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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 30 April

High Energy Astrophysical Phenomena

A Detailed View of the Large-Scale Sloshing Cold Front in RXJ2014.8-2430

M. J. Sundquist, S. A. Walker and M. S. Mirakhor

We analyze our new 144 ks deep Chandra observation of the sloshing cold front cluster RXJ2014.8-2430. Previous observations of RXJ2014.8-2430 with XMM-Newton shows evidence of a large scale, sloshing cold front around 800 kpc away from the cluster core. Previous shallow Chandra data also shows evidence of two younger cold fronts closer to the core. Our new deeper Chandra data allow us to analyze the fine, small scale structure of these three cold fronts. Using both beta model subtraction and Gaussian Gradient Magnitude filtering, we confirm the locations of the three cold fronts, as well as discover a large concave structure southeast of the cluster core near the outermost cold front, which could be a large Kelvin-Helmholtz instability or a gas cavity from AGN activity. Analyzing the three cold fronts, we measure the widths of the cold fronts and find them to be consistent with or lower than the Coulomb mean free paths within error, signifying that diffusion is suppressed across the cold fronts. If the concave feature is the inner rim of a cavity, we find that it has a radius in the range 200-330kpc, and would have $PV$ values in the range of $5.7 \times 10^{60}$ - $2.7 \times 10^{61}$ erg. These values would make it consistent with the some of the most powerful bubbles observed.
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Earth and Planetary Astrophysics

Smaller Than Earth Habitability Model (STEHM): The Lower Size Limit for Atmosphere Retention in the Habitable Zone

Michelle L. Hill, Stephen R. Kane, Bradford J. Foley et al. (+1 more)

With recent advances in exoplanet observational techniques enabling the discovery of increasingly smaller planets, a crucial question emerges in the search for habitable planets: how small can a planet be and still maintain an atmosphere? We present results from the Smaller Than Earth Habitability Model (STEHM) which examines how small a planet can be and still maintain a long-term (multi-gigayear) atmosphere for planets from 1.0$R_\oplus$ down to 0.5$R_\oplus$. The model is based on a stagnant lid planet orbiting within the habitable zone of a sun-like star. Our model demonstrates that planets $\geq$0.8$R_\oplus$ can maintain their atmospheres under our Earth-like default conditions for a solar analog star, while smaller planets lose their atmospheres. Variations from the default Earth-like values cause mostly minor variations to the planet size boundary results, with some changes allowing $\geq$0.7$R_\oplus$ planets to maintain their atmosphere. Initial carbon inventory emerges as the most influential parameter for atmospheric retention, though orders of magnitude difference to Earth values are required to make a significant difference to longevity of atmospheric retention. Planets with substantial initial carbon content, large amounts of heat producing elements, cool initial mantle temperatures and low core radius fractions show the best atmospheric retention capabilities. Our results indicate that atmospheric retention on small planets depends strongly on their formation conditions and early evolution, providing important constraints for future observations of rocky exoplanets and their potential habitability.
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All authors Michelle L. Hill, Stephen R. Kane, Bradford J. Foley, Laura K. Schaefer

Solar and Stellar Astrophysics · Cross-listed from physics.space-ph

Radial Dependency of ICME-associated Particle Acceleration Processes: Statistical Multipoint Observations from 2016-2023

Malik H. Walker, Robert C. Allen, George C. Ho et al. (+6 more)

During the propagation of interplanetary coronal mass ejections (ICMEs), evolution of the ICME-driven shock along with interactions with other solar wind structures, planetary bodies, and general changes to their morphology can alter particle acceleration efficiency and transport effects at their associated shocks. While the underlying mechanisms for these processes have been studied, the connection between the radial evolution of the ICME-driven shock during propagation and resulting gradual Solar Energetic Particle (SEP)and Energetic Storm Particle (ESP) intensities, composition, and acceleration has yet to be fully understood. The current distributed array of spacecraft at varying heliocentric distances provides a welcome opportunity to statistically analyze the radial dependency of particle populations and acceleration mechanisms present at ICME-driven shocks. We compile a database of 39 multipoint ICME events from 2016-2023, which are observed in situ by at least two of the following spacecraft: Parker Solar Probe (PSP), Solar Orbiter, ACE, Wind, and STEREO-A. Using the magnetic field, plasma, and ion compositional data provided by these spacecraft, we derive both local shock and ESP spectral shape parameters. By comparing the changes in these parameters at different stages of ICME propagation, we analyze the connection between the evolution of the local shock conditions and the spectral shape. We find evidence to suggest a consistent increase in shock acceleration efficiency with heliocentric distance while the parent ICME is within 0.7 au, followed by a reduction in shock efficiency at further distances.
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All authors Malik H. Walker, Robert C. Allen, George C. Ho, Glenn M. Mason, Christina M. S. Cohen, Christina Lee, Christian Möstl, Emma E. Davies, Eva Weiler

