Solar and Stellar Astrophysics
Evolved massive stars and their impact on their environment
C.S. Buemi, G. Umana, C. Trigilio et al. (+15 more)
The comprehension of the final stages of massive
star evolution and their path toward the eventual
supernova explosion necessarily involves the study of
stellar winds and the circumstellar environment (CSE) surrounding them in the transitional phases, during which
stellar winds and eruptive mass loss profoundly shape the surrounding environment. The study of the pre-
supernova progenitors, from Red Supergiants, passing through the Luminous Blue Variable stage to Wolf-Rayet
stars, is of key importance because, focusing on their nebulae, they directly prove the mass-loss activity of the
star that, through wind and eruptive events, shapes the environment in which the
supernova will explode. Such environment, interacting with the ejecta, will heavily affect
supernovae spectrophotometric signatures. The Square Kilometre Array, with its extraordinary capabilities to combine high spatial resolution, sensitivity and wide frequency coverage will adress the most critical observational issues that currently prevent detailed characterization of CSE and, thus limit our ability to constrain its connections to
supernova and remnants proprierties.
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All authors C.S. Buemi, G. Umana, C. Trigilio, C. Bordiu, F. Bufano, J. van den Eijnden, S. Orlando, P. Leto, F. Bocchino, M. Miceli, M. Pérez-Torres, A. Alberdi, F. Cavallaro, L. Cerrigone, A. Ingallinera, S. Loru, S. Riggi, A.C. Ruggeri
Cosmology and Nongalactic Astrophysics
Constraining supermassive primordial black hole clustering with the angular auto-correlation of $z\simeq 6$ quasars
Zhan-He Wang, Hai-Long Huang and Yun-Song Piao
High-
redshift quasars provide a direct probe of the origin and environment of the earliest supermassive black holes. We use their angular auto-correlation function at $z\simeq 6$ to test scenarios in which supermassive
primordial black holes (SMPBHs) are associated with the observed
quasar population. The evolved PBH correlation functions, for both Poisson fluctuations and initial PBH clustering, are projected over the
quasar redshift window and compared with the measured angular correlation function using Markov chain Monte Carlo inference. It is observed that for the Poisson model, the posterior favors a small abundance, $f_{\rm PBH}\sim 10^{-3}$, and a supermassive effective mass scale, $m_{\rm PBH}\sim 10^{12}M_\odot$, interpreted here as a scale controlling
quasar host-
halo formation and clustering, and for the initially clustered model, the data prefer an effective clustering amplitude $\xi_{\rm eff}\simeq 2.1$ and a top-hat boundary scale $r_{\rm cl}\simeq 76\,{\rm Mpc}$, corresponding to weak relative contraction of PBH pairs in comoving coordinates.
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Cosmology and Nongalactic Astrophysics
The Impact of Dense RM Grids on the Study of Intra-cluster and Intra-group Magnetic Fields
Francesca Loi, Valentina Vacca, Shane P. O'Sullivan et al. (+8 more)
The presence of diffuse
radio sources in
galaxy clusters and the recent discovery of polarized signals associated with the tails of a jellyfish
galaxy indicates that intra-cluster/intra-group
magnetic fields can influence the physics of these environments and the
evolution of the embedded
galaxies. A better reconstruction of the properties of such fields is therefore fundamental to understand in detail the physical processes in
galaxy groups and clusters and the
evolution of the embedded sources. The SKAO represents a great opportunity to perform these studies through the analysis of the so-called rotation measure (RM) grid, since polarization properties of
radio sources are modified by the intervening
magnetic field. In this manuscript, we illustrate the prediction on the density of the RM grid considering the SKA-mid polarization survey planned by the SKA Magnetism Science Working Group. Moreover, we describe how it is possible to measure intra-cluster/intra-group
magnetic fields with the RM grid. Eventually, we quantify the improvement in the precision and accuracy of the
magnetic field measurements compared to what is achievable with current surveys such as the POSSUM survey.
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All authors Francesca Loi, Valentina Vacca, Shane P. O'Sullivan, Craig Anderson, Chiara Stuardi, Federica Govoni, Matteo Murgia, Annalisa Bonafede, Ettore Carretti, Filippo M. Maccagni, Tessa Versnstrom
Cosmology and Nongalactic Astrophysics
Slay the Shear: A Unified Statistical Framework for Weak Gravitational Lensing Shear Estimation
Shurui Lin, Xiangchong Li and Xin Liu
Weak gravitational
lensing shear measurements are fundamentally limited by shape noise arising from the intrinsic diversity of
galaxy morphologies. Upcoming surveys such as Rubin/LSST, Euclid, and Roman demand more flexible, statistically optimal approaches that can fully exploit high-dimensional image information. In this work, we develop a unified theoretical framework for shear estimation that connects classical response-based methods, shape noise, and modern machine-learning
estimators through the concept of the score function – the gradient of the image likelihood with respect to shear. We show that, for a general
spin-2 ellipticity definition, the ensemble shear response corresponds to an inner product between the
estimator and the score function, and that the score provides the minimum-variance unbiased shear
estimator. By incorporating response into the classical inverse-variance weight, we prove that the response-weighted inverse-variance weight is a general shape-noise-minimizing weight, independent of the intrinsic shape distribution. Furthermore, we propose Response-weighted Denoising Score Matching (RDSM) that exploits the remaining structure to reduce shape noise by ${\sim}17.5\%$ relative to moment-based methods at LSST 10-year depth while maintaining a multiplicative shear estimation bias below $2\times 10^{-3}$. Our result clarifies the optimality of existing calibration techniques while revealing a principled pathway for constructing improved
estimators via nonlinear shape transformations and learned representations.
