Peer Revenue An exchange of ideas

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 24 June

High Energy Astrophysical Phenomena

Study for curvature radiation and magnetic pair creation process on polar-cap region of magnetic white dwarf

Bingyan Wang and Jumpei Takata

Rapidly rotating, strongly magnetized white dwarfs (WDs) have been proposed as potential sites of rotation-powered activity analogous to that of a neutron star pulsar. In this study, we investigate particle acceleration, radiation processes, pair creation and resulting synchrotron radiation in the polar cap acceleration region. Within the framework of the space-charge-limited flow model, we examine how these processes depend on the spin period and surface magnetic field using both one-dimensional numerical calculations and analytical estimates. To explore the impact of the magnetic field geometry on the accelerating process, we consider both a pure dipole field and a combination of dipole and quadrupole fields. The inclusion of a quadrupole component reduces the curvature radius of the magnetic field lines, and significantly enhances the accelerating field, leading to more efficient radiation and pair creation processes. Using this framework, we evaluate the WD death line with a more consistent treatment of the relevant physical processes than the previous studies. We find that the pair creation process can occur for spin periods $P\lesssim100$~s, when the dipole field strength $B_{*,d}\lesssim10^{10}$~G, indicating that pair creation is difficult to sustain in currently known magnetic WDs. We discuss the implications of our model for rotation-powered activity in rapidly spinning isolated magnetic WDs and for the possible WD interpretation of long-period radio transients.
Read the full abstract

Astrophysics of Galaxies

AGN Jets from Formation to Dissipation

Anne-Kathrin Baczko, Eleni Vardoulaki, Etienne Bonnassieux et al. (+26 more)

Active Galactic Nuclei (AGN) are among the most energetic phenomena in the Universe, capable of launching powerful relativistic jets that extend from sub-parsec to megaparsec scales. These jets play a crucial role in regulating star formation, redistributing energy and matter, and shaping the evolution of galaxies and their environments. Despite decades of study, a comprehensive understanding of how AGN jets form, propagate, and dissipate remains elusive. The aim of this chapter is to highlight how the future capabilities of the the Square Kilometre Array (SKA), as a standalone array as well as in combination with Very Long Baseline Interferometry (VLBI) arrays and multi-wavelength facilities, will transform our capabilities to study the co-evolution of AGN jets and their host galaxies from jet formation to dissipation scales.
Read the full abstract

All authors Anne-Kathrin Baczko, Eleni Vardoulaki, Etienne Bonnassieux, Manel Perucho, Marisa Brienza, Marcus Brüggen, Emmanuel K. Bempong-Manful, Robert Beswick, Florian Eppel, Damien Gratadour, Jonas Heßdörfer, Kiara Hervella-Seoane, Matthias Kadler, Jae-Young Kim, Aretaios Lalakos, Leah K. Morabito, Dhanya G. Nair, Felix Pötzl, Jack Radcliffe, Luca Ricci, Eduardo Ros, Jan Röder, Florian Rösch, Ainara Saiz-Pérez, Hrishikesh Shetgaonkar, Cyril Tasse, Francesco Ubertosi, Jun Yang, J. Anton Zensus

Earth and Planetary Astrophysics

Substructures in Planet-Forming Disks with the SKAO

Yinhao Wu, Jessica Speedie, Sebastián Pérez et al. (+33 more)

Disks of gas and dust orbiting young stars are the arenas and material reservoirs for planet formation. Over the past decade, multiwavelength observations, from infrared to radio, have resolved the spatial distribution of hundreds of protoplanetary disks in nearby star-forming regions, revealing a diverse zoo of substructures. These substructures are morphological features such as rings, gaps, spirals, vortices, asymmetries, warps, or clumps that trace variations in density, temperature, or composition relative to an otherwise smooth distribution of gas and dust. Many unknowns persist as to the origin of these substructures, their role in planet assembly, and their true properties. SKA-Mid Band 5b continuum observations, offering angular resolutions of $\sim 0.05''$ ($\sim 0.15''$) with AA4 (AA*) at $12.5$ GHz / $2.4$ cm, will enable new progress at this frontier. In this chapter, we outline the open questions in the field of disk substructure that SKA-Mid is uniquely poised to address, with a lens on dust thermal emission.
Read the full abstract

All authors Yinhao Wu, Jessica Speedie, Sebastián Pérez, John D. Ilee, Takahiro Ueda, Claudia Toci, Daniel J. Price, Asmita Bhandare, Eleonora Bianchi, Tilman Birnstiel, Richard A. Booth, Tyler L. Bourke, Gemma Busquet, Simon Casassus, Yi-Xian Chen, Claudio Codella, Nicolás Cuello, Ruobing Dong, Antonio Garufi, Greta Guidi, Cassandra Hall, Haochang Jiang, Izaskun Jiménez-Serra, Hauyu Baobab Liu, Mayank Narang, Elenia Pacetti, Jaime Pineda, Paola Pinilla, Linda Podio, Danai Polychroni, Giovanni Sabatini, Eugenio Schisano, Leonardo Testi, Diego Turrini, Marion Villenave, David Wilner

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

Dark Photons from Red Dwarfs

Stefan Vogl and Xun-Jie Xu

Light dark photons can be produced in stellar systems and thus contribute to the stellar cooling rate. The additional cooling changes the evolution of the star and has an impact on various observable properties such as radius, photon luminosity or the emitted neutrino fluxes. This has been exploited before to derive limits based on observations of the Sun, horizontal branch stars and red giants. Given the wealth of astrophysical data collected in the last decade and the improvements in modeling stellar evolution it is interesting to investigate whether other stellar systems offer a complementary avenue towards testing dark photons. In this work, we study the effect on an alternative class of stars. We focus on the impact of dark photon induced cooling on red dwarfs, i.e. the lowest mass stars on the Hydrogen main sequence. Running simulations of the evolution of red dwarfs with dark photon cooling we determine the impact on the mass-radius relation. Combining our simulations with precise determination of mass and radius derived from observations of eclipsing binaries that have recently become available, we derive competitive limits which outperform the solar ones in a significant part of the parameter space.
Read the full abstract

