the mass accretion rate variations depend on the efficiency of the outflows, their presence diminishes the accretion rate over time and the total mass reservoir within the Hill sphere and the planet's direct vicinity, potentially slowing or limiting planetary growth.
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Instrumentation and Methods for Astrophysics

DerivKit: stable numerical derivatives bridging Fisher forecasts and MCMC

Nikolina Šarčević, Matthijs van der Wild and Cynthia Trendafilova

DerivKit is a Python package for derivative-based statistical inference. It implements stable numerical differentiation and derivative assembly utilities for Fisher-matrix forecasting and higher-order likelihood approximations in scientific applications, supporting scalar- and vector-valued models including black-box or tabulated functions where automatic differentiation is impractical or unavailable. These derivatives are used to construct Fisher forecasts, Fisher bias estimates, and non-Gaussian likelihood expansions based on the Derivative Approximation for Likelihoods (DALI). By extending derivative-based inference beyond the Gaussian approximation, DerivKit forms a practical bridge between fast Fisher forecasts and more computationally intensive sampling-based methods such as Markov chain Monte Carlo (MCMC).
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High Energy Astrophysical Phenomena

Pulsars and Millisecond Pulsars I: Advancements, Open Questions and finding Gaps via statistical insights

Maria Rah, Areg Mickaelian, Francesco Flammini Dotti et al. (+1 more)

We present a statistical study of pulsars and millisecond pulsars (MSPs) based on multiwavelength observations in the Galactic Field and Globular Clusters. We examine their emission properties, timing behavior, and spatial distributions, and discuss how theoretical models are required to interpret these observational trends. We focus on the magnetic field spin relation, including spin up through accretion in binaries and spin down driven by magnetic dipole radiation. Using numerical tools such as NBODY6++GPU, CMC, and COMPASS, we explore how dynamical interactions and binary evolution shape the properties of compact objects. Despite major progress, several open questions remain regarding binary interactions, magnetic field evolution, and the incorporation of pulsar physics into large scale simulations. Our analysis highlights the need for improved modeling frameworks to better understand the formation pathways and long term evolution of pulsars and MSPs.
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All authors Maria Rah, Areg Mickaelian, Francesco Flammini Dotti, Rainer Spurzem

Instrumentation and Methods for Astrophysics

SOLO: wide-field asteroid light curve monitoring system for SPHEREx

Bumhoo Lim, Seungwon Choi, Yoonsoo P. Bach et al. (+8 more)

We present the Solar system Objects Light curve Observatory (SOLO), a wide-field, high-cadence optical survey system designed to obtain absolutely calibrated asteroid light curves, converted to the Gaia G-band photometric system, in support of the SPHEREx Solar System Object Catalog (SSOC). SOLO was installed at the Sierra Remote Observatories (SRO) in California, USA, in July 2025 and is optimized for continuous, multi-night monitoring of asteroid brightness variations. We describe the system configuration, remote operation, and data reduction pipeline, and evaluate its optical and photometric performance using commissioning data. SOLO achieves stable photometric calibration across the 11.6 deg^2 field of view and reaches a 10-sigma limiting magnitude of G ~ 17.5 for a 180 sec exposure. Sample asteroid light curves obtained over multiple nights demonstrate consistent absolute photometry at the same rotational phase, validating the estimated performance. Finally, we outline the planned operational use of SOLO in connection with NASA's SPHEREx mission. Full science operations of SOLO are scheduled to begin in January 2026. Using these data, we aim to obtain on the order of 10^3 absolutely calibrated asteroid light curves per year in the Gaia G-band, which will be used to support the construction and scientific utilization of the SPHEREx SSOC.
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All authors Bumhoo Lim, Seungwon Choi, Yoonsoo P. Bach, Masateru Ishiguro, Sunho Jin, Carey M. Lisse, Max Mahlke, Jooyeon Geem, Jinguk Seo, Sihu Ahn, Hangbin Jo

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Dynamic Black-hole Emission Tomography with Physics-informed Neural Fields