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Astrophysics of Galaxies
A 3D tomography of the Local Bubble with SKA-Low
Xiaohui Sun, George Heald and Andrea Bracco
We know we reside in the Local Bubble (LB), but we know little about the magnetized gas inside the LB. The SKA-Low with more than half of the total number of stations distributed within 1 km distance provides enough short baselines and thus great surface brightness sensitivity. An SKA-Low polarization survey covering the frequency range of 50-350 MHz will deliver high-sensitivity and high-resolution images of diffuse polarized emission that originates from the local interstellar medium (ISM) and is probably related with the LB. Such a survey will also determine precisely the rotation measures (RMs) for the polarized structures using RM synthesis. These will allow us to reveal the 3D structure of the magnetized medium in the LB and to understand how the LB forms and evolves.
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Cosmology and Nongalactic Astrophysics
Weak Lensing with SKAO: Cosmic Shear Cosmology
Ian Harrison, Roberto Ingrao, Stefano Camera et al. (+4 more)
We discuss the power of weak gravitational
lensing surveys with the SKAO in constraining cosmological parameters and the properties of
radio star-forming
galaxy samples. As well as reviewing progress to date on
cosmic shear in
radio experiments, we show forecasts for parameter constraints using the Mid
telescope both alone and in cross-correlation with contemporaneous optical surveys. By selecting a sample of resolved, high-
redshift star-forming
galaxies in Band 2, surveys with the AA4 configuration will be capable of measuring the growth of structure on large scales in the Universe through the effect of weak gravitational
lensing on their shapes. Assuming the high fidelity reconstruction of such
galaxy shapes to be possible, we find that SKAO will measure the $S_8$ structure formation parameter to a level of $5\%$ alone and $3\%$ in full combination with either LSST or the Euclid satellite. These measurements will be highly important due to their radically different sensitivities to key weak
lensing systematics, both instrumental and astrophysical, and as such provide a vital robustness test to a pillar of modern cosmological measurements.
Radio surveys also provide unique and potentially game-changing information in the form of polarisation and
galaxy kinematics, which allow the cleaner separation of
lensing from intrinsic
galaxy shapes and can increase statistical power by factors $\sim5$-$10$.
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All authors Ian Harrison, Roberto Ingrao, Stefano Camera, Catherine Cress, Mamta Pandey-Pommier, Ziad Sakr, Cora Uhlemann
Astrophysics of Galaxies
The magnetic field in the Milky Way Galaxy: from large to small scales
Xiaohui Sun, Jennifer West, Marijke Haverkorn et al. (+6 more)
The Milky Way is the
galaxy in which we can study its
magnetic field to the finest details, providing an ideal laboratory to understand the fundamental questions: how
magnetic field is generated and evolves, and how it influences other components in the
Galaxy. An SKA-Mid polarization survey will produce an all-sky rotation measure (RM) grid with a density of about 100 per square degree, which is approximately two orders of magnitude larger than what is currently available, and produce total intensity, polarized intensity, and RM all-sky images of diffuse emission covering scales from about 10 arcseconds upward after combination with single-dish observations. The dense RM grid and images of diffuse emission will allow us to determine the most complete picture of the
magnetic field in the southern
Galactic hemisphere from large to small scales.
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All authors Xiaohui Sun, Jennifer West, Marijke Haverkorn, Andrea Bracco, Anna Ordog, Sui Ann Mao, Yik Ki Ma, Wenhui Jing, Thiem Hoang
Astrophysics of Galaxies
The OTELO Survey: The main sequence of low-mass galaxies
Bernabé Cedrés, Jordi Cepa, Carmen P. Padilla–Torres et al. (+15 more)
This paper describes the relationship between the
star formation rate and the
stellar mass, the so-called main sequence (MS), of low-mass
galaxies at three different
redshifts from the OTELO survey. In particular, we study Halpha at z=0.38, [OIII] at z=0.83, and [OII] at z=1.43 emission line
galaxies (ELGs). This is done to characterise the properties of low-mass ELGs. We fitted the spectral energy distribution (SED) of each emitter and obtained the
stellar masses, the total infrared luminosity, and the
star formation rate. We found that 100% of the Halpha emitters and about 90% of the [OIII] and [OII] emitters are low-mass
galaxies (< 1E10M_sun). We generated a MS for each
redshift regime, employing all
galaxies and binning them in
stellar mass. We obtained the parameters of the fit (turnover mass and slope of the low-mass regime) and compared them to results from the literature. We found that the colour-magnitude method employed to select ELGs leaves out a significant number of them. We also found that the whole sample contains few luminous infrared
galaxies and no ultra-luminous infrared
galaxies. We also found that the lack of infrared constraints in the input SEDs may generate problems when determining the total infrared luminosity. When comparing the MS obtained for our sample of low-mass ELGs with those from the bibliography, we found, in general, very good agreement. We can consider the MS to be almost the same for the relatively unexplored regime of low-mass
galaxies. However, the turnover mass obtained by this work is higher for all
redshifts compared with the ones from the literature. We suggest that this is an effect of the different methods and samples used in the generation of the MS compared to those of the bibliography.
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All authors Bernabé Cedrés, Jordi Cepa, Carmen P. Padilla–Torres, Ángel Bongiovanni, Miguel Cerviño, José A. de Diego, Jakub Nadolny, Simon B. De Daniloff, Mauro González–Otero, Monica I. Rodríguez, Jesús Gallego, Mirjana Pović, Maritza A. Lara–López, J. Ignacio González–Serrano, Miguel Sánchez–Portal, Ana María Pérez–García, Ricardo Pérez–Martínez, Emilio J. Alfaro
Instrumentation and Methods for Astrophysics
argosim: a Python package for radio interferometric simulations
Ezequiel Centofanti, Emma Ayçoberry, Samuel Farrens et al. (+4 more)
In this paper, we present argosim, a Python package for simulating
radio interferometric observations. The argosim package is modular, lightweight and compatible with all major operating systems. Its computational backend is written in JAX, which allows for greatly accelerated performance as well as the advantage of being fully differentiable. We detail the main argosim modules and describe how to use them to generate an observation, from the
antenna positions to the cleaned image. The package is a fully open-source project, and its code is publicly available on GitHub.
