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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 25 June

Cosmology and Nongalactic Astrophysics

Quintom Model Perturbations

L. W. K. Goh and A. N. Taylor

We build upon the work of Goh and Taylor 2025, in which we proposed a two scalar field quintom framework capable of naturally realising a phantom-to-quintessence transition in the dark energy equation of state. In this work, we derive the linear perturbation equations of our model and investigate its implications for large scale structure formation. We show that the quintom model is able to reproduce the phenomenological features of a w0waCDM cosmology with phantom-to-quintessence crossing, including suppressions in the matter power spectrum and enhancements to the late-time Integrated Sachs-Wolfe effect. We then perform a Bayesian analysis of the quintom framework with BAO, CMB and Type 1a supernovae data, finding that it is mildly favoured over the standard w0waCDM parametrisation, while successfully reproducing physical trends observed in the data. We further examine the parameter degeneracies inherent to the model and discuss prospective observational strategies for distinguishing quintom cosmologies from conventional dynamical dark energy models given current and future data precision.
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High Energy Astrophysical Phenomena

Optical observations of candidate host galaxies of eight fast X-ray transients

Agnes P. C. van Hoof, Peter G. Jonker, Lieke Tommel et al. (+15 more)

Fast X-ray transients (FXTs) are extragalactic flashes of X-rays with a typical duration of minutes to hours for which a variety of origins has been proposed and observed. To decipher the origin of FXTs, particularly those lacking multi-wavelength counterparts, we aim to understand their energetics and environments. We present deep optical ground-based observations of the positions of eight FXTs in order to try and identify and characterize candidate host galaxies. We use their properties to discriminate between possible progenitor scenarios. We identify candidate host galaxies for Swift~J050400.2+673405, XRT140507, XRT040610, XRT151121, XRT191127 and EP240708a. For each candidate, we infer the spectroscopic or photometric redshift, stellar mass, star formation rate, metallicity and stellar population age by fitting our data with the spectral energy distribution fitting code BAGPIPES. We re-identify XRT191223 as a Galactic stellar flare. For several FXTs, there are multiple candidate host galaxies, which complicates deriving constraints on the origin of the FXT. Assuming association with (one of) those candidates, all are consistent with a (non-)relativistic white dwarf - intermediate mass black hole tidal disruption event (WD-IMBH TDE) and a binary neutron star (BNS) merger. Two are consistent with a supernova shock breakout and only EP240708a with cocoon emission from a long gamma-ray burst. We also discuss the possibility that the host galaxies remain undetected in our observations. We conclude that FXTs detected by Chandra and XMM-Newton are likely to arise from a variety of origins, and we discuss that part of this population differs from FXTs detected by Einstein Probe many of which appear consistent with a collapsar scenario.
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All authors Agnes P. C. van Hoof, Peter G. Jonker, Lieke Tommel, Jonathan A. Quirola-Vásquez, Daniel Mata Sánchez, Joyce N. D. van Dalen, Andrew J. Levan, Morgan Fraser, Ann Zabludoff, Manuel A. P. Torres, Javi Sánchez-Sierras, Antonio Martin-Carrillo, Thomas Wevers, Marco Berton, Minghao Yue, Vik S. Dhillon, Franz E. Bauer, Stuart P. Littlefair

High Energy Astrophysical Phenomena

Gamma-ray Bursts and Kilonovae from Gravitational Wave Events

Alberto Colombo, Marcello Giroletti, Susanna D. Vergani et al. (+1 more)

The detection of gravitational waves (GWs) from binary black holes in 2015 and the joint GW-electromagnetic (EM) observation of the binary neutron star merger GW170817 set a milestone in the multimessenger era in astrophysics. After four observing runs by the LIGO, Virgo, and KAGRA interferometers, a new cycle is planned for 2028, paving the way for next-generation detectors in the 2030s – such as the Einstein Telescope, Cosmic Explorer, and LISA. The prospects for joint GW-EM studies, including kilonova searches in wide optical surveys, are vast but demanding. In the radio domain, connected interferometers and VLBI arrays have already proven essential in constraining the ejecta properties of GW170817. Radio emission from gamma-ray burst (GRB) afterglows, whether on- or off-axis, remains detectable for very long time, making radio observations the most effective method for identifying and tracking GW merger counterparts. These observations enable precise characterization of system evolution, detailed probing of GRB jet structures, and possible detection of misaligned jets once their velocity becomes non-relativistic. Even in its initial configuration (AA*), the SKAO will provide the sensitivity and field of view needed to complement GW counterpart searches during O5 and beyond, offering unmatched capabilities for long-term monitoring. Furthermore, independent of the GW detections, SKAO will enable population studies of the properties of both long (produced by the collapse of massive stars) and short (produced by the merger of neutron stars) GRBs, of their jets and of their environment. We present an overview of this evolving observational landscape and of the key scientific questions SKAO will address.
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All authors Alberto Colombo, Marcello Giroletti, Susanna D. Vergani, Lauren Rhodes

Astrophysics of Galaxies

Unveiling the roles of thermal and nonthermal processes in the ISM & IGM structure formation and evolution of galaxies with SKAO

Fatemeh S. Tabatabaei, Masoumeh Ghasemi-Nodehi, Mark T. Sargent et al. (+10 more)

Investigating the thermal and nonthermal processes in the interstellar medium (ISM) and intergalactic medium (IGM) is vital to understanding the evolution of galaxies over cosmic time. Resolved observations with SKA pathfinders show that the nonthermal processes, in which magnetic fields and cosmic rays are involved, can decelerate the formation of massive stars in strongly magnetized regions in nearby galaxies. They can also contribute to the onset of winds and outflows in galaxies. The effects of these processes are stronger at higher redshifts as a result of star formation activities. The SKA Observatory will allow a major breakthrough by mapping the thermal and nonthermal processes in distant universe galaxies, shedding light on the role of the ISM and IGM in the evolution of galaxies. We demonstrate this by simulating the radio continuum and HI emission from local galaxies back to high redshifts. Our simulations show that the AA4 surveys will make it possible to trace the thermal and nonthermal processes of the ISM in galaxies that are analogs to M51 and NGC6946, traced in continuum beyond cosmic noon (z=2-3) and the gas content traced by HI beyond z=1. Both simulations and precursor observations indicate the importance of nonthermal feedback at cosmic noon.
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All authors Fatemeh S. Tabatabaei, Masoumeh Ghasemi-Nodehi, Mark T. Sargent, Mahdiyar Mousavi-Sadr, Maryam Khademi, Eva Schinnerer, Eric J. Murphy, Elizabeth A. K. Adams, Isabella Prandoni, Cathy Horellou, Volker Heesen, Javier Moldon, Ilsang Yoon