Solar and Stellar Astrophysics

EMBER: Machine-Learning Detection of Modulated Ion Acoustic Waves and Associated Core-Electron Heating in the Solar Wind with Parker Solar Probe

Argyro Sasli, Karish Seebaluck, Chris Colpitts et al. (+1 more)

Modulated ion acoustic waves (IAWs) – including triggered ion acoustic waves (TIAWs) and frequency-dispersed ion acoustic waves (FDIAWs) – are increasingly recognized as efficient drivers of electron heating in the solar wind through nonlinear wave-particle interactions. Identification of these events in the Parker Solar Probe (PSP) FIELDS burst-mode archive has so far relied on expert visual inspection and does not scale to the full mission. We present EMBER (Electron heating from Modulated Burst-mode Event Recognition), an open-source pipeline that converts PSP FIELDS Digital Burst Memory (DBM) voltage bursts into log-scaled Fourier spectrograms and applies a multi-detector, background-only anomaly detection suite. The suite combines physics-motivated detectors, classical outlier detectors, and deep learning detectors. The EMBER ensemble recovers 93% of the anomalous events at 1% FAR (1 false positive per 100 held-out backgrounds). Coincident SWEAP/SPAN diagnostics show that flagged intervals exhibit core perpendicular electron temperatures above the adiabatic cooling expectation and elevated Te/Ti, reproducing the preferential-heating phenomenology established by prior manual studies without any use of electron temperatures in the detection step.
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All authors Argyro Sasli, Karish Seebaluck, Chris Colpitts, Michael Coughlin

Earth and Planetary Astrophysics

Confirmation of Fe I on MASCARA-5 b's Dayside Observed With EXPRES

James T. Sikora, Joe Llama, Rachael M. Roettenbacher et al. (+5 more)

MASCARA-5~b/TOI-1431~b is an ultra-hot Jupiter \citep[$P_{\rm orb}=2.650237\pm0.000003\,{\rm d}$, $T_{\rm eq}=2370\pm70\,{\rm K}$, $M_{\rm p}=3.12\pm0.18\,M_{\rm Jup}$, $R_{\rm p}=1.49\pm0.05\,R_{\rm Jup}$;][]{addison2021} orbiting a bright Am star ($V=8.0\,{\rm mag}$). Recent time-series observations obtained with PEPSI@LBT during the planet's post-eclipse phases have revealed Fe~i emission lines indicative of a thermally inverted atmosphere. These observations demonstrate that MASCARA-5~b is well-suited to atmospheric characterization via emission spectroscopy, thereby motivating further follow-up observations covering additional orbital phases to constrain the planet's atmospheric chemistry, thermal structure, and dynamics. Here we present pre-eclipse time-series observations obtained with the high-resolution optical spectrograph EXPRES@LDT. Our analysis confirms the previous detection of gas-phase Fe~i on MASCARA-5~b's dayside (with a $5.5\sigma$ significance obtained from two nights of observations) and the fact that the thermal profile is inverted with lower and upper temperatures $\sim2000\,{\rm K}$ and $\sim4500\,{\rm K}$, respectively. A search for Fe~ii and Cr~i did not yield any plausible detections. We also find that the pre-eclipse signal exhibits a non-negligible blueshift of $-3.2\pm1.4\,{\rm km/s}$ potentially caused by winds.
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All authors James T. Sikora, Joe Llama, Rachael M. Roettenbacher, Elisabeth M. Brann, Jean-Michel Désert, Alex S. Polanski, Malena Rice, Lily Zhao