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All authors Ezequiel Centofanti, Emma Ayçoberry, Samuel Farrens, Samuel Gullin, Manal Bensahli, Jean-Luc Starck, John Antoniadis
Instrumentation and Methods for Astrophysics
Gravitational Light Deflection with SKA-VLBI and Its Application to Precision Tests of General Relativity
Y. J. Li, J. J. Li, Z. H. Lin et al. (+4 more)
Experimental test of general relativity remains an ongoing endeavour.
Radio astrometry provides a vital tool for precisely measuring the light deflection caused by the Sun, testing general relativity, and discriminating between gravitational theories. The best accuracy for the post-Newtonian relativistic parameter, $\gamma$, achieved with very long baseline interferometry is $9 \times 10^{-5}$. With 300-sec integration, SKA-VLBI can achieve a sensitivity of $\sim$15 $\mu$Jy at 15 GHz over a bandwidth of 0.256 GHz. This enables detection of $\sim$36 extragalactic
radio sources per square degree with flux densities of $\sim$1.5 mJy, and potentially detecting in-beam
radio sources. Single-epoch SKA-VLBI observations may achieve an astrometric precision of $\sim$2 $\mu$as. Utilising the Sun as a gravitational lens, 10-epoch positional tracking of extragalactic sources could improve $\gamma$ accuracy to $\sim$10$^{-7}$. Even with Jupiter as a lens, SKA-VLBI can measure $\gamma$ to $\sim$10$^{-4}$. Critically, it may conduct the first measurement of quadrupolar deflection of light caused by Jupiter, determining the physical oblateness of Jupiter, $J_{\mathrm{2, J}}$, to within $\sim${}$10^{-3}$. These advances are expected to rigorously test and improve gravitational theories or high-order parameterized post-Newtonian formalisms, while laying the foundations for (sub)$\mu$as astrometry.
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All authors Y. J. Li, J. J. Li, Z. H. Lin, D. J. Liu, Y. W. Dong, C. J. Hao, Y. Xu
High Energy Astrophysical Phenomena
Compact Objects Revealed by SKA and SKA-VLBI
Z. H. Lin, Y. J. Li, C. J. Hao et al. (+4 more)
Compact objects represent a crucial interdisciplinary frontier between astronomy and fundamental physics.The SKA/SKA-VLBI, with exceptional sensitivity (at $\mu$Jy levels) and ultrahigh positional precision (at $\mu$as levels), will enable direct, precise measurements of orbital dynamics in compact objects including black holes and
neutron stars. This facility is expected to achieve at least three breakthroughs: (1) Developing effective methodologies for detecting and identifying black hole-
neutron star binaries to construct observational catalogues, thus advancing investigations into the equation of state of ultra-dense
nuclear matter and strong-field relativistic effects; (2) Determining critical parameters such as orbital elements and component masses in compact binaries, yielding insights into
stellar structures and evolutionary mechanisms under extreme conditions; (3) Identifying intermediate-mass black holes and measuring their masses to deepen understanding of black hole formation and
evolution.
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All authors Z. H. Lin, Y. J. Li, C. J. Hao, J. J. Li, Y. W. Dong, D. J. Liu, Y. Xu
Cosmology and Nongalactic Astrophysics
Probing the Fundamental Nature of Particle Dark Matter
Marco Regis, Aritra Basu, Geoff Beck et al. (+7 more)
Understanding the fundamental nature of dark matter (DM) is one of the most significant scientific challenges of our time. A compelling hypothesis is that DM consists of a new, yet-to-be-discovered particle. Among the leading candidates are weakly interacting massive particles (WIMPs) and
axion-like particles (ALPs), both of which can be investigated using observations with the SKA
telescopes. In this chapter, we review the search for particle DM through
radio observations, summarizing the current state-of-the-art and presenting forecasts for the SKA-Low and SKA-Mid
telescopes in the AA4 baseline design.
Radio searches for WIMPs focus on detecting synchrotron radiation originating from the products of DM annihilation using continuum observations. Competitive constraints on sub-TeV WIMPs have already been derived using SKA precursors looking at
dwarf galaxies,
galaxy clusters, and the Large Magellanic Cloud. We discuss how the superior continuum sensitivity of the SKA
telescopes will allow us to progressively close in on the WIMP parameter space. The ALP signal arises from its decay or conversion into
photon(s), which typically consists of a nearly monochromatic signature, and from rotation of polarization angles of
photons interacting with ALPs. We demonstrate how the spectral resolution, line sensitivity, and polarimetry of the SKA AA4
telescopes can be leveraged to constrain the ALP-
photon coupling.
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All authors Marco Regis, Aritra Basu, Geoff Beck, Gianni Bernardi, Paolo Marchegiani, Dominik J. Schwarz, Marco Taoso, Elisa Todarello, Emma Tolley, Cora Uhlemann
Astrophysics of Galaxies
Studying HI and the Cosmic Web in the Era of SKA
Hengxing Pan, Martin Meyer, Madalina N. Tudorache et al. (+5 more)
Neutral atomic hydrogen plays a central role in the
evolution of
galaxies. Yet our understanding of how gas is accreted onto
galactic disks, and the way this is governed by the cascade of processes extending up to
cosmic web scales, remains poorly understood. The Square Kilometre Array has the potential to significantly advance our understanding in this field, being able to both resolve
galactic disks with high column density sensitivity, while also being able to survey the large volumes needed to understand the impact of processes at the level of the
cosmic web. In this chapter, we examine recent observational and theoretical progress made in this area, the potential contribution of the SKA, and needed
alignment with other
radio and multiwavelength facilities to advance the field.