Earth and Planetary Astrophysics

Young asteroid pair candidates in the Jovian Trojan population

Jindřich Žižka

The number of asteroid pairs, unbound asteroids with a common origin and similar heliocentric orbits, has increased rapidly since their discovery. However, to date, only a small number of asteroid pairs have been identified in the outer main belt and especially within the Hilda and Jupiter Trojan populations. Except for a few binaries and collisional families, only one 360 Myr-old pair (258656) 2002 ES76 - (635224) 2013 CC41 is known among the Jupiter Trojans. During our survey, using GPU-accelerated integrations of the Jovian swarms, we identified two new promising pair candidates younger than 2.5 Myr. Pair (264119) Georgeorton - 2024 CN most likely formed either 427-500 kyr or 527-536 kyr ago, whereas pair (8060) Anius - (542262) 2013 BL has an estimated age of 2367-2421 kyr. Our results show that young asteroid pairs can arise even within the sparse population of Jupiter Trojans, opening new questions about their formation.
Read the full abstract

Astrophysics of Galaxies

Exploring the physics of ram pressure stripping with radio continuum observations in the SKA era

Alessandro Ignesti, Ian D. Roberts, Henrik W. Edler et al. (+4 more)

Satellite galaxies in clusters are significantly more likely to be red and passive than similar mass galaxies in the field. This fact is known as the environmental quenching of galaxy star formation, which is believed to be driven by ram pressure stripping (RPS). The large velocity differences between the infalling galaxies and the intracluster medium (ICM) result in a strong ram pressure on their interstellar medium (ISM), which can strip it from the stellar disk. The stripped ISM can be studied at various wavelengths, including the radio band, thanks to the synchrotron emission produced by the magnetic fields and relativistic electrons embedded in them. This emission is typically steep-spectrum and thus best observed at low frequencies. Thus, continuum studies of the RPS effect are currently mostly carried out with LOFAR, limiting them to the northern hemisphere. SKA-Low will permit us to extend them to the southern sky, where they will synergize with the southern observatories and the upcoming ELT. Lastly, the sub-arcsecond resolution provided by SKA-Mid will facilitate the exploration of the polarization and filamentary structure of RPS radio tails and allow us to detect them up to $z\simeq0.5$, advancing our understanding of the impact of RPS on satellite galaxies in clusters and groups.
Read the full abstract

All authors Alessandro Ignesti, Ian D. Roberts, Henrik W. Edler, Myriam Gitti, Reinout J. van Weeren, Paolo Serra, Pavel Jachym

High Energy Astrophysical Phenomena

Multi-Band Optical Variability of Blazar 1ES 2344+514 on Diverse Time-Scales

Aykut Özdönmez

This study presents the results of multi-band observations from 2022 to 2024 and Zwicky Transient Facility (ZTF) observations from 2018 to 2023, examining the flux variability of the blazar 1ES 2344+514 on diverse time-scales in the optical bands. The blazar has mild short-term variability (STV) and long-term variability (LTV), with small amplitudes of $\sim0.7$ mag and 0.4 mag for the host subtracted- and included-light curves, respectively. The power-enhanced F-test and the nested Analysis of Variance (ANOVA) statistical tests of the six intra-day light curves show that the blazar has no minute-scale variability. The multiband color behavior analysis revealed a moderate redder-when-brighter (RWB) trend on intra-day time scales, while the LTV shows no detectable color behavior. We found a strong correlation between the ZTF optical light curves without any time lag, but no detectable correlations for the optical band emissions. From our periodicity searches using WWZ and LS methods, three significant quasi-periodic oscillation (QPO) signals in the ZTF light curves are found at about 1.02, 1.3, and 2.85 years. The observational results indicate that the blazar 1ES 2344+514 has a complex variability while emphasizing the need for future observations to unravel its underlying mechanisms.
Read the full abstract

Cosmology and Nongalactic Astrophysics

The SKA View of Cool-core Clusters: Evolution of Radio Mini-halos and AGN Feedback

Myriam Gitti, Paolo Tozzi, Francesco Ubertosi et al. (+12 more)

In about 70 per cent of relaxed, cool-core galaxy clusters, the brightest cluster galaxy (BCG) is radio loud, showing non-thermal radio jets and lobes ejected by the central active galactic nucleus (AGN). In recent years such relativistic plasma has been shown to interact with the surrounding thermal intra-cluster medium (ICM) as revealed by striking images where radio lobe fill the cavities in the X-ray-emitting gas. This "radio-mode feedback" phenomenon is widespread and crucial for understanding the physics of cluster cores and the properties of the central BCG. Mechanically-powerful AGN are expected to drive turbulence in the central ICM which may also contribute to the origin of non-thermal emission on cluster-scales. Diffuse non-thermal emission has been observed in many cool-core clusters in the form of a radio mini-halo surrounding the radio-loud BCG on scales comparable to the cooling radius. Large samples of mini-halos are essential to clarify their origin and their link with the thermal and dynamical properties of clusters, especially in view of future high-resolution X-ray studies with NewAthena X-IFU. All-sky surveys with the SKA-Mid telescope at arcsecond resolution would have the potential to detect up to about 3500 mini-halos at redshift z<1 (compared to the few tens currently known). Deep Tier surveys with the SKA-Mid at sub-arcsecond resolution would further enable a complete census of radio-loud BCGs down to 1.4 GHz powers of 10^23 W/Hz up to z~2. This will provide a comprehensive view of AGN feedback and its role in shaping large scale structures.
Read the full abstract

All authors Myriam Gitti, Paolo Tozzi, Francesco Ubertosi, Annalisa Bonafede, Gianfranco Brunetti, Rossella Cassano, Stefano Ettori, Luigina Feretti, Marie-Lou Gendron-Marsolais, Simona Giacintucci, Julie Hlavacek-Larrondo, Alessandro Ignesti, Giulia Macario, Mamta Pandey-Pommier, Tiziana Venturi