Berthy T. Feng, Andrew A. Chael, David Bromley et al. (+3 more)

With the success of static black-hole imaging, the next frontier is the dynamic and 3D imaging of black holes. Recovering the dynamic 3D gas near a black hole would reveal previously-unseen parts of the universe and inform new physics models. However, only sparse radio measurements from a single viewpoint are possible, making the dynamic 3D reconstruction problem significantly ill-posed. Previously, BH-NeRF addressed the ill-posed problem by assuming Keplerian dynamics of the gas, but this assumption breaks down near the black hole, where the strong gravitational pull of the black hole and increased electromagnetic activity complicate fluid dynamics. To overcome the restrictive assumptions of BH-NeRF, we propose PI-DEF, a physics-informed approach that uses differentiable neural rendering to fit a 4D (time + 3D) emissivity field given EHT measurements. Our approach jointly reconstructs the 3D velocity field with the 4D emissivity field and enforces the velocity as a soft constraint on the dynamics of the emissivity. In experiments on simulated data, we find significantly improved reconstruction accuracy over both BH-NeRF and a physics-agnostic approach. We demonstrate how our method may be used to estimate other physics parameters of the black hole, such as its spin.
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All authors Berthy T. Feng, Andrew A. Chael, David Bromley, Aviad Levis, William T. Freeman, Katherine L. Bouman

Cosmology and Nongalactic Astrophysics

Self-resonance preheating in deformed attractor models: oscillon formation and evolution

Bao-Min Gu, Yu-Peng Zhang, Fu-Wen Shu et al. (+1 more)

It is well known that, in potentials that are quadratic near the minimum but shallower away, such as small-$\alpha$ ($\alpha \ll M_P^2$) attractors, the inflaton condensate fragments into localized compact objects known as oscillons during self-resonance preheating. In this work, we investigate self-resonance in a deformed $\alpha$-attractor T-model with a Gaussian feature near the minimum, distant from the end of inflation. Linear analysis reveals altered resonance bands and deformed Floquet charts dependent on feature parameters, primarily through the localized modification of $V''(\phi)$. In fully nonlinear lattice simulations, we find that the potential feature has only a modest influence on gradient-energy transfer during resonance, whereas the subsequent evolution becomes strongly dependent on the Gaussian feature's dimensionless amplitude $h$. Increasing $|h|$ suppresses the formation and persistence of compact oscillons, resulting in fewer objects and a smaller fraction of energy stored in them. The total-energy and internal-gradient-energy diagnostics give consistent lifetime trends. Within the directly resolved range, the oscillon lifetime decreases nonlinearly with increasing $|h|$, with negative $h$ generally producing shorter lifetimes than positive $h$ of the same magnitude. The gravitational wave emission is dominated by the resonant stage and becomes strongly suppressed after oscillon formation. We further find an enhancement in the high-frequency tail of the spectrum, sourced by the potential feature. Although a complete reheating description requires external couplings and higher-resolution simulations, clear qualitative differences in the post-inflationary expansion history already emerge within our simulated time window. These results clarify how potential features affect preheating dynamics and oscillon evolution.
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All authors Bao-Min Gu, Yu-Peng Zhang, Fu-Wen Shu, Yu-Xiao Liu

Cosmology and Nongalactic Astrophysics

Scalar-induced gravitational waves and primordial black holes from a localized bump or dip feature in a single-field inflationary potential

Xiang Zhang and Zhao-Huan Yu

We study the production of scalar-induced gravitational waves and primordial black holes in a single-field inflation model with a localized bump or dip feature in the potential. Introducing such a localized feature temporarily decelerates the slow-roll inflaton, amplifying the primordial curvature power spectrum into a sharp peak. Consequently, this enhancement sources a significant stochastic background of gravitational waves and leads to abundant formation of primordial black holes. Through eight benchmark cases, we show that the predicted abundances of primordial black holes can remain compatible with current observational limits, while the corresponding gravitational wave spectra peaking across a wide range of frequencies are accessible to future gravitational wave experiments in multiple observational bands.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th