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All authors Hengxing Pan, Martin Meyer, Madalina N. Tudorache, S. Lyla Jung, Maryam Arabsalmani, Gabriella De Lucia, Kristine Spekkens, Matt J. Jarvis
Solar and Stellar Astrophysics
Unveiling the nature of barium stars. I. Asteroseismic masses and the evolutionary link between Ba dwarfs and giants
Lupamudra Sarmah, Yerra Bharat Kumar, Simon W. Campbell et al. (+2 more)
Barium
star systems are excellent sites for studying AGB nucleosynthesis, binary
evolution, and mass transfer processes. However, an accurate estimation of their fundamental
stellar parameters is still lacking. Using TESS data, we made the first extensive asteroseismic mass measurements of 31 Ba
giants and 13 Ba
dwarfs. For some, we were able to measure $\Delta P$, ascertaining their evolutionary phase. We then constructed a grid of
stellar models across the relevant mass range, where we accreted AGB material using composition from existing yields. We found that the average masses of the Ba
dwarfs and Ba
giants are significantly different ($1.29\pm0.09~\rm{M}_\odot$ versus $1.96\pm0.16~\rm{M}_\odot$, respectively). However, their mass distributions peak around $1.3~\rm{M}_\odot$. While our sample of Ba
giants spans the low- and intermediate-mass regime, we found no intermediate-mass Ba
dwarfs. The abundance trends of $s$-process elements show an overall anti-correlation with
stellar mass, particularly in the low-mass regime. The
stellar models adopting Monash AGB yields can satisfactorily reproduce the observed light elements, $s$, and heavy-$s$ abundance trends, with an accreted mass of $0.1-0.5~\rm{M}_\odot$, but fail to explain the [hs/ls] ratio. Our results support an evolutionary scenario in which Ba
giants evolve from Ba
dwarfs, with mass
accretion occurring while the progenitor Ba
star is still on the main sequence. In this scenario, a substantial number of intermediate-mass Ba
dwarfs are expected. We found that post-
accretion additional mixing in our models is critical to explain the observed $s$-process abundances in Ba
dwarfs and the low C isotopic ratio ($<30$) in Ba
giants. The mismatch between the model and the observed [hs/ls] ratio suggests that the chemical enrichment of Ba
stars cannot be explained by standard single-
star AGB yields alone (abridged for arXiv).
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All authors Lupamudra Sarmah, Yerra Bharat Kumar, Simon W. Campbell, Sunayana Maben, Bacham E. Reddy
High Energy Astrophysical Phenomena
Accreting Compact Object Binaries with the SKA
Aru Beri, Francesco Carotenuto, Rob P. Fender et al. (+4 more)
Accreting binary systems provide a time-resolved view of the
accretion and ejection processes that are seen in all classes of compact objects, from
stellar-mass to supermassive. They allow us to study the launching of relativistic jets on human timescales, probing how the jets are coupled to the underlying
accretion flow, and providing unique insights that can be extended to supermassive black holes via the well-established mass scale invariance. Comparative studies of jets from different classes of compact objects allow us to determine the impact of mass,
spin,
magnetic fields, and
stellar surfaces on the launching of jets. The jets from black hole X-ray binaries provide probes of the
Galactic black hole population, and an important source of feedback to the surrounding interstellar medium. While existing
radio facilities (including the SKA precursors) have made great progress in this field in recent years, the SKA will enhance such studies via its high point source and surface brightness sensitivity, high angular resolution, and broad frequency coverage. This will enable the extension of our existing black hole studies to the fainter accreting
neutron star and white
dwarf population, the detection of previously-undiscovered systems in a low-luminosity quiescent state, and the extension of our studies to nearby
galaxies, revealing rare, high-
accretion rate systems that probe a key phase of black hole growth.
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All authors Aru Beri, Francesco Carotenuto, Rob P. Fender, James C.A. Miller-Jones, Sara Motta, Valeriu Tudose, Jakob van den Eijnden
Earth and Planetary Astrophysics
Physical Characteristics of the Asteroid (469219) Kamo'oalewa as a target of the Chinese Tianwen-2 mission
Xiaobin Wang, Karri Muinonen, Shenghong Gu et al. (+3 more)
The Near-earth asteroid (469219) Kamo'oalewa, a quasi-satellite of the Earth, is going to be observed in site and sampled by the Chinese space mission Tianwen-2 in near future. Here. we analyze its photometric and spectroscopic data to figure out its basic physical properties, which are very important for the sample return task of the Tianwen-2 mission. With photometry inversion methods, we derived a pole $(276^{o}.79, -21^{o}.43)$ with a
spin period of 28.4517 minutes and a slightly flat convex shape. The estimated photometry slope of $0.998 mag/rad$ implies a large albedo of the Kamo'oalewa, i.e. S-type. Using the estimated absolute magnitude of $24.98$ mag, its size could be 27.4m assuming a typical albedo of S-type asteroids. The taxonomy analysis with a constructed ANN tool also supports that the Kamo'oalewa should belong to S-type asreroids, it may be a strong weathering fragment of an A-type or Q-type asteroid. Using derived pole, size and shape information of the target, we estimated its thermal inertia as $163.0 Jm^{-2}K^{-1}s^{-1/2}$ based on the new derived Yarkovski draft $A_2=-13.29349563\times10^{-14}au/day^2$, which means the target has a surface of mixture of grains and small bounds, like the surface of asteroid Bennu.