Cosmology and Nongalactic Astrophysics

Probing High-redshift Intracluster Medium Using SKA

Ramananda Santra and Ruta Kale

Galaxy clusters host vast reservoirs of magnetised plasma in their intracluster medium (ICM), where turbulence and shocks generated during structure formation sometimes give rise to diffuse synchrotron emission in the form of radio halos and relics. However, the origin and amplification of the magnetic field in the ICM remains among the least understood problems, particularly at high redshift, where direct detections are scarce. Recent observations of clusters at z $\gtrsim 0.6$ have revealed radio powers of the diffuse sources comparable to those of nearby systems, implying that efficient magnetic amplification suppressed inverse Compton losses. Such rapid growth of the magnetic fields after a few Gyrs of the Big Bang challenges standard dynamo timescales, and it raises fundamental questions about the mechanisms that strengthened cluster magnetic fields. In this chapter, we highlight the massive merging system El Gordo (ACT-CL J0102$-$4915, z$\sim$0.87) as a unique testbed for investigating theoretical models under extreme conditions. Proposing as a SKA science verification target, El Gordo will allow detailed studies of the ICM magnetic field structure, strength through broadband continuum and polarisation measurements with SKA-Low and SKA-Mid, across staged deployments starting from AA0.5 to AA4, reaching a physical resolution of $\sim$ 20-30 kpc at our redshift of interest. We further outline how upcoming SKA surveys will build statistical samples of high-redshift clusters, enabling tests of different models of magnetic fields and cosmic rays in the formation of large-scale structure.
Read the full abstract

Astrophysics of Galaxies

Ly$\rm \alpha$ halos and UV continuum morphologies of Tadpole Galaxies at $z> 3$

Manish Kataria and Kanak Saha

Tadpole and clump-chain galaxies are a morphologically distinct population among high-redshift star-forming galaxies whose disturbed structures may influence the escape and propagation of Ly$\alpha$ photons. We investigate the Ly$\alpha$ and UV continuum properties of 12 tadpole galaxies in the redshift range of z $\sim$ 3 – 5.5 identified in the Hubble Ultra Deep Field (HUDF) using deep MUSE observations. Accounting for their elongated morphologies, we construct surface brightness profiles and characterize the spatial extent of their Ly$\alpha$ emission. Extended Ly$\alpha$ halos are detected in 10 of the 12 galaxies, demonstrating that diffuse Ly$\alpha$ emission is common among tadpole systems. Approximately 40% of the sample exhibits double-peaked Ly$\alpha$ profiles. While the effective radii ($\rm R_{e}$) of the Ly$\rm \alpha$ emission generally follow the spatial extent of the UV continuum, the Ly$ \rm \alpha$ halos are typically more symmetric and often exhibit spatial offsets from the stellar component. Some galaxies also display asymmetric and outflow-like Ly$\rm \alpha$ structures suggestive of anisotropic escape and complex radiative transfer effects. Together, these results suggest that the disturbed morphologies of tadpole galaxies may influence the transport of Ly$\rm \alpha$ photons and contribute to the formation of extended Ly$\rm \alpha$ halos in the circumgalactic medium.
Read the full abstract

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

$K^-$-Driven Direct Urca Cooling in Rotating Neutron Stars: A Bayesian Study

Aprajita Shrivastava, Debanjan Guha Roy and Sarmistha Banik

We investigate the onset of antikaon ($K^-$) condensation and its implications for the equation of state (EoS) and cooling of neutron stars (NSs) within density-dependent relativistic mean-field parametrisations DD2 and MPE. Treating the antikaon - nucleon optical potential ($U_K$) as a free parameter in the range $[-180,-60]$ MeV, we constrain it using Bayesian inference with NICER mass-radius observations of PSR J0030+0451 and PSR J0740+6620. The inferred posterior distributions favour strongly attractive in-medium $K^-$ interactions, while their broad widths indicate only weak constraints on $U_K$ by astrophysical observations. More attractive values of $U_K$ lead to an earlier onset of $K^-$ condensation, enhanced softening of the EoS, and lower Direct Urca (DU) threshold densities. The condensation threshold is systematically lower in DD2 than in MPE, while finite entropy further promotes the onset of rapid cooling. The $K^-$-induced enhancement of the proton fraction ($y_p$) substantially affects a larger volume of the stellar core, i.e. capable of sustaining rapid DU cooling. We further show that rapid rotation suppresses DU cooling by reducing the central density and $y_p$, thereby shrinking the DU-active core. This suppression is more pronounced for MPE than for DD2. Our results demonstrate that $K^-$ condensation, finite entropy, and rotation jointly exert a strong influence on the conditions for rapid neutrino cooling in NSs.
Read the full abstract

Instrumentation and Methods for Astrophysics

DANTE: A Reference-Guided Unsupervised Pipeline for Extended-Transient Anomaly Characterization in LIGO O4a

Luca Cirfeta

The analysis of gravitational-wave detector data during the fourth observing run (O4) requires robust methods to distinguish stationary instrumental noise from non-stationary transients (glitches). In this work, we present DANTE (Domain-Adaptive Network for Transient Evaluation), a pipeline designed to discover and triage novel non-stationary artifacts entirely without labels. We demonstrate that adapting a pre-trained Vision Transformer (DINOv2) to extract local patch embeddings from time-frequency spectrograms allows for high-resolution mapping of transient anomalies. We formalize the Signal Dilution Barrier via controlled injection tests, showing that while Multiple Instance Learning (MIL) Top-k pooling recovers extended topologies, it is blind to sub-second morphologies. To address small-sample taxonomy instability, we introduce an adaptive Dirichlet Process Mixture Model (DPMM) that dynamically selects covariance structures. Finally, by implementing a native O4a background recalibration, we resolve the domain-shift problem, demonstrating consistency with the hypothesis that pervasive O4a morphologies (initially flagged as novel by historical references) are stationary artifacts. We conclude that unsupervised anomaly detection strictly requires native recalibration to filter domain-shift artifacts, while definitive classification of remaining unmodeled singletons requires multi-channel validation.
Read the full abstract

Astrophysics of Galaxies

Tracing the Star Formation History of the Universe through Thermal Free-Free Emission with the SKA

Hiddo S. B. Algera, Mark Sargent, Eric J. Murphy et al. (+1 more)