New solution to the hyperon puzzle of neutron stars: Quantum many-body effects

Hao-Fu Zhu, Guo-Zhu Liu, Xufen Wu et al. (+1 more)

The hyperon puzzle refers to the challenge of reconciling the existence of hyperons in neutron star cores and the observed high masses of neutron stars. The recent discovery of PSR J0952-0607 ($2.35\pm0.17 M_{\odot}$) has intensified this challenge. Existing solutions fail to achieve such a high mass, and often predict unrealistically fast cooling that is at odds with observations. Here, we propose a novel solution to the hyperon puzzle. Using the Dyson-Schwinger equation approach, we incorporate the quantum many-body effects caused by strong baryon-meson interactions into the equation of state for cold baryonic matter and find it stiff enough to support a maximum hyperon-star mass of $M_{\mathrm{max}} \approx 2.59 M_{\odot}$, which can explain all the observed high neutron-star masses. The resulting proton and hyperon fractions are remarkably low, thus the nucleonic and hyperonic direct Urca processes are significantly suppressed. As a result, fast cooling typically does not occur in ordinary neutron stars.
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All authors Hao-Fu Zhu, Guo-Zhu Liu, Xufen Wu, Ye-Fei Yuan

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

Accelerating Black Hole Image Generation via Latent Space Diffusion Models

Ao Liu, Xudong Zhang, Lin Ding et al. (+3 more)

Interpreting horizon-scale black hole images currently relies on computationally intensive General Relativistic Ray Tracing (GRRT) simulations, which pose a significant bottleneck for rapid parameter exploration and high-precision tests of strong-field gravity. We demonstrate that physically accurate black hole images, synthesized from magnetized accretion flows, inherently reside on a low-dimensional manifold-encoding the essential features of spacetime geometry, plasma distribution, and relativistic emission. Leveraging this structure, we introduce a physics-conditioned diffusion model that operates in a compact latent space to generate high-fidelity black hole imagery directly from physical parameters. The model accurately reproduces critical observational signatures from full GRRT simulations-such as shadow diameter, photon-ring structure, and relativistic brightness asymmetry-while achieving over a fourfold reduction in computational expense. Compared with the previous generation of denoising diffusion models, the proposed approach achieves significant improvements in image quality, reconstruction fidelity, and parameter estimation accuracy, while reducing the average inference time per black hole image from 5.25 seconds to 1.15 seconds. Our work establishes diffusion-based latent models as efficient and scalable substitutes for traditional radiative transfer solvers, offering a practical framework toward real-time modeling and inference for next-generation black hole imaging.
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All authors Ao Liu, Xudong Zhang, Lin Ding, Cuihong Wen, Wentao Liu, Jieci Wang

Solar and Stellar Astrophysics

Twisted Pseudodisk and Asymmetric Mass Accretion on the Circumstellar Disk

Masahiro N. Machida, Shingo Hirano and Shantanu Basu

We model gas inflow patterns onto circumstellar disks and the evolution of the pseudodisk using three-dimensional resistive MHD simulations. Starting from a prestellar core without turbulence and with a misalignment between the initial magnetic field and rotation axis, the simulations are performed for $\sim10^5$ yr after protostar formation. After disk formation, the magnetic field around the disk becomes significantly distorted due to the disk rotational motion. Consequently, the structure of the pseudodisk also evolves into a complex morphology. As a result, both accretion onto the disk and outflow become asymmetric and anisotropic. Accretion to the disk occurs primarily through narrow-channel flows or streams. The time evolution of the infalling envelope leads to non-steady accretion onto the disk, which in turn causes variability in the mass accretion onto the central protostar. This study demonstrates that complex infalling envelope structures and channelized accretion flows onto the disk naturally arise even without assuming turbulence or external asymmetric inflows.
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Saturday 7 February

Earth and Planetary Astrophysics

Dynamical Mass Constraints on Transition Disk Perturbers with the G23H Catalog

Dori Blakely, William Thompson, Doug Johnstone et al. (+14 more)