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All authors Xiaobin Wang, Karri Muinonen, Shenghong Gu, Xin Liu, Xiyun Hou, Jing Huang
Astrophysics of Galaxies
Probing the ubiquity of complex ices in protostars with JWST: the first systematic quantification of weak ice bands between 6.8 and 7.9 micron
Yuan Chen, Ewine F. van Dishoeck, Katerina Slavicinska et al. (+18 more)
Complex organic molecules (COMs) are the key to understanding the chemical
evolution from simple interstellar molecules to potential prebiotic material. Although COMs have been extensively studied in the gas phase toward protostars, their counterparts in ices, where they are thought to form at earlier stages, remain far less constrained. A number of diagnostic features of complex ices lie between 6.8 and 8.8 um, a region known as the "COM ice fingerprint range," but previous infrared facilities lacked the sensitivity and spectral resolution required to quantify the weak bands therein. With the unprecedented sensitivity and resolving power of JWST, these limitations can now be overcome. Here, we present the first large-sample quantitative study of the absorption features at 7.02, 7.24, 7.40, and 7.67 um, using MIRI-MRS spectra of 21 protostars. The CH4 band at 7.67 um is the strongest band and shows remarkably uniform peak positions (7.67-7.68 um) and FWHMs (0.06-0.08 um), suggesting CH4 ice as its dominant carrier. The 7.24 and 7.40 um bands exhibit larger source-to-source variations in peak positions and FWHMs, but their occurrence and intensities are strongly correlated with each other. Comparisons with existing and new laboratory spectra suggest HCOO- as the most likely carrier of these two bands, yet HCOO- cannot fully reproduce their intensity ratios, implying additional contributions from other species such as C2H5OH, CH3CHO, and CH3COCH3. Our results reveal, for the first time, the potential ubiquity of weak features of complex ices in protostars, which have remained largely undetected due to observational limitations.
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All authors Yuan Chen, Ewine F. van Dishoeck, Katerina Slavicinska, Lukasz Tychoniec, Martijn L. van Gelder, Logan Francis, Adwin C. A. Boogert, Mayank Narang, Charlotte A. F. Schravendijk, Henrik Beuther, Alessio Caratti o Garatti, Eyze K. H. Eenhorst, Caroline Gieser, Thomas Henning, Manuel Gudel, Valentin J. M. Le Gouellec, Melissa K. McClure, Pooneh Nazari, Simon D. Reyes, Mees Tolman, Yao-Lun Yang
Solar and Stellar Astrophysics
Solar Radio Burst Fine Structures
Eduard Kontar, Daniel Clarkson, Hamish Reid et al. (+5 more)
Solar radio bursts exhibit intricate variability in time, space, and frequency, often displaying a rich variety of fine frequency-time structures such as spikes, drift pairs, striae in Type III bursts, and herringbone patterns in Type II bursts, etc. Historically, limited spatial, spectral, and temporal resolution has hindered detailed investigation of these narrow-band, rapidly evolving features, restricting progress in identifying their physical origins and underlying processes at these scales. Advances in high-time-frequency-resolution
solar imaging now offer transformative opportunities. Recent sub-second imaging spectroscopy has revealed that many fine structures challenge existing theoretical models, pointing to the need for new frameworks and a reassessment of current interpretations. The Square Kilometre Array (SKA), with its full-Stokes imaging spectroscopy at sub-second cadences, will provide unprecedented data essential for resolving these long-standing questions. These capabilities promise to significantly deepen our understanding of electron acceleration and transport,
magnetic reconnection, and coronal
plasma turbulence, thereby advancing our knowledge of
solar energetic processes and improving assessments of their space-weather impacts.
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All authors Eduard Kontar, Daniel Clarkson, Hamish Reid, Yingjie Luo, Nicolina Chrysaphi, Alexey Kuznetsov, Galina Motorina, Carine Briand
High Energy Astrophysical Phenomena
Amortized Simulation-Based Inference of Relativistic Mean-Field Couplings for Neutron-Star Equations of State
Prashant Thakur and Tuhin Malik
We present a simulation-based inference framework for constraining microscopic relativistic mean-field parameters of
neutron-
star equations of state. Neural posterior estimation is applied to two representative RMF families, a density-dependent DDB model and a nonlinear RMF-NL model, using
nuclear saturation properties,
chiral effective-field-theory pure-
neutron-matter pressures, and the maximum-mass constraint as conditioning observables. The inferred posteriors are validated against the conventional nested sampler (PyMultiNest) calculations and tested with the TARP coverage diagnostic. For both RMF parametrizations, the neural posterior reproduces the nested-sampling constraints on model couplings,
nuclear-matter properties, and
neutron-
star observables with no significant bias. The amortized
estimator generates $3\times 10^{4}$ posterior samples in about $2.5\,\mathrm{s}$ on a CPU, enabling a rapid inference workflow without the need for retraining for updated data. This constitutes a proof of concept that NPE-emulated RMF models, once validated, can be safely used for superfast exploratory inference. As an additional mock-observation test, imposing $R_{1.4}=12\,{\rm km}$ and $M_{\rm max}>1.97\,M_\odot$ leads to consistent predictions for the maximum-mass configuration, with DDB giving $M_{\rm max}=2.10^{+0.09}_{-0.07}\,M_\odot$, $R_{\rm max}=10.71^{+0.14}_{-0.21}\,{\rm km}$ and RMF-NL giving $M_{\rm max}=2.05^{+0.10}_{-0.06}\,M_\odot$, $R_{\rm max}=10.69^{+0.18}_{-0.19}\,{\rm km}$; although fixing $R_{1.4}$ confines both families to a narrow EOS region, RMF-NL remains marginally softer than DDB at high density, consistent with its slightly lower maximum mass.