Instrumentation and Methods for Astrophysics

SMR: Scheduler with Multi-Channel Map-Encoded Reinforcement Learning for Radio Telescopes

Zhenyang Huang, Na Wang, Zhiyong Liu et al. (+1 more)

Observation scheduling for large single-dish radio telescopes is a multi-objective optimization problem: schedulers must maximize on-source scientific return under strict mechanical and environmental constraints. Previous dynamic scheduling relies on expert-designed heuristics, while existing reinforcement-learning (RL) approaches often struggle with variable-length target lists and lack an intrinsic representation of sky geometry. We present SMR (Scheduler with Map-encoded Reinforcement Learning), which projects discrete targets onto an azimuth–elevation (Az–El) grid in the local horizon frame. The resulting aligned multi-channel sky maps encode target attributes together with direction-dependent cues such as satellite-interference risk and elevation-dependent receiver gain. This representation provides an explicit spatial inductive bias and enables SMR to learn directly from the sky state. Simulations based on real catalogs and site parameters show that, compared with a tuned look-ahead greedy baseline, SMR achieves about a 10% relative improvement in time utilization by learning non-myopic scheduling strategies. In the full three-channel setting, SMR further achieves joint trade-off among efficiency, interference avoidance, and observation quality, with up to 17% higher LIER and 54% higher HGOR relative to an MLP baseline while maintaining higher utilization across both 12 h and 24 h horizons. Overall, SMR provides a simple and extensible way for data-driven single-dish scheduling.
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All authors Zhenyang Huang, Na Wang, Zhiyong Liu, Chuhao Gao

Astrophysics of Galaxies

HI Galaxy Science with the SKA

Jing Wang, D.J. Pisano, Sarah Blyth et al. (+9 more)

This chapter introduces the contributions of the HI galaxy science in this volume reviewing the latest developments and urgent questions in HI galaxy science, providing guiding principles for a layered set of future key science projects. The key science will include: a complete censuses of HI morphologies and kinematics at sub-kpc and 1 km/s resolution within and around galaxies in the nearby Universe; a measurement of the cosmic HI mass density and HI mass function evolution at least up to z~1; an improved understanding of the Universe at z>1, particularly the balance between cold molecular and cool atomic gas. We also provide a view of the synergistic multi-wavelength surveys available in 2028+ in the southern hemisphere. This effort will improve our understanding of the baryon cycle across a significant fraction of the cosmic history, including the processes of gas accretion, consumption and removal as well as AGN and star formation feedback. Based on these science goals, the earlier proposed three-tiered survey strategy remains, but survey parameters and predictions are adjusted according to AA* and AA4 developments. This chapter is an update of the earlier "Advancing Astrophysics with the Square Kilometre Array" chapter 'HI Science with the SKA' by Staveley-Smith & Oosterloo.
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All authors Jing Wang, D.J. Pisano, Sarah Blyth, Neeraj Gupta, Barbara Catinella, Lister Staveley-Smith, Paolo Serra, Elizabeth A. K. Adams, W.J.G. de Blok, Martin Meyer, Lourdes Verdes-Montenegro, Tom Oosterloo

High Energy Astrophysical Phenomena

Exploring Tidal Disruption Events with SKA and VLBI: Unveiling the Mystery of Black Hole Feeding and Outflows

Xinwen Shu, Guobin Mou, Tao An et al. (+8 more)

Tidal disruption events (TDEs) probe the birth and evolution of black hole accretion flows and jets on human timescales. Radio emission traces shocks and outflows from thermal TDEs and powerful relativistic jets in the rare jetted class. SKA Mid, phased for VLBI and used together with global networks, will deliver milliarcsecond imaging, tens of microarcsecond astrometry, and microJy sensitivity, enabling: (i) proper motion measurements that discriminate off axis relativistic jets from subrelativistic winds; (ii) resolved morphologies and magnetic field diagnostics via polarimetry; and (iii) precise nuclear localization to distinguish SMBH vs. IMBH and to reveal recoiling or binary systems. SKA's wide frequency coverage (0.35 to 15.4 GHz) and 1h continuum sensitivities of 3 to 10 microJy per beam, together with multibeam tiedarray VLBI and a transient buffer for rapid triggers, are transformational. LSST, Einstein Probe, and SVOM will increase TDE alerts to hundreds per year, and late time radio flares appear common, ensuring rich SKA VLBI samples. We provide observing strategies, detection forecasts, and predictions, e.g., about 5 proper motion detections of jetted (or off axis) TDEs per year and routine core shift constraints at the microarcsecond level. This program will establish TDEs as laboratories for exploring jet launching, particle acceleration (including neutrinos), black hole accretion history and demographics, and properties of circumnuclear medium.
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All authors Xinwen Shu, Guobin Mou, Tao An, S. Komossa, Miguel Perez-Torres, Weihua Lei, Luming Sun, Ning Jiang, Tinggui Wang, Chichuan Jin, Jun Yang

Instrumentation and Methods for Astrophysics

How to access astronomical observation facilities ?