Instrumentation and Methods for Astrophysics

Radiation Total Dose for PRIMA: Cold Exposure with Alpha Particles

Elijah Kane, Chris Albert, Andrew Beyer et al. (+9 more)

The Probe far-Infrared Mission for Astrophysics (PRIMA) is a far-infrared (24-261 micron wavelengths) probe-class space observatory currently under Phase A study, which promises orders-of-magnitude improvement in mapping speed over its predecessors. PRIMA will field exquisitely sensitive kilopixel arrays of kinetic inductance detectors (KIDs) for the Far-Infrared Enhanced Survey Spectrometer (FIRESS) instrument. PRIMA will orbit in space at the Sun-Earth L2 point, where Planck found the energetic particle flux to be about 300/min/cm2. Thus, the possible effect of a high fluence of energetic particles on the detector sensitivity must be characterized. Previous work has suggested that bombardment of KIDs by ions can reduce the quasiparticle lifetime (Barends et. al. 2009), but the conditions of the experiment were not representative of a detector which is continuously held at sub-Kelvin temperatures in the energetic particle environment of L2 orbit. To better replicate the damage which would be produced by energetic particles in this environment, we developed a fully cryogenic irradiation experiment in which a stepper motor controls a screen which can block or reveal an alpha particle emitter. This setup can be used to irradiate aluminum KID arrays fabricated for FIRESS to well-controlled dose levels. In this work, we calculate the damage dose expected for a 5-year mission in L2 orbit, and we irradiate an array to approximately 62 percent of this level. Before and after irradiation, we measure the quasiparticle lifetimes, resonant frequencies, and quality factors of the detectors.
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All authors Elijah Kane, Chris Albert, Andrew Beyer, Charles Bradford, Pierre Echternach, Logan Foote, Jason Glenn, Henry LeDuc, Hien Nguyen, Thomas Stevenson, Brian Zhu, Jonas Zmuidzinas

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

Merger remnant and eccentricity dynamics surrogates for eccentric nonspinning black hole binaries

Adhrit Ravichandran, Peter James Nee, Keefe Mitman et al. (+22 more)

Accurate models of merger remnants are increasingly important for gravitational-wave science, including precision tests of gravity with ringdown, inference of black-hole populations, and modeling hierarchical mergers. For eccentric binaries, remnant mass, spin, and recoil carry nontrivial imprints of eccentricity that are both physically informative and more challenging to model, yet remain less developed than in the quasi-circular case. We present two new models trained on numerical-relativity (NR) simulations of unequal-mass, non-spinning eccentric binary black holes: NRSurE_q4NoSpin_Remnant, which predicts remnant properties, and NRSurE_q4NoSpin_Dynamics, a time-domain surrogate for the evolution of eccentricity and mean anomaly. Both models are trained on NR simulations over a three-dimensional parameter space with mass ratios $q \leq 4$, eccentricity $e < 0.23$, and mean anomaly $\ell \in [0,2\pi)$ radians, where both $e$ and $\ell$ defined at $t=-1000M$ relative to peak amplitude and $M$ is the total mass. We highlight some applications, including the phenomenological impact of eccentricity on remnant properties and the enhancement or suppression of recoil. We also provide error estimates for all modeled quantities, supporting reliable use in current and future gravitational-wave parameter-estimation analyses. Both models will be made available through open-source codes.
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All authors Adhrit Ravichandran, Peter James Nee, Keefe Mitman, Tousif Islam, Scott E. Field, Vijay Varma, Michael Boyle, Andrea Ceja, Nils Deppe, Noora Ghadiri, Lawrence E. Kidder, Prayush Kumar, Marlo Morales, Jordan Moxon, Kyle C. Nelli, Harald P. Pfeiffer, Antoni Ramos-Buades, Katie Rink, Hannes R. Rüter, Mark A Scheel, Md Arif Shaikh, Leo C. Stein, Daniel Tellez, William Throwe, Nils L. Vu