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Solar and Stellar Astrophysics
Exploring Activity Across the Stellar Main Sequence with the Sun as a Benchmark
Atul Mohan, Stephen M. White, Sven Wedemeyer et al. (+1 more)
The active atmospheres of cool main-sequence
stars (F-M type) often release a fraction of their stored
magnetic energy, producing enhanced emissions (
flares) across
radio to X-ray wavelengths and associated space weather events like coronal mass ejections (CMEs) and energetic particle events (EPEs). Detailed imaging of active regions and CMEs, and in-situ EPE measurements are possible only in our Sun, making it a
benchmark for
stellar activity research. Multiwaveband
solar imaging
datasets let us define robust disk-integrated Sun-as-a-
star diagnostics of active region and space weather, extendable to
stellar datasets.
Radio waveband provide diagnostics of particle acceleration, CMEs and EPEs, essential to model
flare events and their space weather impacts. The Square Kilometre Array (SKA)
telescopes will facilitate sub-second scale spectropolarimetric imaging of the
solar corona across 0.05 - 15GHz, enabling detailed vertical tomographic studies of the active region across a range of coronal heights. Coupled with high energy instruments, the SKA
telescopes will allow well-constrained modeling of large samples of diverse active phenomena and the defintion of robust Sun-as-a-
star diagnostics of active region and space weather. Besides, the supreme sensitivity and angular resolution of the SKA
telescopes will help detect quiescent and active emissions from several nearby
stars. This chapter discusses the importance of comparative
solar-
stellar studies using Sun-as-a-
star diagnostics in understanding activity and associated space weather conditions in
stars across the cool main-sequence, and presents some research avenues that will benefit
solar and
stellar astrophysics.
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All authors Atul Mohan, Stephen M. White, Sven Wedemeyer, Vladimir Airapetian
Earth and Planetary Astrophysics
Resonant Super-Earths Dancing With EKL Oscillations: TTV Phase Excitation and Resonance Disruption by EKL Interactions between a Cold Jupiter and Stellar Companion
Pin-Gao Gu and Gongjie Li
Near-resonant Kepler
planets are dynamically hot, as evidenced by nonzero transit timing variation (TTV) phases, indicating that free eccentricities are not damped. Recent observations suggest that circulating near-resonant
planets tend to be dynamically unstable, and hence dynamically hot, likely representing an intermediate stage in the close-in super-Earth population at young ages. We investigate whether a cold Jupiter interacting with a
stellar companion through the eccentric Kozai-Lidov mechanism (EKL) can excite TTV phases and increase the libration amplitude of resonant angles in close-in resonant pairs. We find that the EKL model that drives the observed eccentricity of cold Jupiters can also excite TTV phases, increase the libration amplitude of resonant angles away from ideal
geometric alignment, and even disrupt them in a significant fraction of planetary systems in our simulated samples over 16 Myr. We also find that the TTV phases of the resonant pairs tend to be small (< 90 degrees), while the resonant angles are more easily elevated to become circulating during EKL excitation.
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Solar and Stellar Astrophysics
Ruijie Li, Chengyuan Wu, Zhibin Dai et al. (+1 more)
Accreting white
dwarfs (WDs) are considered one of the most promising progenitor candidates for Type Ia
supernovae (SNe Ia).
Dwarf novae (DNe), a subclass of cataclysmic variables (CVs), consist of a carbon–oxygen (CO) WD accretor and a low-mass donor
star, which may be either a main-sequence (MS)
star or a slightly evolved subgiant. Previous studies have suggested that, under the thermal–viscous disk instability mechanism, the time-averaged
accretion rate in long-period DNe may approach the regime of stable hydrogen burning, potentially allowing the WD to grow toward the Chandrasekhar mass, (M_Ch). However, whether such periodic
accretion can sustain stable hydrogen burning and lead to WD mass growth remains uncertain. In this work, we explore whether high
accretion rates on short periodic timescales can maintain stable hydrogen burning on the WD surface and drive the WD toward (M_Ch). Using Modules for Experiments in
Stellar Astrophysics (MESA), we investigate the mass-retention efficiency of WDs undergoing intermittent DN-like
accretion and examine its dependence on duty cycle,
accretion rate, and initial WD properties. We find that periodic
accretion fails to maintain stable hydrogen burning. During quiescent phases, the WD cools and becomes increasingly degenerate, leading to nova outbursts with progressively decreasing mass-retention efficiency and ultimately preventing further WD mass growth. We therefore suggest that DNe are unlikely to be progenitors of SNe Ia.
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All authors Ruijie Li, Chengyuan Wu, Zhibin Dai, Bo Wang
Solar and Stellar Astrophysics
Data-inspired simulation of AR 11158
Matthias Rempel and Georgios Chintzoglou
We present a data-inspired simulation of NOAA active region AR 11158. We simulate the formation of a collisional polarity inversion line (cPIL) by moving sunspots in a quadrupolar configuration along the centroid positions extracted from AR 11158. This process builds up free energy in the corona exceeding $4\cdot 10^{32}$ erg, out of which about $2\cdot 10^{32}$ erg are released in a X-
flare followed by a series of smaller
flares in the B to M range. The 4 strongest
flares are associated with coronal mass ejections. About 1-2 hours prior to the X-
flare a
magnetic flux rope (MFR) is forming above the cPIL. About 5 minutes before the
flare an upflow at chromospheric heights indicates a rise of the MFR. The eruption starts when parts of the MFR enter regions with a decay index larger than 1.5, indicating that the
flare initiation is consistent with the
torus instability. Comparing the series of
flares in this simulation to properties of observed
flares, we find a comparable trend between
flare energy and GOES X-ray flux, but
flare duration falls into the short end of the observed
solar distribution. As a consequence, energy fluxes into the
flare ribbons can be substantial, reaching $10^{13}$ erg cm$^{-2}$ s$^{-1}$ for the simulated X-
flare. The X-
flare causes step-function like changes of the horizontal
magnetic field in the photosphere, a propagation of a momentum pulse into the convection zone and quasi-periodic pulsations in the volume of the corona with periods from sub-seconds to multiple 10 seconds.