One of the major scientific aims of the SKA is to trace the history of star formation across cosmic time. High-frequency radio surveys are indispensable in this regard, as these are capable of probing thermal free-free emission (FFE) – the dominant component of the radio continuum of star-forming galaxies above rest-frame frequencies of $\gtrsim25\,$GHz. FFE is a powerful, direct star-formation rate (SFR) indicator, which robustly traces the number of ionizing photons produced by recently formed massive stars in a nearly dust-unbiased manner. In this chapter, we forecast the ability of the SKA to detect FFE in typical star-forming galaxies in the early Universe. Our starting point is the state-of-the-art T-RECS simulation suite of the faint radio sky, to which we apply an ambitious, matched-depth, multi-band AA4 SKA-Mid survey in Bands 1 through 5b, covering an area of $0.25\,\mathrm{deg}^2$ across $0.35 - 15.4\,\mathrm{GHz}$. We predict that such a survey will detect $\sim1.5\times10^4$ star-forming galaxies in all bands out to $z\approx7$, and perform simulations using established fitting techniques to investigate the accuracy with which their thermal FFE can be recovered. We find that thermal fractions ($f_\mathrm{th}$) and synchrotron spectral indices can be constrained in an unbiased manner, and predict uncertainties on the thermal SFRs of $\lesssim 0.1\,\mathrm{dex}$ for galaxies at the knee of the radio luminosity function across redshift. Convolving the distribution of $f_\mathrm{th}$ inferred from the multi-band SKA-Mid survey with wider luminosity function determinations at low radio frequencies will yield robust constraints on the total cosmic star formation rate density out to $z\sim7$.
Read the full abstract

All authors Hiddo S. B. Algera, Mark Sargent, Eric J. Murphy, Fangxia An

Earth and Planetary Astrophysics

Unveiling the Trans-Neptunian Region with the SKA

Pablo Santos-Sanz, Yücel Kilic, Thomas G. Müller et al. (+3 more)

We explore the potential of the SKA staged delivery AA4 (SKA-AA4) to detect and characterise the thermal emission of trans-Neptunian objects (TNOs) and Centaurs at centimetre wavelengths. These distant icy bodies preserve important information on the formation and evolution of the outer Solar System and provide a valuable link to planetary systems observed around other stars. The unprecedented sensitivity of SKA-AA4 will enable thermal detections of several of the brightest TNOs and Centaurs, extending radiometric studies beyond the capabilities of current radio facilities. Combined with shorter-wavelength observations and occultation measurements, these data will provide new constraints on spectral emissivity behaviour, thermophysical properties, and subsurface structure. At its highest angular resolutions, SKA-AA4 may partially resolve the largest systems, enabling investigations of surface heterogeneity, extended structures such as rings, and the partial resolution of some wide binary systems. We also assess the feasibility of radio occultation observations, which can provide independent constraints on object sizes, shapes, atmospheres, rings, or satellites. Together with observations from ALMA, JWST, and occultation campaigns, SKA-AA4 will establish centimetre-wavelength studies as a powerful new tool for investigating the thermal and structural properties of outer Solar System bodies.
Read the full abstract

All authors Pablo Santos-Sanz, Yücel Kilic, Thomas G. Müller, Emmanuel Lellouch, Javier Moldón, Jorma Harju

Earth and Planetary Astrophysics

Changes in Pluto's Atmosphere Based on Stellar Occultation Data from 2017 to 2023

Amanda A. Sickafoose, Michael J. Person, Carlos A. Zuluaga et al. (+14 more)

Pluto's tenuous atmosphere has $\mu$bar-level pressure and is composed primarily of ${\text{N}}_2$, with a variable haze. Its eccentric orbit combined with high obliquity leads to significant changes in solar insolation throughout the Plutonian year. The atmosphere is supported by vapor-pressure equilibrium with the surface ices, thus surface changes are coupled with the atmospheric properties. Volatile-transport models have anticipated Pluto's atmospheric evolution: predictions range from collapse over the coming decades to an atmosphere that remains. Previous work claims that Pluto's atmospheric pressure monotonically increased from 1988 through 2016, that the atmosphere began freezing out in 2018-2019, and that there was a plateau as of 2020. Here, we report results from ten stellar occultations by Pluto between 2017 August and 2023 July. Four events were multi-chord, while six were from single sites. Our results indicate a pressure plateau between the New Horizons flyby in 2015 through roughly 2021 and suggest that the atmospheric pressure has started to drop. Between 2015-2021 and 2022, the clear-atmosphere pressure at 1275 km decreased $7\pm6\%$, and it dropped $16\pm2\%$ for pressure at 1215 km when including haze. From 2017-2023, the upper atmospheric structure is consistent, while there is a change in light-curve slope in the lower atmosphere. This change-of-slope is consistent with haze particles settling over yearly or shorter timescales. Spikes in one light curve are indicative of intermittent buoyancy waves. More data are needed to confirm a recent pressure change.
Read the full abstract

All authors Amanda A. Sickafoose, Michael J. Person, Carlos A. Zuluaga, Amanda S. Bosh, Stephen E. Levine, Tim Brothers, Bastian Knieling, Timothy A. Lister, David J. Osip, Karsten Schindler, Joe Brimacombe, Tim Carruthers, Abigail Colclasure, Anja Genade, Petro Janse van Rensburg, Stephen B. Potter, Patricio Rojo

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

Exploring Gravitational Wave Science Frontiers with the SKAO

Nicola Bellomo and Philippa Cole

The Square Kilometre Array Observatory (SKAO) will be an important component of the global gravitational wave network. This article provides an overview of chapter eight of the Advancing Astrophysics with the SKA II (AASKAII) book, in which gravitational waves are a new addition, since the previous edition preceded the announcement of the first detection of gravitational waves in 2016. The chapter investigates the impact that this new observatory will have on numerous gravitational wave science cases. From testing General Relativity, to measuring the properties of the nanohertz gravitational wave background and exploiting new synergies with other upcoming experiments, the SKAO will play a key role in the next decades of gravitational wave science.
Read the full abstract

2606.25671 · 24 Jun · Published in Advancing Astrophysics with the SKA II (AASKAII), 2026 (arXiv:2606.20366). Report-no:AASKAII/Bellomo01. Advancing Astrophysics with the SKA II (AASKAII) outlines the transformative scientific advances that will be enabled by the SKA telescopes

Abstract PDF

Solar and Stellar Astrophysics

Multi-thermal dynamics and transverse oscillations of solar spicules revealed by coordinated SST, IRIS, and SDO observations