Cosmology and Nongalactic Astrophysics

Towards a measurement of the primordial helium isotope ratio

Ryan J. Cooke, James W. Johnson, Pasquier Noterdaeme et al. (+4 more)

We report the discovery of two metastable neutral helium (He I*) absorbers in the Milky Way, and use the upgraded CRyogenic InfraRed Echelle Spectrograph on the Very Large Telescope to determine the helium isotope ratio, $^{3}$He/$^{4}$He, along these sightlines. We have also obtained deeper observations of a third sightline to report a $\lesssim4\%$ precision measure of $^{3}$He/$^{4}$He in the Orion Nebula. These data have allowed us to place a $2\sigma$ limit on the time-variability of He I* absorption in the Orion nebula, ${\rm d}\log_{10} [N({\rm He\,I}^{*})/{\rm cm}^{-2}]/{\rm d}t\leq7.2\times10^{-4}~{\rm dex~yr}^{-1}$ ($<0.17\%~{\rm yr}^{-1}$), suggesting that these absorbers are in radiative equilibrium. We compute new galactic chemical evolution models of the Milky Way, and use our observations to infer the primordial helium isotope ratio and a scaling factor for the yields reported by nucleosynthesis calculations. Based on the data and models that we report here, we infer a best-fit value ($^{3}$He/$^{4}$He)$_{\rm P}=(1.15^{+0.24}_{-0.21})\times10^{-4}$, which agrees with Big Bang nucleosynthesis calculations that assume the Standard Model of particle physics in combination with the baryon density inferred from the cosmic microwave background temperature fluctuations. We infer the stellar yield scale relative to the solar metallicity, $y/Z_{\odot}=2.12^{+0.31}_{-0.29}$, which is somewhat higher than previously found. Finally, we note that the forthcoming extremely large telescopes are poised to determine $^{3}$He/$^{4}$He in more metal-poor environments, to secure a model-independent determination of the primordial value.
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All authors Ryan J. Cooke, James W. Johnson, Pasquier Noterdaeme, Max Pettini, Louise Welsh, Aldric Wong, Celine Peroux

Cosmology and Nongalactic Astrophysics

Deep Learning galaxy cluster's structural parameters from Weak Lensing observations

M. Fogliardi, M. Meneghetti, C. Giocoli et al. (+6 more)

Galaxy clusters are the most massive gravitationally bound structures in the Universe and key probes of cosmic evolution. The large data volume expected from upcoming surveys requires efficient automated analysis methods for tens of thousands of clusters. We present a study using Convolutional Neural Networks (CNNs) to infer cluster structural parameters from weak gravitational lensing observations. Three architectures (VGG-Net, Inception-v4, Inception-ResNet-v2) were implemented in PyTorch and trained on 75,000 synthetic reduced shear maps generated with MOKA, simulating galaxy clusters at $z = 0.25$. The networks simultaneously predict five parameters: virial mass, NFW concentrations, substructure count, and smooth component mass fraction. Tests on 5000 clusters show high accuracy for primary properties. With realistic noise ($n_{\rm gal}=30$, $\sigma_{\epsilon}=0.3$), mass predictions remain robust (RMS $\sim 1.02 \times 10^{14}$ M$_\odot$/h, $\sim20$% deviation). Concentration estimates are stable, with VGG-22 achieving the lowest RMS. Substructure count properties are more challenging, with systematic underestimation across models, while the smooth component mass fraction is consistently well recovered, indicating strong robustness against noise. Comparison with traditional shear profile fitting shows improved CNN performance. VGG-22 achieves near-unbiased mass estimates and significantly better concentration recovery, reducing systematic errors. These results demonstrate that CNNs provide an effective and scalable alternative to traditional methods, particularly suited for large survey datasets.[Abridged]
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All authors M. Fogliardi, M. Meneghetti, C. Giocoli, L. Moscardini, P. Rosati, L. Leuzzi, G. Angora, L. Bazzanini, C. Spinelli

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

Pre-inflationary QCD axion stars after moduli domination

Edward Hardy, Noelia Sánchez González, Henry Stubbs et al. (+1 more)