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Solar and Stellar Astrophysics
A Detailed Model Atmosphere Analysis of Cool White Dwarfs in DESI DR1
Mukremin Kilic, Pierre Bergeron, Simon Blouin et al. (+9 more)
We present a detailed model atmosphere analysis of cool white
dwarfs in the Dark Energy Spectroscopic Instrument Data Release 1 (DESI DR1). Our sample includes 25,642 unique targets with $G_{\rm BP}-G_{\rm RP}>0$. Unlike the hot DA white
dwarf sample in DESI DR1, we do not find a significant discrepancy between the photometric and spectroscopic masses for cool DAs. Hence, DESI's calibration problems for broad lines have a negligible effect for cooler DAs with narrower lines.
Magnetic DAs are found everywhere, and not just on the crystallization sequence, indicating that crystallization induced dynamos cannot solely explain the origin of magnetism in white
dwarfs. A detailed analysis of cool DC and DZ white
dwarfs indicates that the H/He abundance ratio in He-atmosphere white
dwarfs increases at lower temperatures. Based on the currently available models, this is the only way to keep the DC masses consistent with the average white
dwarf mass of $0.6~M_\odot$. Combined with the analysis of the hot white
dwarfs presented previously, this paper completes the analysis of 44,963 white
dwarf candidates with DESI DR1 spectra. We use this sample to constrain the fraction of He-atmosphere white
dwarfs as a function of temperature, and demonstrate that the He-fraction increases significantly below 10,000 K due to convective mixing. We also highlight rare systems, including new extremely low-mass, DA+DB, and DA+DQ binaries.
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All authors Mukremin Kilic, Pierre Bergeron, Simon Blouin, Adam Moss, Matthew J. Green, Gracyn Jewett, Manuel Barrientos, Alexander L. Albright, Alexander R. Gleason, Warren R. Brown, Nagaraj Vernekar, Michael R. Hayden
Astrophysics of Galaxies
A Statistical Study of HI Gas in AGN-Hosting and Satellite Galaxies from ALFALFA and FASHI
Shuanghao Shu, Wenkai Hu, Junqiang Ge et al. (+6 more)
We investigate the relative importance of Active
Galactic Nucleus (AGN) feedback and environmental processes using a large sample of HI
galaxies from the ALFALFA and FASHI surveys. By applying the optical spectroscopy from SDSS DR7/DR8 and the DESI survey, we analyse the gas content and physical properties of AGN-hosting
galaxies in group environments. Our results show that AGN-hosting
galaxies exhibit significantly suppressed
star formation rates and HI gas fraction, approximately one order of magnitude lower than
star-forming counterparts, regardless of their group-centric position. AGN-hosting satellites exhibit a significant and persistent deficit in both gas fraction and SFR relative to normal satellites without AGN, even at the
halo virial radius (R/R180 approx 1). This suggests that cold gas depletion is primarily driven by internal AGN feedback before these
galaxies experience intense environmental interactions. The relatively flat radial profiles of gas fraction and sSFR further indicate that the
evolution of AGN-hosting satellites is governed by internal physical processes rather than environmental interactions. Moreover, the apparent increase in HI gas at R/R180 < 0.3 is identified as an artifact of beam confusion. We conclude that for the AGN-hosting population, internal feedback is likely the prior quenching mechanism, while environmental effects act as a secondary, subsequent process.
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All authors Shuanghao Shu, Wenkai Hu, Junqiang Ge, Jinjiang Yu, Wenxiu Yang, Furen Deng, Yichao Li, Yougang Wang, Xuelei Chen
Astrophysics of Galaxies
Cosmological Galaxy Formation Modelling in the Era of the Square Kilometre Array
Claudia del P. Lagos, Carlton M. Baugh, Connor Bottrell et al. (+11 more)
Over the past decade,
galaxy formation simulations have advanced dramatically, transforming our ability to model the interstellar medium (ISM) and predict
galaxies'
radio emission. Yet the challenge of bridging physical scales–from sub-parsec
star formation to gigaparsec
cosmic structure–remains. The Square Kilometre Array (SKA) will map the cold gas and
radio continuum of
galaxies across
cosmic time, demanding models that couple physical realism with cosmological reach. This chapter reviews the state-of-the-art in cosmological
galaxy formation modelling in preparation for the SKA. We outline progress in simulating atomic hydrogen (HI), molecular gas, and
radio continuum emission from both
star formation and active
galactic nuclei, highlighting how cosmological hydrodynamical simulations and semi-analytic models now jointly reproduce many observed gas properties. We emphasise the need for a coordinated, “wedding-cake” strategy that unites simulations of different scales, for forward modelling of observables to ensure fair comparison with data, and for the integration of new technologies such as AI-driven emulators to accelerate progress. Together, these efforts will enable theoretical models to both interpret and guide SKA science, turning simulations from passive interpreters into active engines for discovery.
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All authors Claudia del P. Lagos, Carlton M. Baugh, Connor Bottrell, Romeel Dave, Gabriella De Lucia, Jindra Gensior, Filip Huško, Cedric G. Lacey, Danail Obreschkow, Kyle Oman, Chris Power, Nicole Thomas, Ruby J. Wright, Lizhi Xie
Instrumentation and Methods for Astrophysics
M-EPDet: Real-Time Real-Bogus Classification and Transient Candidate Judgement for the EP-WXT Pipeline via Multi-Modal Data
Lang Chen, Yunfei Xu, Zhen Zhang et al. (+8 more)
The Wide-field X-ray
Telescope (WXT) onboard the Einstein Probe (EP) produces a large post-detection candidate stream in which genuine astrophysical sources coexist with instrumental artifacts and
Cosmic Ray events. We present M-EPDet, a three-step post-detection framework for real-time candidate vetting in EP-WXT lobster-eye Micro-pore Optics (MPO) data. The framework combines a ResNet-based Arm filter, a dual-branch temporal-spectral
Cosmic Ray filter, and a background-aware
Bayesian Blocks module for single-exposure variability screening. Using on-orbit EP-WXT observations, we report decoupled metrics for the cascading system. M-EPDet achieves a Real-Bogus Recall of 98.31% ($98.53\% \times 99.78\%$) for genuine astrophysical sources, together with rejection rates of 92.99% for instrumental artifacts and 98.18% for
Cosmic Ray events. In the final step, the
Bayesian Blocks module flags 0.75% of the post-filtration observations, corresponding to a 99.25% reduction in candidate volume. The system is deployed in the EP-WXT pipeline as a lightweight real-time service, reducing the manual-inspection burden in candidate vetting.