Michaël De Becker

Access to astronomical data is a central component of astrophysical research. The allocation of telescope time is organized on an international scale through a highly competitive process. Over the past decades, this framework has evolved toward an increasingly professionalized system, particularly in the context of calls for telescope time proposals issued by major agencies or organizations, where hundreds of projects may compete for selection. Preparing a telescope time proposal is a demanding task for which junior researchers are not always adequately prepared. Astrophysicists typically acquire this expertise through first-hand experience, either by submitting their first proposal or by participating as members of a proposing team. At the same time, competition for telescope time is intense, and the significant effort invested in proposal preparation is accompanied by a non-negligible risk of rejection. This paper aims to present the general framework governing telescope time applications for both ground-based and space-borne observatories, with particular emphasis on the preparation of telescope time proposals. It discusses a set of key guidelines, some mandatory and others advisory, intended to help proposers navigate the application process more effectively, avoid common pitfalls and procedural missteps, and ultimately reduce the likelihood of preventable factors leading to a substantial decrease in the probability of selection.
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High Energy Astrophysical Phenomena

Broad-band Spectral Modeling of Large-Scale X-ray Jets in High-Redshift Quasars: An MHD-Informed Approach

Patryk Liniewicz, Łukasz Stawarz, C. C. Cheung et al. (+2 more)

We present a systematic spectral analysis of kiloparsec-scale jets in high-redshift quasars, modeling their radio-to-X-ray emission as synchrotron radiation and inverse-comptonization of CMB by relativistic electrons. In contrast to the homogeneous one-zone approximation commonly adopted in the literature, we describe the jet as a current-carrying, axially symmetric outflow with a purely toroidal magnetic field in magnetohydrostatic equilibrium and with radial velocity shear. In this framework, the pressure, magnetic-field, and bulk-velocity profiles are linked self-consistently, capturing the radial stratification of the emitting region without introducing additional free parameters. For any individual source, the model effectively retains only a small number of free parameters, including the total jet power, $L_{\rm j}$, and the on-axis bulk Lorentz factor, $\Gamma_0$. We consider two prescriptions for the radial distribution of the radiating electrons – proportional either to the gas pressure or to the rest-frame magnetic energy density – and two toroidal-field profiles, yielding four model variants. Applying the model to a sample of ten quasar jets at $z \geq 2.5$ with X-ray features resolved by Chandra, we perform Bayesian parameter inference and model comparison. The Bayesian evidence systematically favors electron distributions that follow the gas pressure rather than the magnetic energy density, while the data discriminate only weakly between the assumed field profiles. The inferred jet powers, reaching $L_{\rm j} \sim 10^{49}\,\mathrm{erg\,s^{-1}}$, are systematically larger than those obtained from one-zone models, and the corresponding global jet magnetization parameters are low. None of the derived quantities, including $\Gamma_0 \sim \mathcal{O}(10)$, shows a significant monotonic trend with redshift.
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All authors Patryk Liniewicz, Łukasz Stawarz, C. C. Cheung, Giulia Migliori, Aneta Siemiginowska

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

A geometric multimessenger consistency test of radiative and near-zone gravity with LISA and SKA

Bhooshan Gadre

Compact binary pulsars observed both through precision radio timing and low-frequency gravitational waves offer a direct way to compare the same binary geometry with two independent messengers. We propose a multimessenger consistency test based on the orbital inclination, measured from the Shapiro-delay shape parameter in radio timing and from the tensor polarization amplitude ratio in the gravitational-wave signal. Defining the common-epoch residual $\eps(t_0)=s_{\rm Shapiro}(t_0)-s_{\rm GW}(t_0)$, general relativity predicts $\eps=0$, while a nonzero value would indicate either an unmodeled systematic or a mismatch between the near-zone and radiative descriptions of gravity. We estimate the attainable precision on this quantity for representative LISA–SKA compact binary pulsars using a seven-parameter timing Fisher matrix and a sky-averaged LISA sensitivity curve including the Galactic foreground. We adopt a conservative radio baseline, $\sigma_{\rm TOA}=1\,\mu{\rm s}$ and $N_{\rm eff}=10^4$, intended to summarize radiometer noise, jitter, residual dispersion-measure and scattering effects, profile evolution, and cadence losses after wideband timing. For systems at $d=5\,{\rm kpc}$ observed for four years, we find $\sigma_\eps\simeq4\times10^{-3}$ for a favorable double neutron star and $\sigma_\eps\simeq9\times10^{-4}$ for a hypothetical pulsar–black-hole system. The former is the more robust astrophysical benchmark; the latter illustrates the reach if such a high-SNR chirping source is discovered. The useful cases remain limited mainly by gravitational-wave polarimetry, while radio timing supplies the near-zone reference measurement of the inclination. These results define a quantitative target for future joint Bayesian analyses of compact binary pulsars observed in both radio and gravitational waves.
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Instrumentation and Methods for Astrophysics

VLBI with SKAMPI, the SKA-Mid MPIfR dish demonstrator

Jompoj Wongphechauxsorn, Niclas Alexander Esser, Tobias Winchen et al. (+13 more)

The SKA-MPIfR telescope (SKAMPI) is a prototype SKA-Mid antenna located at the SKA site in the Karoo Desert, South Africa. It is funded by the Max Planck Society, through the Max Planck Institute for Radio Astronomy (MPIfR), and operated in collaboration with the South African Radio Astronomy Observatory (SARAO). The first fringe-finding experiments have been conducted with the European VLBI Network and the southern hemisphere Long Baseline Array, connecting SKAMPI with Europe and Australia. Here we present early SKAMPI VLBI mode results in S-Band, including successful fringe detections and evaluating the integration and imaging performances of SKAMPI in observations with the EVN, LBA, and VLBA.
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All authors Jompoj Wongphechauxsorn, Niclas Alexander Esser, Tobias Winchen, Jan Wagner, Uwe Bach, Hans-Rainer Klöckner, Michael Kramer, Gundolf Wieching, Ewan Barr, Jonathan Quick, Roger Deane, Cormac Reynolds, Phil Edwards, Chris Phillips, Matthias Kadler, Roopesh Ojha

High Energy Astrophysical Phenomena

Unraveling the mysteries of supernovae with SKA+VLBI

Tao An, Zhengwei Liu, Ailing Wang et al. (+6 more)