Ravi Chaurasiya, Tiago M. D. Pereira and A. Raja Bayanna

% context heading (optional) {Solar spicules are highly dynamic chromospheric jets that play an important role in the mass and energy balance of the solar atmosphere, though their connection to the transition region and corona remains unclear.} % aims heading (mandatory) {We investigate the dynamical and multi-thermal properties of spicules, their connection to higher atmospheric layers, and their transverse oscillations and associated energy flux.} % methods heading (mandatory) {We analyse coordinated high-resolution observations from the Swedish 1-m Solar Telescope (SST) in H$\alpha$, the Interface Region Imaging Spectrograph (IRIS) in \ion{Si}{iv} 1400~Å, and the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) coronal channels. Space-time diagrams, spectral analysis, and wavelet techniques are used to study temporal evolution, Doppler velocities, and oscillatory properties. Transverse displacements of spicules are tracked to estimate wave properties and energy flux.} % results heading {Space-time analysis reveals a clear correspondence between chromospheric spicules and coronal emission in AIA 171~Å, evolving coherently with spicule extension. Doppler velocities from H$\alpha$ and \ion{Si}{iv} show opposite signs, indicating multi-thermal plasma flows. Wavelet analysis reveals frequently dominant $\sim$3-minute oscillations, along with high-frequency transverse oscillations (65–270~s) with velocity amplitudes of 3.3–9.9~km~s$^{-1}$ and a mean energy flux of $(2.14 \pm 0.78)\times10^{3}$~W~m$^{-2}$.} % conclusions heading (optional) {These results demonstrate that spicules are multithermal, dynamic structures connected to the transition region and corona, and that transverse waves carry substantial energy, highlighting their role in coronal heating.}
Read the full abstract

Instrumentation and Methods for Astrophysics

VLT Beyond 2030 and Call for White Papers

Céline Péroux, Antoine Mérand and Martyna Chruślińska

The VLT Beyond 2030 conference gathered participants from the community and ESO experts to present and discuss science and technological ideas for the future of both the Very Large Telescope (VLT) and its interferometer (VLTI). An effort was made to pair participants with science and engineering backgrounds so as to optimise cross-field fertilisation and initiate 'out-of-the-main-room' discussions. The well-attended conference reflected the continued interest within our community in developing new projects for the VLT/I and the will to use this facility to answer key science questions that are likely to be crucial in the decades to come. This article presents a summary of the overall points of focus during the conference and also serves as the opening of the call for White Papers with a deadline of 15 January 2027. Proposers are encouraged to fast-forward to the years beyond 2030 to identify essential areas of research so that together we can shape a long-term roadmap for the VLT/I.
Read the full abstract

Astrophysics of Galaxies

Optical constants of Ih, Ic, and amorphous H$_2$O ices in the THz and IR ranges

A.A. Gavdush, F. Ribeiro, M.K. Matveishina et al. (+9 more)

Direct measurements of optical constants in the THz spectral region for astrophysically relevant H$_2$O ice samples are scarce. Extrapolation of optical properties in the THz spectral region from IR data can introduce uncertainties into astrophysical models. We measured the optical properties of water ice samples in the Ih and Ic forms as well as amorphous solid water (ASW) in the THz region in order to derive broad optical constants using literature and experimental data in the THz-IR range. In our experiments, the Ih, Ic, and ASW ices were grown by vapour deposition onto a cold substrate and measured by THz pulsed spectroscopy. Their THz optical properties were retrieved, compared with the THz-IR literature data, and approximated using the multiple-Lorentz model. From the existing literature data on the Ih, Ic, and ASW ices, we selected samples with the highest optical constants and classified them as compact. Their optical properties were merged in the frequency range of $\nu = 0.3$-$120$~THz (the wavelength range of $\lambda = 1$~mm-2.5$~\mu$m). The underlying absorption bands were attributed to vibrational modes and approximated using the multiple-Lorentz model while accounting for anharmonicity. Discrepancies primarily arising in low-absorption regions between the experimental data and broadband models were attributed to factors such as the model's complexity and the baseline-subtraction procedure. The THz response of all ices is formed by the low-frequency wings of the IR bands and the single broad low-intense THz peak around $1.8$~THz, which is very similar for all phases. The opacity calculation for dust grains covered by H$_2$O ice mantles based on experimental data shows discrepancies with data derived by extrapolation. The inferred THz-IR optical constants of water ice are important for future observations and modelling of cold clouds and protoplanetary disks.
Read the full abstract

All authors A.A. Gavdush, F. Ribeiro, M.K. Matveishina, A.Vyjidak, F. Kruczkiewicz, G.A. Komandin, S.V. Garnov, K.I. Zaytsev, A.V. Ivlev, T. Grassi, B.M. Giuliano, P. Caselli

High Energy Astrophysical Phenomena

A magnetically-supported disk-corona model for Changing-Look AGN transitions

Marios Kouzis, Agata Różańska, Debora Lančová et al. (+2 more)

Changing-Look Active Galactic Nuclei (CLAGN) undergo dramatic spectral and luminosity transitions on timescales of months to a few years – orders of magnitude shorter than the viscous timescale of a standard $\alpha$-disk at the radii where the optical/UV continuum is generated, for typical supermassive black hole masses. We show that a magnetically supported disk-corona model reproduces both the observed Eddington ratio at which changing event occurs and the observed transition duration. Using the diskvert code, which solves the steady vertical structure under simultaneous gas, radiation and magnetic pressure support with a self-consistent warm corona, we (i) construct thermal-viscous S-curves, and (ii) calculate the integrated thermal timescale together with the front propagation timescale. We compute a large grid of models of different black hole masses, Eddington ratios, magnetic viscosities, and disk radii, showing that magnetized disks push the S-curve knee down to an Eddington ratio of $ \approx 0.01-0.03$, and introduce a new stable branch of high luminosity solutions, while the limit-cycle timescale enters the months-to-years range for $M_\mathrm{BH} = 10^{7}-10^{9}\,\mathrm{M_\odot}$. Confronted with a sample of five CLAGN (Mkn 590, NGC 1566, IRAS 23226$-$3843, Mkn 1018, NGC 2617), the model jointly reproduces the empirical Eddington rates and the observed event durations only when the inner disk is strongly magnetized. The case of Mkn 590 is especially constraining: the recent tightly-determined transition Eddington ratio is matched by a highly magnetized disk-corona flow at small radii.
Read the full abstract