The growth of adiabatic density perturbations during an era of early matter domination induces $\mathcal{O}(1)$ fluctuations in pre-inflationary QCD axion dark matter across a broad, string-theory-motivated parameter space. Remarkably, at $\Lambda$CDM matter-radiation equality the scale of these perturbations coincides with the quantum Jeans scale, so they collapse to solitonic “axion stars”. These axion stars have densities up to $10^4\,\mathrm{eV}^4$, and, including their surrounding halos, they contain as much as $50\%$ of dark matter. Direct searches for a smooth axion background can be suppressed, but transient enhancements or indirect astrophysical signals at axion masses $m_a\lesssim 10^{-5}\,{\rm eV}$ would point to a non-standard cosmological history.
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All authors Edward Hardy, Noelia Sánchez González, Henry Stubbs, Lorenzo Tranchedone

Solar and Stellar Astrophysics

Self-consistent numerical simulations for the formation and dynamics of solar prominences

Lisa-Marie Zessner, Robert H. Cameron, Sami K. Solanki et al. (+1 more)

Solar prominences are cool and dense plasma structures floating in the hot solar corona. They are ubiquitous features in the solar atmosphere, but their formation mechanism is still unclear. Here we perform comprehensive fully three-dimensional numerical simulations of prominence formation including the physics necessary to describe all atmospheric layers of the sun. With appropriate initial conditions for the magnetic field, solar prominences form self-consistently in the simulations. The formation starts by the random ejection of a dense plasma seed from the chromosphere into the corona. Subsequently, the prominence is built up by a combination of plasma injections from the chromosphere and condensation of inflowing coronal plasma. The prominence properties qualitatively match those of observed prominences. Our findings demonstrate the importance of the dynamics at and below the solar surface in the formation and evolution of solar prominences. This suggests that subsurface dynamics should also be considered in the study of prominence eruptions, which can be associated with coronal mass ejections.
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All authors Lisa-Marie Zessner, Robert H. Cameron, Sami K. Solanki, Damien Przybylski

Earth and Planetary Astrophysics

The dark and featureless surface of rocky exoplanet LHS 3844 b from JWST mid-infrared spectroscopy

Sebastian Zieba, Laura Kreidberg, Brandon P. Coy et al. (+13 more)

JWST has opened a new era in the study of rocky exoplanets, enabling direct characterization of their surfaces with mid-infrared spectroscopy. Different types of rock have distinct spectral features that are diagnostic of the chemical composition and other physical properties like surface texture. Measurements of these features can provide valuable clues about a planet's geologic history and interior processes. Here we report a JWST 5-12 micron thermal emission spectrum for the rocky exoplanet LHS 3844 b. It is best matched by a dark, low-silica surface, such as basalt or other olivine-rich materials. The spectrum rules out fresh powder surfaces; however, space weathering can darken the powders and make them more consistent with the data. The data also disfavor trace concentrations of CO$_2$ or SO$_2$ gas (with 5-sigma and 3-sigma upper limits of 100 mbar and 10 microbar, respectively). Taken together, these results are well fit by an old, space-weathered surface with no evidence of accumulated volcanic gases.
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All authors Sebastian Zieba, Laura Kreidberg, Brandon P. Coy, Aaron Bello-Arufe, Kimberly Paragas, Xintong Lyu, Renyu Hu, Aishwarya Iyer, Edwin S. Kite, Daniel D.B. Koll, Kay Wohlfarth, Emerson Whittaker, Heather Knutson, Robin Wordsworth, Caroline Morley, Laura Schaefer

Cosmology and Nongalactic Astrophysics

A New Robust Constraint on the Self-interaction Cross-section of Dark Matter with Double Radio Relic Clusters