Supernovae (SNe) drive cosmic chemical enrichment and shape galactic feedback, yet the link between progenitors and explosion outcomes remains poorly constrained because the earliest phases are rarely resolved. Radio emission traces synchrotron radiation where the fastest ejecta interact with the circumstellar medium (CSM), providing a uniquely penetrating probe of these phases. SKA-Mid phased into global VLBI will move from simple detections to routine interferometric imaging of nearby extragalactic SNe. Sub-$\mu$Jy sensitivity and mas-scale SKA+VLBI imaging, complemented by visibility-domain model fitting for sub-beam radius measurements at 5-15 GHz will allow us to follow the expanding shocks of stripped-envelope SNe out to $\sim$25 Mpc, measure deceleration indices ($m$) and axial ratios to $\approx 5-10\%$, and directly test jet-assisted versus neutrino-driven explosion mechanisms. For interacting SNe (Type IIn/Ibn), SKA+VLBI will resolve clumpy and toroidal CSM on progenitor scales, constraining the timing and geometry of eruptive pre-explosion mass loss. Deep limits on Type Ia SNe will tightly restrict the allowed single-degenerate parameter space, while late-time imaging will search for nascent compact remnants and pulsar wind nebulae. In synergy with optical, X-ray and gravitational wave facilities, SKA+VLBI will turn nearby SNe into laboratories for time-resolved shock physics and progenitor mapping.
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All authors Tao An, Zhengwei Liu, Ailing Wang, Miguel Pérez-Torres, Javier Moldon, Liangduan Liu, Peter Lundqvist, Xuefei Chen, Xiangcun Meng

High Energy Astrophysical Phenomena

Transforming X-ray Binary Astrophysics with SKA+VLBI

Tao An, Ailing Wang, James C. A. Miller-Jones et al. (+6 more)

X-ray binaries (XRBs) are unique laboratories where accretion, jets, strong gravity and magnetic fields can be probed on humanly tractable timescales. The phased SKA-Mid operating as a single, ultra-sensitive Very Long Baseline Interferometry (VLBI) element will transform radio studies of XRBs primarily through its time-domain capabilities: substantially improved sensitivity on VLBI baselines that include SKA-Mid in Bands 2 and 5, together with connected-element SKA-Mid imaging extending down to 0.35–1 GHz (Band 1), microarcsecond-precision astrometry for bright systems, high-fidelity polarimetry for the most strongly polarized sources, and rapid target-of-opportunity response. In synergy with global VLBI networks, SKA+VLBI will track the evolution of compact ejecta and compact jets on astronomical unit (AU) scales, measure frequency-dependent core shifts to infer magnetic field strengths and gradients, resolve disk–jet coupling during state transitions in real time, and determine precise distances and natal kicks via parallaxes and proper motions. Joint campaigns with future X-ray and optical telescopes will enable strictly simultaneous, multi-band constraints on accretion–ejection physics and on jet composition. We outline a quantitative program for \aastar\ and AA4, including cadenced, multi-frequency VLBI “movies” of jets over the first days of outbursts, an XRB astrometric census, and a core-shift survey, and we provide representative detection rates, magnetic field measurements and distance accuracies. These outcomes will set the microphysical foundation for jet physics across the mass scale from stellar-mass black holes and neutron stars to active galactic nuclei, and will establish SKA+VLBI as the definitive facility for time-domain, high-resolution XRB astrophysics.
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All authors Tao An, Ailing Wang, James C. A. Miller-Jones, Valeriu Tudose, Pikky Atri, Lang Cui, Hua Feng, Benito Marcote, Sara E. Motta

Instrumentation and Methods for Astrophysics

Cascade adaptive optics with a second stage based on a Zernike wavefront sensor for exoplanet observations II. Validation in broadband light on the ESO/GHOST testbed

A. Rahim, M. N'Diaye, A. Vigan et al. (+10 more)

Current high-contrast facilities on the ground use extreme adaptive optics (XAO) systems to achieve contrasts down to $10^{-6}$ at 200\,mas for exoplanet observations. This performance is mainly limited by the XAO residuals due to the temporal errors in the XAO control loop. To overcome this issue, a promising solution consists in using cascade adaptive optics with a fast second stage. This approach was recently validated for a control loop based on a Zernike wavefront sensor (ZWFS) in monochromatic light. As wavefront sensors operate in broadband light to maximise photon sensitivity, this work aims to validate the ZWFS-based control loop in polychromatic light and assess its performance over a wide range of seeings, wind speeds, and stellar fluxes. Experiments were conducted on the ESO's GPU-based High-order adaptive OpticS Testbench (GHOST) testbed to probe our scheme in polychromatic light. Residual aberrations from a first-stage XAO system were simulated and our approach was evaluated in narrowband and broadband light through contrast in Lyot coronagraphic images. Closing the ZWFS-based control loop consistently improves contrast within its correction region in most tested conditions. After subtraction of quasi-static aberrations, our loop reaches a contrast gain up to one order of magnitude, independently of bandwidth and turbulence strength. The broadband and narrowband cases match in performance for bright sources, while narrowband remains slightly preferable for faint targets. These results demonstrate the feasibility of broadband ZWFS-based control loop and underline promising avenues with achromatic masks and an accurate calibration of quasi-static aberrations for future high-contrast imaging on Extremely Large Telescopes.
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All authors A. Rahim, M. N'Diaye, A. Vigan, M. Kasper, J. Nousiainen, B. Engler, K. Dohlen, S. Leveratto, J. Floriot, M. Marcos, C. Bailet, P. Bristow, E. S. Douglas