All authors Marios Kouzis, Agata Różańska, Debora Lančová, Bożena Czerny, Dominik Gronkiewicz

Solar and Stellar Astrophysics

Long-term Orbital Period Variations of the Eclipsing Dwarf Nova HT Cas

Aykut Ozdonmez, Huseyin Er, Ilham Nasiroglu et al. (+7 more)

We present a comprehensive analysis of the long-term orbital period variations in the short-period eclipsing dwarf nova HT Cas. By combining our new high-precision mid-eclipse times obtained between 2015 and 2026 with archival data, we constructed an updated $O-C$ diagram spanning a $\sim$48-years. Statistical analysis confirms outbursts do not cause systematic phase shifts, validating the use of all activity states. Through MCMC modeling, we show that the $O-C$ variations require a two-companion configuration. A free-eccentricity LTT model captures the variations but yields unconstrained posteriors and a highly eccentric outer orbit ($e_3 \sim 0.94$) that instantly collapses in N-body dynamical simulations. Imposing a circular constraint ($e=0$) resolves these mathematical degeneracies, yielding well-constrained posterior distributions. This dynamically stable model identifies two hypothetical circumbinary companions with minimum masses of $\sim 9.8 M_{Jup}$ and $\sim 5.0 M_{Jup}$, and periods of $\sim 32.6$ and $\sim 15.1$ years. Besides, this configuration inherently produces a negative quadratic term ($Q = -1.23 \times 10^{-14}$ days), aligning with secular period decrease predicted by standard CV evolution theory below the period gap. Refined energy-budget tests reveal that classical Applegate mechanisms require significantly more energy than the secondary star provides, indicating they cannot independently drive the modulations. While advanced magnetic frameworks may offer theoretical alternatives, our findings demonstrate that a dynamically stable two-companion architecture provides a highly robust and physically viable explanation, consistent with second-generation planet formation within a post-common-envelope disk.
Read the full abstract

All authors Aykut Ozdonmez, Huseyin Er, Ilham Nasiroglu, M. Emir Kenger, Murat Tekkesinoglu, Ergun Ege, Burak Batuhan Gürbulak, Ali Takey, Nazl{\i} Karaman, M. Abdelkareem

Instrumentation and Methods for Astrophysics

A Wideband Millimeter-wave Receiver at 210-350 GHz for LMT-FINER

Haoran Kang, Takafumi Kojima, Takeshi Sakai et al. (+9 more)

The Far-Infrared Nebular Emission Receiver (FINER) project is developing two wideband dual-polarization sideband-separating receivers covering 120-210 GHz and 210-350 GHz to efficiently identify high-redshift galaxy candidates in the early universe. Based on high-critical-current-density superconductor-insulator-superconductor mixer technology originally developed for the ALMA wideband sensitivity upgrade, the FINER receivers are designed to provide an intermediate-frequency bandwidth of 3-21 GHz per sideband and per polarization, approximately five times wider than the current ALMA specifications. After installation on the Large Millimeter Telescope, these receivers are expected to offer highly efficient spectral-scanning capability among (sub)millimeterwave facilities in the northern-hemisphere. This paper reports the initial laboratory characterization of the 210-350 GHz receiver. The measured single sideband receiver noise temperature is approximately 100 K over most of the radio-frequency band. Digital sideband separation was also demonstrated using a wideband spectrometer array (DRS4), achieving an image rejection ratio of around 20 dB in the initial tests. These results represent an important step toward the realization of a wideband spectral-scanning receiver system for FINER.
Read the full abstract

All authors Haoran Kang, Takafumi Kojima, Takeshi Sakai, Yoichi Tamura, Shun Ishii, Akio Taniguchi, Masato Hagimoto, Masato Kato, Taku Nakajima, Tai Oshima, Sho Masui, Issei Watanabe

High Energy Astrophysical Phenomena

Observation of A Solar Like Magnetic Reconnection Event in an AGN Corona with XRISM

Gal Vardi, Ehud Behar, Liyi Gu et al. (+14 more)

The X-ray source in AGN is commonly referred to as the corona by analogy to stellar coronae. The similarities between the two suggest that the heating mechanism of AGN coronae is magnetic reconnection – as in cool stars – but this has not yet been directly observed. This work presents the first observational evidence for a magnetic reconnection flare in an AGN corona. We report on a flare in NGC 3783, which was observed with XRISM/Xtend and XMM-Newton/EPIC-PN exhibiting distinct temporal evolution in soft ($<2.0\,$keV) and hard ($>2.0\,$keV) X-rays. An Ultra-Fast Outflow (UFO) was detected during the event. The flare features the Neupert effect – a temporal signature of the hard light curve correlating with the time derivative of the soft light curve, which shows that the flare is powered by magnetic reconnection, The Neupert effect is widely observed in the Sun, with Coronal Mass Ejections (CMEs) playing a role analogous to the UFO. We derive an upper limit of $30 \, R_g$ on the height of the magnetic loop from which the flare originates. Using the UFO's measured properties to characterize the magnetic field, we obtain $B > 1.3 \times 10^4\,$G for the field annihilated during the flare from total energy considerations, and $B \approx 500\,$G for the momentary magnetic field during reconnection from a dynamical consideration.
Read the full abstract

All authors Gal Vardi, Ehud Behar, Liyi Gu, Jelle Kaastra, Matteo Guainazzi, Missagh Mehdipour, Keigo Fukumura, Jon Miller, Ari Laor, Erin Kara, Megan E. Eckart, Misaki Mizumoto, Christos Panagiotou, Chen Li, Ogawa Shoji, Matilde Signorini, Keqin Zhao