We present dynamical mass constraints on perturbers in 11 transition disk systems using a novel combination of calibrated Hipparcos and Gaia absolute astrometry data. Out of the sample of 11, we find support for companions in four systems, with significant detections in two. These systems are: HD 142527, where we clearly detect the known low-mass stellar companion HD 142527 B and MWC 758, where we detect a likely sub-stellar companion. We also find moderate evidence of companions to AB Aur and UX Tau A. For the seven systems with non-detections, we find no evidence for companions more massive than $\sim$12 $M_{\mathrm{Jup}}$ with a semi-major axis greater than 3 au for both HD 100546 and HD 100453, nor for companions more massive than $\sim$3 $M_{\mathrm{Jup}}$ with a semi-major axis greater than 2 au for TW Hya. We also find no evidence for stellar mass companions with semi-major axes between $\sim$4 and $\sim$25 au for HD 34282, HD 97048, CQ Tau and RY Lup. In addition to our fiducial model, we perform cross validation between astrometry sources. By comparing results across models, we find tentative evidence of a short timescale excess astrometric noise that may impact some protoplanetary disk systems. We conclude with predictions for the prospects of making dynamical mass constraints on protoplanets in protoplanetary disk systems with Gaia data release 4 using detailed simulations of Gaia DR4 data of PDS 70 and WISPIT 2.
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All authors Dori Blakely, William Thompson, Doug Johnstone, Jessica Speedie, Jerry W. Xuan, Simon Blouin, Jingwen Zhang, Jean-Baptiste Ruffio, Eric Nielsen, Brendan P. Bowler, Kyle Franson, William Roberson, Ryan Cloutier, Andre Fogal, Kaitlyn Hessel, Christian Marois, Alexandra Rochon

High Energy Astrophysical Phenomena

A MeerKAT search for persistent radio sources towards twenty-five localised Fast Radio Bursts

Lebogang L. Mfulwane, James O. Chibueze, Thulo P. Letsele et al. (+17 more)

The discovery of persistent radio sources (PRSs) associated with repeating fast radio bursts (FRBs) has shed light on the immediate environments and possible progenitors of these FRBs. The confirmed PRSs may support the theory that FRB progenitors are compact central engines, whilst the non-detections suggest diversity of FRB's local environment. We perform a subarcsecond-resolution MeerKAT search at 1.28 GHz on 25 well-localised FRB positions provided by ASKAP and MeerTRAP. We detect 14 radio sources and provide flux upper limits for 12 non-detections (both these numbers include a source that was detected during two epochs of observation, and not detected during one epoch, adding up to 26). One radio source shows variability as seen in flux variations over three epochs of observation. Archival optical data reveal excesses in the direction of 13 detected radio sources. Similarly for four sources in the X-ray band, with one possibly being a high-energy signature of a radio galaxy core. Since we cannot definitively classify our detected radio sources as PRSs, future high-resolution observations with e-MERLIN will be required to resolve the radio emission and pronounce on the presence of compact PRSs associated with the 14 detected sources presented here.
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All authors Lebogang L. Mfulwane, James O. Chibueze, Thulo P. Letsele, Trevor M. Nyambe, Christo Venter, Mechiel Christiaan Bezuidenhout, Benjamin W. Stappers, Laura G. Spitler, Manisha Caleb, Adam Deller, Jéferson André Sales Fortunato, Bernardo Cornejo, Fabian Schüssler, Halim Ashkar, Frederica Bradascio, Surajit Kalita, Anu Kundu, Michael Kramer, Evan. F. Keane, Amanda Weltman