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All authors Lang Chen, Yunfei Xu, Zhen Zhang, Dongyue Li, Hui Sun, Yuan Liu, Chenzhou Cui, Jinhui Xie, XiaoXiong Zuo, Shirui Wei, Wujun Shao
Cosmology and Nongalactic Astrophysics
A hybrid method for reconstruction of the equation of state of dark energy and its application to Pantheon+SH0ES data
Gawain Simpson, Krzysztof Bolejko and Stephen Walters
Cosmology aims to understand the physical properties of our Universe on its largest scales. One such feature is the expansion of the Universe, which currently seems to be dominated by a phenomenon referred to as dark energy. The physical nature and properties of dark energy are one of the main topics of investigation of modern cosmology. Observational cosmology aims to reconstruct the
evolution and the equation of state of dark energy, while theoretical cosmology aims to provide methods for such reconstructions and models explaining the nature of dark energy. If the equation of state, defined as the ratio of pressure to density $w = p/\rho$, deviates from $-1$, i.e. $w\ne-1$, then this would imply the existence of some sort of dynamical process behind dark energy. Most investigations assume a specific parametric form of $w$, eg. $w(z) = w_{0} + w_a z/(1+z)$, with $z$ being
redshift and $w_0$ and $w_a$ being constants. The analysis of the data is then reduced to fitting the model to the data. In this work, we take a different approach. Instead of imposing a predefined parametric form for $w(z)$, we reconstruct the equation of state indirectly from the dimensionless comoving distance $D(z)$ and its derivatives. This avoids assuming a specific physical parametrisation of dark energy, such as the CPL form, but still requires adopting functional representations for the distance–
redshift relation itself. The method should therefore be regarded as a hybrid or semi-parametric reconstruction approach: the parametrisation is shifted from the equation of state to the observable distance function. Finally we apply the method to the Pantheon+ SH0ES data. The results are consistent with dark energy being the cosmological constant, i.e. $w = -1$. Future surveys such as LSST will provide more data and narrow down the uncertainty. This in turn will yield tighter constraints on dark energy.
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High Energy Astrophysical Phenomena
Constraints on Line-of-Sight Acceleration from O1-O4
Labani Roy and Alexander H. Nitz
A compact binary will experience a center-of-mass (CoM) acceleration in the vicinity of a massive third object. The line-of-sight (LOS) component of this acceleration is imprinted on gravitational waves (GWs) produced by the compact binary as a time-varying Doppler shift. The observation of a non-zero LOS acceleration may indicate the binary is in a dense environment, such as an active
galactic nucleus (AGN) disk or
nuclear star cluster, etc. We measure the LOS acceleration of all compact binaries observed through the first part of the fourth observing run (O1-O4a) of Advanced LIGO and Virgo in addition to select binaries from later observing runs. We introduce a new method to model the LOS acceleration by directly applying the time-varying Doppler shift in the time domain to the signal produced in the binary's frame; this method can be applied to any waveform model including those with higher order modes, eccentricity, and precession. We find the LOS acceleration for all known binaries to date is consistent with zero. We find that the effects of eccentricity and LOS acceleration are partially degenerate as observed in binaries such as GW200105. Current ground-based observatories are sensitive enough to only constrain scenarios that produce high accelerations, e.g $\sim 10^{-2~}(10^{-6})~\textrm{c}/s$ for binary black hole (BBH) (binary
neutron star (BNS)) sources; however, next-generation observatories may be able to constrain the accelerations expected in some dense environments.
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Earth and Planetary Astrophysics
A study on station-keeping over irregularly shaped asteroids with different sized solar sails
Lucas Meireles, Othon Winter and Antônio Prado
Asteroid reconnaissance missions offer great contributions to a better understanding of the origins of our
Solar System and planetary defense from hazardous objects. The employment of
solar sails enable a greater number of missions and target asteroids, given it is a cheaper propulsion method. However, modeling the dynamics of
solar sails orbiting irregular gravitational fields is a challenge. And since asteroids have a wide variety of shapes and sizes, it is important to make use of a robust optimization method that allows fast adjustments to this dynamics. This study examines the use of different
solar sails and asteroid sizes for station-keeping a spacecraft orbiting an irregularly shaped asteroid. To achieve this goal, a rational
agent was developed to act as an attitude guidance system. It calculates the necessary sail orientation to keep the spacecraft near its initial orbit. The
agent uses a direct optimization strategy based on a decision tree
algorithm in order to account for a
solar sail with non-ideal reflective properties and the non-uniform gravitational field of the asteroid. By testing multiple sail sizes, this study evaluates how long the
agent may maintain the same sail orientation while still being successful at its station keeping mission. This analysis is done for different asteroid sizes and a relation between different sail and asteroid sizes is established. Results reveal a relation between sail and asteroid sizes and the attitude change frequency. Smaller sails can sustain station-keeping with fewer attitude changes. However, they are not able to achieve this goal on larger asteroids. For sufficiently small asteroids, sails smaller than those used on recent missions may be more appropriate for station-keeping. These findings suggest that current
solar sail technology is already capable of enabling successful asteroid reconnaissance missions.
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