High Energy Astrophysical Phenomena

Supernova remnants in the new radio astronomy era

A. Ingallinera, M. Arias, G. Castelletti et al. (+25 more)

Supernova remnants (SNRs) are what is left after stellar explosions, when the stellar ejecta, the explosion shock and the circumstellar medium interact. Despite being among the first objects studied in radio astronomy, observational difficulties have so far prevented a definitive characterisation, which would help answer open questions related to these sources. It is debated which is the contribution of SNRs to Galactic cosmic rays, or how the interaction with the surrounding environments influences the particle energetics. The SKA precursors are providing valuable and unexpected discoveries on SNRs, thanks to their unique capabilities to probe spatial scales from a few arcseconds to a few degrees with a sensitivity of tens of microjansky. Accurate integrated flux density measurements and arcsecond-scale spectral-index maps are now possible for tens of SNRs, substantially expanding the small subset of remnants traditionally studied in great detail. SKA will markedly enhance current observations by providing: higher sensitivity, enabling the detection of fainter SNRs also in polarisation, revealing diffuse structures and the underlying magnetic field configuration; higher angular resolution, allowing detailed mapping of compact remnants and reducing depolarisation in fine structures, tracing filaments and shocks fronts; wider frequency coverage to probe unexplored spectral windows, where spectral turnovers and breaks or cut-off may occur, establishing a direct connection to X-ray and {\gamma}-ray emission that constrains the electron population, and enabling accurate modelling of the non-thermal emission across the electromagnetic spectrum; improved image fidelity for more reliable cross-matching with other wavelengths, leading to a better understanding of the SNR-interstellar medium interplay.
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All authors A. Ingallinera, M. Arias, G. Castelletti, C. Bordiu, F. Bufano, G. Cosentino, M. D. Filipović, D. Liu, S. Loru, S. Orlando, O. Petruk, Z. Smeaton, A. Traficante, C. Trigilio, G. Umana, G. Anderson, F. Bocchino, C. Buemi, F. Cavallaro, E. Egron, N. Hurley-Walker, R. Kothes, P. Leto, S. Mantovanini, M. Miceli, G. Morlino, A. Pellizoni, M. Sasaki

High Energy Astrophysical Phenomena

The Emerging Population of High-energy Emitting Radio Galaxies

G. Bruni, V. S. Paliya, D. J. Saikia et al. (+22 more)

High-energy emission from radio galaxies provides a unique laboratory to study the connection between accretion, jet formation, and particle acceleration in active galactic nuclei (AGN). The recent detection of $\gamma$-ray emission from misaligned radio galaxies - including Compact Symmetric Objects (CSOs), FR0, FRI/II, and even Giant Radio Galaxies (GRGs) - has shown that efficient particle acceleration is not limited to blazars, but occurs throughout the full radio-loud AGN population. This finding supports a unifying framework where leptonic synchrotron, synchrotron self-Compton (SSC), and external inverse-Compton (EIC) processes coexist across multiple spatial scales, from the inner jet and corona to the extended lobes, possibly with a hadronic contribution in dense environments. The Square Kilometre Array (SKA) will be pivotal in advancing this field. SKA1-Low will detect and characterize diffuse, low-surface-brightness emission tracing aged plasma and jet duty cycles. SKA1-Mid will enable high-resolution spectral and polarimetric studies of compact jets and nuclear regions, while SKA-VLBI will connect parsec- to kiloparsec-scale structures, identifying the exact sites of high-energy dissipation. In synergy with forthcoming high-energy missions such as NewAthena and CTAO, SKA will provide the first spatially resolved, multi-scale view of particle acceleration and energy release in misaligned AGN, unveiling the physical link between the central engine and its large-scale feedback on the host galaxy evolution.
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All authors G. Bruni, V. S. Paliya, D. J. Saikia, L. Bassani, R. D. Baldi, E. Bronzini, F. D'Ammando, S. del Palacio, M. Kadler, Y. Y. Kovalev, D. V. Lal, G. Migliori, B. Mingo, J. Moldon, L. Ostorero, F. Panessa, M. Persic, I. Prandoni, L. Ricci, T. Savolainen, F. Shankar, F. Tavecchio, E. Traianou, F. Ubertosi, T. Venturi

Instrumentation and Methods for Astrophysics · Cross-listed from physics.space-ph

Excursion-set structure factor of the auroral electric field

Magnus F Ivarsen, Kaili Song, Jean-Pierre St-Maurice et al. (+1 more)

We treat coherent radar echoes from aurorae as a finite point process and measure its structure factor $S(k)$ from pairwise echo separations. Backscatter requires electron drifts to exceed the ion-acoustic speed, making the echoes a threshold (excursion-set) sample of the ionospheric electric field, and $|S-1|$ is that field's spectrum, to leading order. We test this against in-situ observations: in co-moving frames, the radar spectrum is scale-free with a spectral index near -5/3, matching the in-situ indices. The auroral electric field is thus imaged by its excursion set, a point process of Farley-Buneman threshold exceedances.
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All authors Magnus F Ivarsen, Kaili Song, Jean-Pierre St-Maurice, Glenn C Hussey

Astrophysics of Galaxies

Theoretical determination of the binding energies of methanol and related species onto amorphous solid water ice

Aneesa Ahmad, Catherine Walsh, Stefan Vogt-Geisse et al. (+2 more)

The formation and survival of complex organic molecules (COMs) in cold interstellar environments depends on their interactions with icy dust grain surfaces. Methanol, a key COM detected in cold cores and protoplanetary disks, is believed to form on amorphous solid water (ASW) through surface reactions and reside there until it is desorbed into the gas phase. We present a theoretical study of the binding energies (BEs) of methanol and its photolysis-derived species on ASW clusters by means of dispersion-corrected density functional theory (DFT) using a refined protocol implemented in the Binding Energy Evaluation Platform (BEEP). Molecules capable of hydrogen bonding, such as H2O, CH3OH, HCOOH, and OH, exhibit high BEs and broad BE distributions that reflect the structural heterogeneity of the ASW surface. In contrast, weakly interacting volatiles including CO, CO2, CH4, and CH3 display narrower distributions dominated by dispersion interactions. Open-shell radicals such as CH2OH and OH bind more strongly than HCO and CH3 due to their ability to form directional hydrogen bonds. Incorporation of our BEs into an astrochemical model, in conjunction with a recalculation of the pre-exponential factor using transition state theory, demonstrates the sensitivity of model results to the method of calculation of the grain-surface reaction rates. The new approach generally predicts a higher abundance of radicals on the ice that are key reactants for the formation of COMs when surface diffusion is assumed to be efficient. These findings emphasize the importance of incorporating BEs that have been determined in a self-consistent manner into astrochemical models, and provide reliable theoretical benchmarks for species with limited experimental data.
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All authors Aneesa Ahmad, Catherine Walsh, Stefan Vogt-Geisse, Gabriela Silva-Vera, Felix Sainsbury-Martinez

Cosmology and Nongalactic Astrophysics

Distance-Ladder Measurements of the Hubble Constant: Recent Progress, Systematics, and Prospects