Instrumentation and Methods for Astrophysics

A Non-Negativity Iterative Approach to Image Deconvolution for SKA

Le Zhang and Shiyu Li

We introduce a novel algorithm for image deconvolution applicable to interferometric radio observations, based on the assumption of non-negative source fluxes. The method enables rapid and efficient image reconstruction in an iterative manner, without requiring prior knowledge or training. Its computational cost scales linearly with the number of pixels: for example, a $512\times 512$ image can be processed in about 1-2 seconds on a standard laptop. We validate the algorithm using both point sources and an extended galaxy image, incorporating a realistic SKA-Low PSF with incomplete $uv$-coverage, though tests are conducted in noise-free simulations. Comparison with the CLEAN method demonstrates that our approach yields a good reconstruction, showing particular promise for the SKA and VLBI observations with sparse $uv$-coverage.
Read the full abstract

Instrumentation and Methods for Astrophysics

Application of Bayesian Statistical Tools to SKA Telescopes Polarization Surveys to Study Magnetization of the Large-scale Structure of the Universe

Valentina Vacca, Sebastian Hutschenreuter, Andrea Cabriolu et al. (+18 more)

Understanding cosmological magnetic fields requires a detailed knowledge of magnetism in the different environments of the large-scale structure of the Universe. Magnetic fields are well known to inhabit galaxy clusters, and recently their presence has been detected between galaxy clusters, along filaments extending up to 10-15 Mpc. Beyond that, there is limited information on the existence of magnetic fields in sheets and voids of the cosmic web. We propose a Bayesian statistical approach to study magnetic fields on large scales through observations of the Faraday rotation effect in large samples of polarized point-like background radio sources. We present the expectations to detect magnetization in environments of the large-scale structure with the SKA-Mid polarization survey planned by the SKAO Magnetism Science Working Group and with SKA-Low with AA4 telescopes, and discuss the required level of accuracy on the redshifts of the host galaxies for such a study. We find that about 50,000 mid-frequency Faraday rotation measurements complemented by high-precision redshifts are needed to constrain magnetization of dense environments as galaxy clusters. Investigation of magnetization in weakly-magnetized low-density enviroments, as filaments, will remain challenging, but low frequencies radio observations and spectroscopic redhifts for at least 17,000 will allow us to put first constraints.
Read the full abstract

All authors Valentina Vacca, Sebastian Hutschenreuter, Andrea Cabriolu, Torsten A. Ensslin, Philipp Frank, Jakob Roth, Martin Reinecke, Jens Jasche, Florent Leclercq, Ettore Carretti, Luigina Feretti, Chiara Ferrari, Federica Govoni, Cathy Horellou, Melanie Johnston-Hollitt, Francesca Loi, Matteo Murgia, Shane O'Sullivan, Rosita Paladino, Tessa Vernstrom, Gianni Fenu

Cosmology and Nongalactic Astrophysics

Euclid: Precise inference of defocus wavefront error from image diffraction spike measurements

D. Neumann, L. Miller, H. Hoekstra et al. (+146 more)

The success of the Euclid cosmological weak lensing measurements requires unprecedented knowledge of the point spread function (PSF) shape. Defocus wavefront errors induce variations in PSF size that directly bias inferred galaxy shapes. We present a rapid, model-independent estimator of the Euclid visible instrument defocus based on measuring subpixel shifts in diffraction spikes from bright stars, arising from the non-mirror-symmetric placement of the telescope spiders. This estimate requires no a-priori PSF model and can be directly inferred from individual survey exposures within seconds. We express defocus as the secondary mirror displacement along the optical axis, $\Delta z$, achieving a per-exposure precision of $\sigma(\Delta z) = 0.022\,\mu\text{m}$ in standard Euclid wide-survey images, corresponding to a peak-to-valley optical-path difference of $0.75\,\text{nm}$. This sensitivity resolves thermally induced shifts, typically 0.1-0.3$\,\mu\text{m}$, and enables tracking of temporal evolution and field-of-view variations when combining exposures within periods of stability. Since July 2024, the Euclid telescope has been exceptionally stable, while changes to defocus are effectively homogeneous across the field of view. By correlating defocus with PSF size, we find that the Euclid DR3 requirement of a fractional PSF size bias of $\left|\Delta R_\mathrm{PSF}^2/R_\mathrm{PSF}^2\right|<10^{-3}$ corresponds to field-averaged secondary mirror displacements exceeding $\langle \Delta z_\mathrm{thr}\rangle = (0.0683 \pm 0.0024)\,\mu\text{m}$. Our estimator provides a robust real-time monitoring tool, supplies a stringent prior for computationally intensive PSF model fitting, and is applicable not only to the Euclid telescope, but to other telescopes whose spider vanes are not mirror-symmetrically arranged.
Read the full abstract

All authors D. Neumann, L. Miller, H. Hoekstra, K. Kuijken, I. H. Whittam, N. E. Chisari, R. Nakajima, B. Altieri, A. Amara, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, S. Bardelli, A. Basset, P. Battaglia, A. Biviano, E. Branchini, M. Brescia, S. Camera, G. Cañas-Herrera, V. Capobianco, C. Carbone, J. Carretero, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, M. Cropper, H. Degaudenzi, G. De Lucia, H. Dole, F. Dubath, X. Dupac, M. Farina, R. Farinelli, S. Farrens, S. Ferriol, S. Fotopoulou, N. Fourmanoit, M. Frailis, E. Franceschi, M. Fumana, S. Galeotta, K. George, B. Gillis, C. Giocoli, P. Gómez-Alvarez, J. Gracia-Carpio, A. Grazian, F. Grupp, S. V. H. Haugan, W. Holmes, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, M. Kilbinger, R. Kohley, B. Kubik, M. Kunz, H. Kurki-Suonio, R. Laureijs, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, S. Mei, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, C. Moretti, L. Moscardini, C. Neissner, R. C. Nichol, S.-M. Niemi, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, A. Pezzotta, S. Pires, G. Polenta, M. Poncet, L. A. Popa, G. D. Racca, F. Raison, A. Renzi, J. Rhodes, G. Riccio, E. Romelli, M. Roncarelli, R. Saglia, Z. Sakr, D. Sapone, B. Sartoris, M. Schirmer, P. Schneider, T. Schrabback, A. Secroun, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, A. Spurio Mancini, L. Stanco, P. Tallada-Crespí, A. N. Taylor, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, L. Valenziano, J. Valiviita, T. Vassallo, A. Veropalumbo, Y. Wang, J. Weller, G. Zamorani, F. M. Zerbi, A. Gregorio, A. Loureiro, M. Sereno