High Energy Astrophysical Phenomena

Effects of Viscosity on Sloshing Cold Fronts in Galaxy Clusters

Ming-Hsueh Hsieh, H.-Y. Karen Yang and John ZuHone

The viscous properties of the intracluster medium (ICM) remain poorly constrained. Cold fronts-sharp discontinuities formed during cluster mergers-offer a potential avenue to probe the effective viscosity of the ICM. Velocity shear across these fronts should generate Kelvin-Helmholtz instabilities (KHI), unless viscosity or magnetic tension suppresses them. We perform cluster merger simulations incorporating four ICM viscosity models: (A) inviscid, (B) isotropic Spitzer viscosity, (C) anisotropic Braginskii viscosity, and (D) Braginskii viscosity limited by microinstabilities. The isotropic Spitzer viscosity (case B) strongly suppresses KHI, producing smooth cold front surfaces, while the inviscid (A) and microinstability-limited (D) cases show prominent ripples. The Braginskii case (C) yields intermediate suppression. We also vary the plasma $\beta$ parameter ($\beta \approx$ 100 and 1600) to examine how a changing magnetic field strength affects the results. Stronger magnetic fields further suppress KHI, leading to smoother fronts and reduced differences between different viscosity models, while also widening the range of permitted pressure anisotropies when microinstability-based limiters are present. These results indicate that both viscosity and magnetic fields play crucial roles in stabilising sloshing cold fronts in galaxy clusters.
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Cosmology and Nongalactic Astrophysics

Cosmology with one galaxy: An analytic formula relating $\Omega_{\rm m}$ with galaxy properties

Kito Liao, Francisco Villaescusa-Navarro, Romain Teyssier et al. (+1 more)

Standard cosmological analyses typically treat galaxy formation and cosmological parameter inference as decoupled problems, relying on population-level statistics such as clustering, lensing, or halo abundances. However, classical studies of baryon fractions in massive galaxy clusters have long suggested that gravitationally bound systems may retain cosmological information through their baryonic content. Building on this insight, we present the first analytic and physically interpretable cosmological tracer that links the matter density parameter, $\Omega_m$, directly to intrinsic galaxy-scale observables, demonstrating that cosmological information can be extracted from individual galaxies. Using symbolic regression applied to state-of-the-art hydrodynamical simulations from the CAMELS project, we identify a compact functional form that robustly recovers $\Omega_m$ across multiple simulation suites (IllustrisTNG, ASTRID, SIMBA, and Swift-EAGLE), requiring only modest recalibration of a small number of coefficients. The resulting expression admits a transparent physical interpretation in terms of baryonic retention and enrichment efficiency regulated by gravitational potential depth, providing a clear explanation for why $\Omega_m$ is locally encoded in galaxy properties. Our work establishes a direct, interpretable bridge between small-scale galaxy physics and large-scale cosmology, opening a complementary pathway to cosmological inference that bypasses traditional clustering-based statistics and enables new synergies between galaxy formation theory and precision cosmology.
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All authors Kito Liao, Francisco Villaescusa-Navarro, Romain Teyssier, Natalí S. M. de Santi

Cosmology and Nongalactic Astrophysics

Gravitational Wave Informed Inference of 21-cm Global Signal Parameters

Avinash Tiwari, Sajad A. Bhat, Tirthankar Roy Choudhury et al. (+3 more)

Understanding how and when the first stars and galaxies formed remains one of the central challenges in modern cosmology. These structures emerged during the transition from the Dark Ages to the Cosmic Dawn, a period that remains observationally unconstrained despite strong theoretical progress. During this epoch, neutral hydrogen absorbed a fraction of cosmic microwave background photons through its 21-cm hyperfine transition, producing a 21-cm absorption signal whose evolution encodes the early Universe's thermal and ionization history. However, extracting the underlying astrophysical parameters from this signal is limited by severe parameter degeneracies, which cannot be resolved without independent observational probes. The next-generation gravitational wave (GW) detectors, such as Cosmic Explorer (CE), will observe binary black hole (BBH) mergers up to very large redshifts and hence will detect a fraction of them formed within the redshift range $\sim 13-25$. The merger rate of these BBHs will depend on the star formation rate density (SFRD) at these redshifts, together with the BBH formation efficiency and a time delay distribution. Therefore, the merger rate of these BBHs can work as a tracer of the SFRD in the redshift range $\sim 13-25$. In this Letter, we establish a novel multi-messenger framework and present a proof-of-principle concept of how the observations of BBH mergers form next-generation GW detectors can improve the inference of parameters generating the 21-cm cosmic hydrogen signal, and help break degeneracies between them.
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All authors Avinash Tiwari, Sajad A. Bhat, Tirthankar Roy Choudhury, Susmita Adhikari, Mukesh Kumar Singh, Shasvath J. Kapadia