Xiaodian Chen and Shu Wang

The Hubble constant, \(H_0\), links the nearby distance scale to the present cosmic expansion rate. Local distance-ladder measurements now reach percent-level precision and remain more than \(5\sigma\) higher than the value inferred from cosmic microwave background (CMB) observations in base-\(\Lambda\)CDM, making the reliability of the local ladder a central issue in the Hubble tension. We describe the ladder as a covariance network connecting level-0 geometric anchors, level-1 stellar distance indicators, and level-2 Hubble-flow probes. The Cepheid–Type Ia supernova (SN Ia) route remains the most precise single local ladder, but independent indicators including the tip of the red giant branch (TRGB), J-region asymptotic giant branch (JAGB) stars, Mira variables, surface-brightness fluctuations (SBF), the Tully–Fisher relation, and Type II supernovae (SNe II) now test shared and method-specific systematics. In a compact seven-route covariance summary, combining the Cepheid–SN Ia route with three level-1 alternatives (TRGB, JAGB, and Mira) and three level-2 alternatives (SBF, Tully–Fisher, and SNe II) gives \(H_0=73.30\pm0.92~{\rm km~s^{-1}~Mpc^{-1}}\), still \(5.6\sigma\) above Planck base-\(\Lambda\)CDM. JWST has already tested Cepheid crowding and is making independent TRGB-based \(H_0\) measurements increasingly feasible. Over the next five years, a reliable one-percent local \(H_0\) requires larger calibrator samples, cross-validated level-1 zero points, explicit covariance propagation, and AI-assisted, reproducible, pre-specified selection criteria for distance-indicator measurements.
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Astrophysics of Galaxies

Probing outflow physics through CH$_3$CN and CH$_3$OH chemistry

L. Giani, D. Zaremba, M. De Simone et al. (+4 more)

Chemical correlations between molecules provide powerful diagnostics to probe the physical conditions of protostellar outflows. In particular, the relationship between methanol (CH$_3$OH) and methyl cyanide (CH$_3$CN) offers a promising tool to investigate the chemistry and irradiation environment of shocked gas. In this Letter, we use the CH$_3$OH/CH$_3$CN abundance ratio to constrain the physical properties of the outflow driven by the Class 0 protostar S68N using ALMA Band 3 and Band 6 observations. Assuming local thermodynamic equilibrium (LTE), we derive excitation temperatures of 50-60 K and column densities of 2-3$\times$10$^{13}$ cm$^{-2}$ for CH$_3$CN and 3-5$\times$10$^{15}$ cm$^{-2}$ for CH$_3$OH. The resulting CH$_3$OH/CH$_3$CN abundance ratio is nearly constant along the outflow, with values of $\sim$100-200, similar to those found in other protostellar environments. Using an up-to-date astrochemical model, we test whether gas-phase formation of CH$_3$CN can account for the observed ratios. We find that they are reproduced only by assuming enhanced cosmic-ray ionization rates $\zeta_{\rm CR}$ up to $\sim$10$^{-14}$ s$^{-1}$. These results suggest that the CH$_3$OH-CH$_3$CN correlation can be used as a probe of the irradiation conditions in protostellar outflows. Further studies are required to explore the possible contribution of grain-surface formation of CH$_3$CN which could lead to a lower $\zeta_{\rm CR}$ and to extend the analysis to a larger sample of sources.
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All authors L. Giani, D. Zaremba, M. De Simone, L. Tychoniec, L. Podio, C. Codella, A. Somigliana

Cosmology and Nongalactic Astrophysics

Probing inflationary particle production with the CMB power spectrum

Hidde T. Jense, Luca H. Abu El-Haj, J. Colin Hill et al. (+1 more)

Particle production is common to many microphysical models of inflation and can imprint observable features in the cosmic microwave background (CMB) anisotropies. We consider a scenario in which the inflaton couples to an extremely massive field ($m_\chi \gtrsim \mathcal{O}(100 H_I)$, where $H_I$ is the inflationary Hubble scale). In this model, particle production happens in a burst at a characteristic conformal time, $\eta_*$, which sources localized features in the CMB. In this paper, we compute the full temperature and polarization two-point functions for this model. We then search for these features in CMB power spectrum data from Planck and the Atacama Cosmology Telescope (ACT), with the latter allowing access to features on smaller angular scales. In the joint analysis of Planck and ACT data, we find a mild $\sim 2 \sigma$ hint for a signal induced by this inflationary model on scales $3 \,\, \text{Mpc}\leq\eta_*\leq 10 \,\, \text{Mpc}$, though this hint is not present at a statistically significant level in either dataset when analyzed individually. Using a Fisher forecast, we find that these features should be observable at the $3-5\sigma$ level for a Simons Observatory-like experiment, if they are indeed real. We also compare our power-spectrum-based constraints to previous matched-filter-based bounds on this model. For sufficiently light particles ($m_\chi \lesssim 200 H_I$), the power spectrum yields tighter constraints by more than an order of magnitude, but in the higher-mass regime where particle production is rare, the matched-filter approach provides stronger bounds.
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All authors Hidde T. Jense, Luca H. Abu El-Haj, J. Colin Hill, Oliver H. E. Philcox

Instrumentation and Methods for Astrophysics

Characterizing robotic positioners under the influence of changing gravity vectors for future spectroscopic surveys

Johannes Wüthrich, Guandi Zhao, Banan Yamani et al. (+5 more)

Future (Stage V) spectroscopic surveys intend to accurately map billions of galaxies. To accomplish this goal, these surveys will employ highly multiplexed focal planes composed of robotic fiber positioners to accurately place individual optical fibers on targets of interest. The ambitious science objectives place stringent requirements on the mechanical performance of these positioners. Experience from previous surveys has shown that testing positioners under conditions closely resembling those on the telescope is of utmost importance during the prototyping and quality assurance phases of construction. We present an automated telescope simulator test stand that characterizes the performance of these positioners at different orientations, reproducing the changing gravity vectors encountered during telescope operations. The test stand aims to verify position stability down to 1 um, focus stability down to 5 um, as well as tilt variations lower than 0.4 deg. We discuss the design of our setup, along with early characterization of image quality due to turbulence and the compensation of the enclosure deformation via calibration using fixed spots. Finally, we present initial results of positioning stability tests using a prototype module built by Orbray Co., Ltd. This test setup fulfills an important need for integrated testing of advanced focal plane prototypes under conditions similar to on-telescope conditions.
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All authors Johannes Wüthrich, Guandi Zhao, Banan Yamani, Léonard Lebrun, Sean MacBride, Andrin Fazan, Felipe Andrade-Oliveira, Marcelle Soares-Santos