Solar and Stellar Astrophysics

New Online Database of Symbiotic Variables: Catalog and Statistical Overview of Symbiotic Binaries

Jaroslav Merc, Rudolf Gális and Marek Wolf

We present the New Online Database of Symbiotic Variables (NODSV), a comprehensive and publicly accessible catalog of known and candidate symbiotic stars in the Milky Way and nearby galaxies. The database provides an up-to-date census of confirmed symbiotic binaries and systematically compiles information previously scattered across the literature, including photometric and spectroscopic properties, orbital parameters, and characteristics of both their cool and hot stellar components. It further records auxiliary diagnostics such as detected emission lines, flickering, X-ray emission, jets, or information about outburst activity. In its current release, NODSV contains nearly 1 400 objects, classified into confirmed symbiotic stars, three categories of candidates, and misidentified sources. Based on the collected data, though originating from heterogeneous studies, we present a statistical overview of the confirmed symbiotic population, highlighting the distributions of orbital parameters and the properties of the cool giants and their hot companions. Designed as a dynamic and evolving resource, NODSV provides a foundation for future observational campaigns and theoretical investigations of symbiotic binaries.
Read the full abstract

Cosmology and Nongalactic Astrophysics

Study of Polarized Emission in Radio Halos and Filaments in the SKA Telescopes Era

Valentina Vacca, Federica Govoni, Matteo Murgia et al. (+12 more)

Synchrotron diffuse emission in merging galaxy clusters and along filaments connecting them demonstrates the presence of relativistic particles and magnetic fields in these environments. The study of the polarized signal associated with this emission represents a powerful tool to constrain the properties of intracluster magnetic fields and the physics of acceleration and transport of relativistic particles. Despite technological progress, detecting this polarized signal is still very challenging. In order to shed light on the capabilities of the SKA telescopes to study this emission, we use the data of cosmological magneto-hydro-dynamic simulations to predict the expected polarized surface brightness of diffuse synchrotron sources from the center of galaxy clusters to filaments of the cosmic web at 1.4 GHz. We explore the possibility to detect these sources with a polarization survey with SKA-Mid with AA4 telescopes and compare the results with those from pointed observations corresponding to longer exposure times. These simulations provide precious information to understand the potential of the SKA telescopes for studying the origin and evolution of cosmological magnetic fields. We discuss how these observations can be used in order to characterize the magnetic field and the distribution and energy content of the radio emitting plasma and to shed light on the link between non-thermal and thermal properties and the dynamical state of the system.
Read the full abstract

All authors Valentina Vacca, Federica Govoni, Matteo Murgia, Paolo Marchegiani, Hui Li, Myriam Gitti, Francesca Loi, Luigina Feretti, Ettore Carretti, Elia Battistelli, Andrea Cabriolu, Torsten A. Ensslin, Chiara Ferrari, Gabriele Giovannini, Richard A. Perley

Instrumentation and Methods for Astrophysics

The Galaxy's Guide to the Tokenizer: A Benchmark for Scientific Foundation Models

Sogol Sanjaripour, Michael J. Smith, Manuel Pérez-Carrasco et al. (+3 more)

Tokenization is central to adapting scientific data for transformer-based foundation models, yet its impact on learned representations remains poorly understood. We compare four tokenization strategies, Affine, AIM, JetFormer, and VQ-VAE, within a unified transformer framework for astronomical imaging. Using 640,000 galaxy images from the DESI Legacy Survey and a shared AstroPT backbone, we evaluate each method on reconstruction fidelity and prediction of physical properties. Our results reveal trade-offs across approaches. The flow-based JetFormer achieves higher reconstruction quality, while VQ-VAE yields strong probe performance for galaxy physical properties. Affine and AIM better preserve localized morphological information. We find that reconstruction and representation quality are decoupled, and no single method consistently performs best across the tasks considered here. By grounding our evaluation in independently measured physical quantities, we hope this study serves to highlight the potential of scientific data as a basis for constructing interpretable benchmarks for foundation models.
Read the full abstract

All authors Sogol Sanjaripour, Michael J. Smith, Manuel Pérez-Carrasco, Juan Rafael Martínez-Galarza, Bahram Mobasher, Gabriela Canalizo

High Energy Astrophysical Phenomena

Probing Physical Conditions in Classical and Symbiotic Novae with the Square Kilometre Array Observatory

Rocco Lico, Marcello Giroletti, Arnau Aguasca-Cabot et al. (+9 more)

Cataclysmic variables and symbiotic stars are interacting binary systems in which a hot white dwarf (WD) orbits a companion main-sequence or red giant star, respectively. Accumulation of hydrogen-rich material on the WD surface may trigger re-ignition of thermonuclear reactions that, under degenerate conditions, lead to an explosive ejection of the accreted layer mixed with WD material. These explosions, known as classical novae, provide opportunities to study key astrophysical processes such as binary evolution, accretion, ionisation of circumstellar material, mass ejection, jet formation, and thermonuclear burning. Radio emission in these systems arises from both thermal and non-thermal processes, which manifest differently in classical and symbiotic novae. $\gamma$-ray emission has also been detected in several cases, and recent progress, driven by coordinated radio and multiwavelength observations, has greatly advanced our understanding of both types of novae. Multi-frequency, multi-epoch, and multi-scale interferometric observations are powerful probes of the evolving physical conditions following thermonuclear explosions, revealing information from both ionised and relativistic particle populations. The SKAO, particularly its SKA-Mid component, will enable regular monitoring of Galactic novae, multiple times per year for classical novae and every few years for symbiotic systems. It will explore a wide range of conditions, including companion types, WD masses, accretion regimes, and surrounding environments. The VLBI capabilities of the SKAO will target compact shocked regions, while its exceptional sensitivity will also allow characterisation of emission during quiescent phases of the binaries.
Read the full abstract

All authors Rocco Lico, Marcello Giroletti, Arnau Aguasca-Cabot, Joris Kersten, Benito Marcote, Ulisse Munari, Miriam M. Nyamai, Timothy J. O'Brien, Zsolt Paragi, Iris de Ruiter, Kirill Sokolovsky, David R. A. Williams