High Energy Astrophysical Phenomena

A Multi-messenger Search for a Nearby Microquasar Contributor to the Cosmic Ray Knee

Lin Nie, Hua Yue, Yi-Qing Guo et al. (+1 more)

Recently, LHAASO has detected five microquasars with high confidence, which are associated with SS 433, V4641 Sgr, GRS 1915+105, MAXI J1820+070, and Cygnus X-1, respectively. Except for Cygnus X-1, the maximum energies of gamma-ray photons emitted from these sources all exceed 100 TeV, strongly suggesting that microquasars are capable of accelerating cosmic-ray particles to energies above the PeV range. This work investigates the origin of the cosmic-ray knee region based on gamma-ray observational data from the aforementioned sources, combined with cosmic-ray proton, helium, and all-particle energy spectra, as well as anisotropy observations. Calculations indicate that these known sources contribute negligibly to the cosmic-ray knee region. However, further joint analysis reveals that a single microquasar located in a region approximately on the 2.6 kiloparsec scale in the anti-Galactic center direction can reasonably reproduce the observed cosmic-ray proton, helium, and all-particle energy spectra, as well as anisotropy features detected near Earth. We propose that this region may host one or several unidentified microquasars or similar systems, whose accelerated cosmic rays could dominate the observational characteristics of the knee region.
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All authors Lin Nie, Hua Yue, Yi-Qing Guo, Si-Ming Liu

High Energy Astrophysical Phenomena

Two-component $\gamma$-Ray Structure from the CR Sources Within Dense Clouds

Lin Nie, Yi-Qing Guo and Si-Ming Liu

Recent observations have revealed that several cosmic ray (CR) sources themselves exhibit pronounced double power-law features in their radiation spectra. Combined with the phenomenon of two-component structure in the observed CR energy spectrum supported by multi-messenger data, this raises a fundamental question: can the two-component structure of the cosmic ray energy spectrum and the double power-law feature of the gamma-ray radiation energy spectrum from supernova remnants be understood within a unified picture? In this study, we propose a two-component model that incorporates the re-acceleration of background “sea" CR particles by astrophysical sources to systematically explain the formation of double power-law spectra within those sources. Our model successfully reproduces the gamma-ray observations of multiple CR sources. The results support that double power-law structures may be a generic feature of Galactic CR sources within crushed clouds. This work offers a new theoretical perspective on the origin and propagation of cosmic rays, and its predictions may be further tested with future observations of a larger sample of CR sources.
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Astrophysics of Galaxies

Properties of Galactic Outflows Driven by Starburst at Cosmic Noon: Insights from Hydrodynamical Simulations

Huan Chen, Weishan Zhu, Xue-Fu Li et al. (+3 more)