M. James Jee, Dongak Park and Wonki Lee

Merging galaxy clusters are a promising laboratory for measuring the self-interaction cross-section (SICS) of dark matter. However, previous studies have focused on galaxy-mass offsets, which numerical simulations have shown to be intrinsically small because galaxies remain tightly coupled to the dominant dark matter potential even with significant self-interaction. Their interpretation is further complicated by unknowns of the merger phase, geometry, and initial conditions. In this paper, we overcome these obstacles by introducing the shock-to-shock distance, traced by double radio relics, as a merger chronometer that time-stamps the post-pericenter dynamical phase. Because the propagation speed of merger shocks is nearly independent of the SICS, while the halo-to-halo distance is depressed by SIDM-induced drag, the ratio of the two distances translates directly into a constraint on sigma/m. Applying this method to a gold sample of eleven cluster mergers hosting symmetric double radio relics, we determine an upper limit on the SICS of sigma/m < 0.22 (0.63) cm^2/g at the 68% (95%) confidence level. This is the first constraint from cluster collisions that fully marginalizes over mass uncertainty, viewing angle, collision speed, merger phase, impact parameter, and gas profile slope.
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Astrophysics of Galaxies

The LISA Astrophysics MBHcatalogues Project: A comparison of predictions of simulated massive black hole binaries

David Izquierdo-Villalba, Melanie Habouzit, Matteo Bonetti et al. (+67 more)

In the hierarchical paradigm of galaxy formation, central massive black holes (MBHs) are expected to coalesce after the merger of their host galaxies. One of the main goals of the Laser Interferometer Space Antenna (LISA) is to constrain the origin and growth of MBHs through their merger rates and mass distribution. Predicting MBH merger rates requires not only tracing their statistical population from large to small physical scales (kpc to sub-pc) but also modelling their formation, accretion, dynamics, mergers, and their galactic physical processes across cosmic time. This project is the result of a large collaborative effort undertaken by the LISA Astrophysics Working Group, bringing together its collective expertise on MBH formation, evolution, and modelling, to build a comprehensive understanding of MBH merger rates across cosmic time. The project compares various theoretical predictions of MBH merger rates, quantifies the spread, and evaluates the global astrophysical uncertainties of the LISA event rates. To build a unique and complete view, our work is based on about 20 semi-analytical models and cosmological simulations from the literature, all employing distinct approaches to modelling MBH and galaxy physics. To compute the merger rates, we also incorporate delays arising from the dynamical phase of MBH hardening to coalescence. We present the expected LISA merger rates given current galaxy formation models and discuss how the merger rate depends on model assumptions, such as the seeding model and the resolution of cosmological simulations.
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All authors David Izquierdo-Villalba, Melanie Habouzit, Matteo Bonetti, Silvia Bonoli, Alessia Gualandris, Marta Volonteri, Federico Angeloni, Enrico Barausse, Aklant Bhowmick, Laura Blecha, Alexander Bonilla Rivera, Elisa Bortolas, Mesut Caliskan, Pedro R. Capelo, Ana Caramete, Laurentiu Caramete, Nianyi Chen, Monica Colpi, Thierry Contini, Romeel Davé, Pratika Dayal, Colin DeGraf, Roger Deane, Roberto Decarli, Rémi Delpech, Tiziana Di Matteo, Chi An Dong Páez, Alister W. Graham, Daryl Haggard, Dimitrios Irodotou, Peter H. Johansson, Atte Keitaanranta, Luke Zoltan Kelley, Fazeel Mahmood Khan, Vivienne Langen, Kunyang Li, Shihong Liao, Alberto Mangiagli, Sylvain Marsat, Joe McCaffrey, Yueying Ni, Coral Pillay, Florentina-Crenguta Pislan, Alex Rawlings, John Regan, Bastián Reinoso, Jaelyn Roth, Milton Ruiz, Olga Sergijenko, Alberto Sesana, Golam Shaifullah, Jasbir Singh, Daniele Spinoso, Alexandre Toubiana, Michael Tremmel, Alessandro Trinca, Rosa Valiante, Yihao Zhou, Yohan Dubois, Luca Graziani, Christopher C. Lovell, Sebastien Peirani, William J. Roper, Joop Schaye, Raffaella Schneider, Maxime Trebitsch, Aswin Vijayan, Mark Vogelsberger, Stephen Wilkins, John Wise

Astrophysics of Galaxies

Chemical Taxonomy of $\omega$~Centauri: Ten Populations Reveal a Multi-Phase Enrichment History

Furkan Akbaba, Olcay Plevne, Timur Şahin et al. (+1 more)