Solar and Stellar Astrophysics

Investigating the System Configuration of Kepler-451 through Orbital Period Variations: Dynamical and Magnetic Interpretations

Huseyin Er, Aykut Ozdonmez, M. Emir Kenger et al. (+5 more)

We present an analysis of eclipse timing variations in Kepler-451 using data spanning 2004-2024 from both ground- and space-based observations. Using two datasets, DS-A and DS-B, we constructed updated O-C diagrams. By modeling both datasets with various LTT configurations, we tested for the presence of circumbinary companions. For DS-A, the two-companion model (LTT34) provides the best fit with RMS = 3.23 s and chi^2_nu = 1.23, while inclusion a fifth body (LTT345) does not improve the fit (RMS = 3.24 s, chi^2_nu = 1.28). For DS-B, the three-companion model (LTT345) yields the best fit (RMS = 2.31 s, chi^2_nu = 1.01), although the semi-amplitude of the inner companion (1.34 s) is smaller than the systematic error (1.81 s), suggesting that it may originate from observational or calibration systematics. Applegate-mechanism tests indicate that most signals exceed the available energy budget, while the outer LTT terms in both datasets remain consistent with the Standard model and may have a magnetic origin. Removing these magnetic terms yields dynamically stable configurations for at least 10^7 yr. These findings support the presence of a second-generation circumbinary planet at 3.4 AU around Kepler-451, while the origin of the remaining LTT signals remains uncertain.
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All authors Huseyin Er, Aykut Ozdonmez, M. Emir Kenger, B. Batuhan Gurbulak, Ilham Nasiroglu, Murat Tekkesinoglu, Ergun Ege, Nazli Karaman

Astrophysics of Galaxies

Feeding and Feedback in Dwarf Galaxies (FeeD) – I. Evidence of nuclear ultra-fast and galaxy-scale outflows in the dwarf galaxy Arp 151

Santanu Mondal, Ankit Patel, Mar Mezcua et al. (+5 more)

Feeding and feedback regulated by supermassive black holes (SMBHs) play a central role in galaxy growth and evolution, yet these processes remain poorly understood in low-mass galaxies. In particular, the presence, properties, and role of ultra-fast nuclear outflows (UFOs) in low-mass galaxy systems are largely unexplored. We analyze available NuSTAR X-ray observations of Arp 151 and find a possible evidence ($\sim 2\sigma$ confidence) for a fast outflow with a velocity of $\sim0.18c$ from the central BH. Furthermore, we have also detected an optical galaxy-scale outflow in MaNGA Integral Field Unit data. The estimated nuclear and galaxy-scale mass outflow rates are $\sim0.015$ $M_\odot$/yr from NuSTAR and $\sim0.43$ $M_\odot$/yr from MaNGA, respectively. Our estimates suggest that such outflows may significantly regulate the feedback process in the galaxy. Comparing the kinetics of the UFO and the galaxy-scale outflow indicates that they are in the momentum-conserving phase. This tentative detection implies that dwarf galaxies are also able to generate UFOs, which so far have been detected in massive galaxies. Thus, the AGN feedback may also be important for the evolution of the dwarf galaxies.
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All authors Santanu Mondal, Ankit Patel, Mar Mezcua, Ravi Joshi, Yerong Xu, K. Aditya, Smitha Subramanian, Victor Rodriguez Morales

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Stochastic gravitational wave spectrum from cosmic string emitting gauge bosons and Majorana fermions

Nobuchika Okada and Osamu Seto

The effect of particle radiation on the spectrum of the stochastic gravitational wave background (SGWB) from cosmic strings is studied. We consider cosmic strings in an Abelian-Higgs model coupling with Majorana fermion whose mass is generated by the Higgs field, motivated by a gauged $U(1)_{B-L}$ model, in which the Majorana fermions are identified with right-handed neutrinos. Taking the energy loss by particle radiation into account, we evaluate the resultant SGWB spectrum and demonstrate the emergence of very high frequency cutoff due to the particle radiation.
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Astrophysics of Galaxies

Validating the ICCF-Cut Method with Simultaneous Photometric and Spectroscopic H$\alpha$ Reverberation Mapping of NGC 4151 and UGC 3374

Chi-Zhuo Wang, Hai-Cheng Feng, Sha-Sha Li et al. (+2 more)

Photometric reverberation mapping (RM) provides an efficient alternative to spectroscopic RM for probing the broad-line region (BLR) sizes in AGNs. In our previous work, we proposed the ICCF-Cut method, which extracts H$\alpha$ emission-line variability from broadband photometric light curves and measures the lags to estimate the BLR sizes. To further assess the reliability of this method, we conduct simultaneous photometric and spectroscopic monitoring of two nearby Seyfert galaxies, NGC 4151 and UGC 3374, over multiple observing seasons using the Lijiang 2.4 m telescope. By directly comparing the photometric and spectroscopic RM results in each season, we find that the extracted H$\alpha$ light curves using the ICCF-Cut method closely resemble those derived from spectroscopy. The photometric H$\alpha$ lags are also generally consistent with the spectroscopic H$\alpha$ lags within the uncertainties. For several seasons where the photometric H$\alpha$ lags are slightly underestimated, we find that the discrepancy may be caused by residual He\,i contamination in the extracted H$\alpha$ light curves. After correcting for this contamination, the photometric lag measurements become more consistent with the spectroscopic results. We further explore the performance of the ICCF-Cut method using the simulated light curves with different filter bandwidths. For our observational and simulated cases, the method can successfully recover the emission-line variability and lag measurements broadly consistent with the spectroscopic results. This provides further support for the applicability of the ICCF-Cut method in photometric RM.
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All authors Chi-Zhuo Wang, Hai-Cheng Feng, Sha-Sha Li, Xue-Bing Wu, Qinchun Ma