We investigate starburst-driven galactic outflows in low-mass galaxies ($9.0 < \log(M_*/M_\odot) < 10.0$) at cosmic noon using high-resolution 3D hydrodynamical simulations based on a framework that can reproduce the multiphase outflows in M82. The simulations produce starbursts lasting 20-30 Myr, with peak star formation rates of 2-68 M$_\odot \,\rm{yr}^{-1}$. Outflow properties vary strongly with time, radial distance to galaxy center, stellar mass, and gas fraction, exhibiting velocities of 50-1000 $\,\rm{km\,s}^{-1}$, mass outflow rates of 0.3-20 M$_\odot \,\rm{yr}^{-1}$, and mass loading factors, $\eta_\mathrm{M}$, of 0.24-6.26. The cool phase ($8000 < T \le 2 \times 10^4$ K) dominates the outflow, and properties of the cool and warm phases are broadly consistent with observations. At $M_*= 10^{9.5}\,M_\odot$, average $\eta_\mathrm{M}$ for the total, cool, and warm phases are $\sim$1.2, 0.75, and 0.25, respectively. The mass loading factor decreases with increasing galaxy stellar mass, but increases with star formation rate. Given strong temporal and spatial evolution, scaling slopes from limited samples should be treated with caution. Our total $\eta_\mathrm{M}$ values are higher than FIRE-2 by 0.06 dex but lower than EAGLE and TNG50 by 0.50 and 0.84 dex. Accounting for methodological differences in outflow measurement reduces these gaps to 0.2-0.4 dex, suggesting that part of the discrepancy between observations and simulations reported in the literature may arise from inconsistent definitions and measurement methods, though differences in individual phases persist. Larger observational and simulation samples, together with consistent methods for measuring outflow properties, are required to draw robust conclusions about the scaling relations of galactic outflows.
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All authors Huan Chen, Weishan Zhu, Xue-Fu Li, Tian-Rui Wang, Antonios Katsianis, Long-Long Feng

Cosmology and Nongalactic Astrophysics

Prospective bounds on f(Q) gravity with pulsar timing arrays

Mohammadreza Davari and Alireza Allahyari

Pulsar timing arrays (PTAs) have recently provided compelling evidence for a stochastic gravitational wave background (SGWB) in the nanohertz frequency band, offering a unique window into fundamental physics. Here, we explore implications for symmetric teleparallel $f(Q)$ gravity, a theory in which deviations from General Relativity (GR) arise through the non-metricity scalar $f(Q)$. Crucially, tensor modes propagate at the speed of light in this framework. However, their amplitude undergoes a modified damping during their evolution. We adopt a model-independent parameterization and derive an analytic approximation to the tensor mode transfer function to obtain the spectral energy density of primordial inflationary gravitational waves. Comparison with the NANOGrav 15-year and IPTA second data releases show that the inferred damping parameter $n$ remains consistent with GR, yet allows small deviations that could be observable. We then conduct a Fisher information matrix forecasts which demonstrate that the Square Kilometre Array (SKA) observatory will improve these constraints by several orders of magnitude, offering the potential to distinguish $f(Q)$ gravity from GR with high precision. These results highlight PTAs as powerful probes of non-metricity-based modifications to gravity.
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Earth and Planetary Astrophysics

A tension between dust and gas radii: the role of substructures and external photoevaporation in protoplanetary disks

Luca Delussu, Rossella Anania, Tilman Birnstiel et al. (+5 more)

Protoplanetary disk substructures are thought to play a crucial role in disk evolution and planet formation. Population studies of disks large-sample size surveys show that substructures, and their rapid formation, are needed to reproduce the observed spectral indices. Moreover, they enable the simultaneous reproduction of the observed spectral index and size-luminosity distributions. This study aims to investigate the necessity of substructures and predict their characteristics to reproduce gas-to-dust size ratios observed in the Lupus star-forming region. We performed a population synthesis study of gas and dust evolution in disks using a two-population model (two-pop-py) and the DustPy code. We considered the effects of viscous evolution, dust growth, fragmentation, transport, and external photoevaporation. The simulated population distributions were obtained by post-processing the resulting disk profiles of surface density, maximum grain size, and disk temperature. Although substructures help reduce the discrepancy between simulated and observed disk gas-to-dust size ratios; even when accounting for external photoevaporation, they do not fully resolve it. Only specific initial conditions in disks undergoing viscous evolution with external photoevaporation can reproduce the observations, highlighting a fine-tuning problem. While substructured disks reproduce dust size and spectral index, they tend to overestimate gas radii. The results ultimately highlight the main challenge of simultaneously reproducing gas and dust sizes. One possible explanation is that the outermost substructure is linked to the disk truncation radius, which determines the gas radius, or that substructures are frequent enough to always be near the gas outer radius.
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All authors Luca Delussu, Rossella Anania, Tilman Birnstiel, Claudia Toci, Giovanni Rosotti, Sebastian Markus Stammler, Tommy Chi Ho Lau, Anna Miotello

Instrumentation and Methods for Astrophysics

Scintillation muon telescope module with fiber-optic light collection

Belov S.M. and Yanke V.G

A scintillation muon telescope module with fiber-optic light collection using silicon photomultipliers was developed, tested, and installed for continuous monitoring to study cosmic ray variations. The aim of this study was to create a scintillation muon telescope module, continuously monitor the muon component in test mode, and study the long-term stability of the detector parameters. Methods for processing the obtained data were developed. To assess the stability of the module parameters, an internal control technique was used, involving data from other detectors. The results of testing and long-term continuous monitoring showed that the stability of the developed muon detector is better than 0.1%/year, without the need for its operation in a thermostatic chamber. The study concludes that ease of operation, cost, compactness, low power consumption and stability are factors that determine the advantages of the developed module, which is an essential element for constructing a multidirectional muon telescope.
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High Energy Astrophysical Phenomena

Astrophysical positronium and Dicke superradiance

Abdaljalel E. Alizzi and Zurab K. Silagadze

Dicke superradiance is a fascinating phenomenon in which a large number of atoms cooperate to produce a brief and very intense burst of spontaneous emission. This phenomenon has been well studied in the laboratory, but its astrophysical aspects have only recently attracted the attention of a small number of researchers. Since the phenomenon of Dicke superradiance is relatively little known to the wider astrophysical community, we provide a fairly detailed review of its elementary theory in the appendix and speculate on the significance of superradiance for astrophysical hydrogen and positronium, given the abundant formation of the latter near the galactic center.
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Instrumentation and Methods for Astrophysics

Toward Vision-Language Assistants for Radio Astronomical Source Analysis

S. Riggi

Vision-language models (VLMs) have recently shown promise in general-purpose reasoning tasks, yet their applicability to domain-specific scientific workflows remains largely unexplored. In this work, we evaluated a series of open-weight and commercial VLMs on six tasks relevant to radio astronomy, such as source morphology classification. We also introduced radio-llava, a fine-tuned multimodal assistant built on the LLaVA architecture and adapted for the radio domain through instruction fine-tuning. In zero-shot mode, commercial models like GPT-4.1 outperform open-weight VLMs on most radio benchmarks. However, radio-llava significantly improves upon both base LLaVA and commercial models across nearly all tasks. Despite these gains, specialized vision-only models still deliver substantially better performance across the board. Additionally, we observed that fine-tuning introduces catastrophic forgetting on general multimodal tasks, with performance drops up to 40% that can be partly mitigated with a more diverse training dataset or shallow fine-tuning.
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Solar and Stellar Astrophysics

SXP 31.0 – the 2025 near-Eddington double X-ray outburst after 26 years of quiescence

Malcolm J. Coe, Thomas M. Gaudin, Itumeleng M. Monageng et al. (+5 more)

SXP 31.0 is an X-ray source in the Small Magellanic Cloud (SMC) that was first identified as a Be X-ray Binary (BeXRB) system when it went into X-ray outbusrst in 1998. It is now known to consist of an OBe main sequence star and a neutron star with a spin period of 31s. In 2025 a new X-ray outburst phase began with the source exhibiting a luminosities approaching the Eddington limit of 10^38 erg/s. Unusually, H-alpha images show it has a surrounding halo whose nature has not been clear. In this paper, we report new observations of this halo, including the first multi-fibre Integrated Flux Unit (IFU) observations, which identify this emission as probably a coincidental HII region. The X-ray, UV & optical data cover a period of ~200d and reveal that the source underwent two bright, back-to-back, Type II outbursts in 2025 - a rare occurrence for any BeXRB system.
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All authors Malcolm J. Coe, Thomas M. Gaudin, Itumeleng M. Monageng, Jamie A. Kennea, David A. H. Buckley, Andrzej Udalski, Phil A. Evans, Sabyasachi Chattopadhyay