Astrophysics of Galaxies

Semi-empirical Predictions for Ultra-deep Radio Counts of Star-forming Galaxies with the SKAO

M. Giulietti, I. Prandoni, L. Bisigello et al. (+4 more)

Star-forming galaxies (SFGs) dominate the faint radio sky at flux densities below 0.1 mJy. Identifying these systems through a multiwavelength approach is essential to tracing the cosmic history of star formation. Upcoming surveys with the Square Kilometre Array Observatory (SKAO) in its AA4 configuration for the Mid array will probe these faint populations, offering unprecedented insights into the star formation activity of galaxies across cosmic time. Semi-empirical models, built on minimal assumptions and empirical galaxy relations, provide an efficient framework to study galaxy evolution using recent radio and optical/near-infrared (NIR) data. We developed SEMPER (Semi-EMPirical model for Extragalactic Radio emission) to predict the radio luminosity functions and number counts of SFGs. SEMPER combines redshift-dependent stellar mass functions from deep NIR surveys with empirical relations such as the galaxy main sequence and the IR/radio correlation, to characterise the radio properties of massive, high-redshift galaxies. The model shows excellent agreement with recent deep radio observations and naturally predicts a substantial population of massive, dust-obscured galaxies already in place at early epochs. In this chapter, we extend the SEMPER framework to SKA surveys by including an evolving starburst fraction and computing differential number counts at 1.4 GHz for both lensed and unlensed SFGs. Furthermore, we predict the cosmic star formation rate density (SFRD) traced by radio-emitting galaxies up to $z\approx10$. Our results show that SKA surveys will probe the faintest flux-density regimes, dominated by galaxies powered by star formation, and that <20 hours of SKA-Mid Band 2 observations will recover at least $\approx$20% of the total SFRD predicted by SEMPER, including contributions from optically/NIR-dark systems up to $z\approx 6$.
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All authors M. Giulietti, I. Prandoni, L. Bisigello, M. Bondi, M. Massardi, M. Bonato, A. Lapi

Astrophysics of Galaxies

NO molecule in massive star forming regions

Shaomin Su, Junzhi Wang, Rui Luo et al. (+7 more)

Context. Among diatomic molecules composed of the abundant elements C, N and O, NO has been detected far less than the well studied CN and CO, making it a crucial yet under-observed component in nitrogen-containing chemical networks. NO was thought to serve as a potential tracer of shocks, as evidenced with orders abundance enhancements reported in literature. Aims. Large-sample observations for NO molecule in widespread interstellar environments are needed to confirm if the enhancement of NO is due to shock chemistry or not. Methods. Single-point survey for NO lines around 150 GHz was carried out by Arizona Radio Observatory 12-meter telescope towards a sample of 36 massive star forming regions containing SiO emission, which include three evolutionary stages: 4 IRDCs, 6 protostars and 26 H II regions. Results. The NO emission was detected in 28 sources with a detection rate of 78%. Beam-averaged NO column densities and abundances relative to H2 were derived from integrated intensities of two main hyperfine lines. Correlations between NO and SiO in integrated intensity and relative abundance are similar to the corresponding correlations of c-C3H2, indicating that NO enrichment may not significantly involve pronounced shock activities, which coincides with the trend in line widths: NO is close to c-C3H2, both smaller than H2CO and far smaller than SiO. Conclusions. Observational evidence does not strongly support significant NO enhancement by shock chemistry in the observed sources, indicating that the formation of NO does not necessarily require shocks.
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All authors Shaomin Su, Junzhi Wang, Rui Luo, Yani Xu, Fu Mo, Yijia Liu, Chang Ruan, Yingxue Kang, Yuqiang Li, Siqi Zheng

Astrophysics of Galaxies

SKA VLBI survey of the Southern sky for astrometry, geodesy, and astrophysics

M. H. Xu, L. Y. Petrov and Y. Y. Kovalev

The development of SKA will open the opportunity to run dedicated VLBI surveys of the Southern sky and observe sources not visible at radio telescopes located in the Northern hemisphere. These surveys will allow for doing geodesy with a Southern hemisphere-centered network, increase the density of compact radio sources that can be used as calibrators, further extend the celestial reference frame to deep south, and facilitate high-precision differential astrometry for a wide range of applications. Achieving a deep completeness level and determining the parsec-scale properties of extragalactic radio sources is crucial for multi-wavelength and multi-messenger astrophysics. This includes supporting Cherenkov and neutrino telescope science cases, as well as joint VLBI-Gaia studies of active galaxies.
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Astrophysics of Galaxies

Extended Structure in E+A Galaxies Via Image Stacking

Kieran Broadbelt, Kevin Pimbblet, Daniel Farrow et al. (+1 more)

Small-scale interactions such as minor mergers, flybys and harassment are considered common driving mechanisms that can both initiate and quench star-forming processes within post-starburst (PSB) galaxies. PSBs have been linked to disturbed morphologies and faint tidal features in numerous works. We aim to independently study these features in E+A galaxies found in the Galaxy and Mass Assembly Fourth Data Release (GAMA DR4). Using image stacking techniques, we derive the averaged radial surface brightness profiles of E+A image stacks alongside the Sérsic parameters that best fit these profiles. These E+A stacks consist of 57 images extracted from the Sloan Digital Sky Survey (SDSS) in g, r & i bands. The E+A stacks are shown to have brighter extended regions than similar non-PSB galaxies, which is indicative of faint tidal features that could be caused by small-scale interactions. Additionally, we make use of Dark Energy Spectroscopic Instrument (DESI) Legacy Survey imaging, which is deeper than SDSS, to further support our conclusions and find that the Legacy Survey images independently strengthen the evidence for excess light at extended radii relative to the comparison samples. We discuss these findings in the context of future surveys such as the Vera C. Rubin Legacy Survey of Space and Time (LSST) survey.
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All authors Kieran Broadbelt, Kevin Pimbblet, Daniel Farrow, Sugata Kaviraj