$\omega$~Centauri, the most massive globular cluster in the Milky Way, exhibits a level of stellar population complexity that has long resisted a unified chemical characterisation. We exploit high-resolution near-infrared spectroscopy from the Milky Way Mapper survey (MWM DR19) to construct one of the largest homogeneously analysed samples of $\omega$~Cen members to date. Applying Ward-linkage hierarchical clustering in a seven-dimensional chemical abundance space, without prior assumptions on population number or boundaries, we identify ten chemically distinct stellar populations. Their nucleosynthetic signatures trace four enrichment channels: iron-peak, $\alpha$-element, CNO-cycle, and high-temperature proton-capture processes. The populations organise into two dominant groups separated by a large light-element spread at a modest iron baseline, consistent with AGB-driven self-enrichment. This dichotomy reflects distinct enrichment pathways: core-collapse supernovae establish the iron baseline, while AGB stars dominate light-element and $s$-process enrichment. A decoupled rise in $s$-process abundances relative to iron-peak elements, together with sub-dominant Type~Ia contributions across all metallicities, indicates evolution on timescales shorter than the characteristic Type~Ia delay time. One intermediate-metallicity population retains a primordial composition, providing evidence for spatially segregated enrichment within the progenitor. The most metal-rich component may trace star formation continuing after accretion into the Milky Way halo. All populations lie in the accreted regime of the $[\mathrm{Al/Fe}]$–$[\mathrm{Mg/Mn}]$ plane, supporting an ex-situ origin. These results reinforce the interpretation of $\omega$~Cen as the remnant nucleus of an accreted dwarf galaxy and provide a framework for future chemo-dynamical studies.
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All authors Furkan Akbaba, Olcay Plevne, Timur Şahin, Sena Aleyna Şentürk

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

Beyond the Separatrix: Analytic Continuation of Darwin Variables for Plunging Geodesics in Schwarzschild Spacetime

Francisco M. Blanco

We study geodesic motion of a test particle in Schwarzschild spacetime. Bound and scattering geodesics are commonly described using Darwin variables, which provide a convenient parametrization of the radial motion. However, this description breaks down at the separatrix and does not extend straightforwardly to plunging trajectories. We construct an analytic continuation of Darwin variables that yields a real parametrization of bound, scattering, and plunging Schwarzschild geodesics, thereby providing a unified kinematical description of all types of test-mass motion. As a proof of concept, we then apply these variables to a simple non-geodesic evolution in which the energy and angular momentum are driven by a constant external force. This toy model is not intended to represent a physical radiation-reaction model, but rather to illustrate how the extended variables can be used to follow an orbit through a transition to plunge using a single orbital phase variable across the separatrix.
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Earth and Planetary Astrophysics

The Influences of Hydrogen-Silicate-Iron Miscibility on the Demographics of Sub-Neptunes and Super-Earths

Edward D. Young and Aaron Werlen

Models based on variable miscibility among hydrogen, molten silicate, and molten iron, coupled with atmospheric escape, can reproduce the observed occurrence density structure of sub-Neptunes and super-Earths in mass-radius space. The models are also consistent with the radius gap and the observed radius-period relationship exhibited by these planets. The degree of overlap between predicted and observed planetary occurrences suggests that hydrogen-silicate-iron miscibility may serve as a unifying concept for the formation and evolution of these planet classes. The well-defined equilibrium conditions at the boundary between supercritical magma oceans and the overlying hydrogen-rich envelopes are important features of the models. Planets formed with less than ~1 % hydrogen by mass develop discrete, terrestrial-like metallic cores, while those accreting greater hydrogen concentrations are predicted to have fully miscible interiors and no discrete metal cores. Hydrogen-silicate-iron miscibility provides an overarching explanation for the full range of sub-Neptune and super-Earth architectures based on the accreted hydrogen mass fraction and the phase equilibria governing silicate, iron metal, and H$_2$ miscibility.
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Cosmology and Nongalactic Astrophysics

Identifying the host of compact binary mergers

Alberto Salvarese, Hsin-Yu Chen and Daniel E. Holz

Finding the host galaxies of stellar-mass compact binary mergers will open a new window for studying their formation histories and measuring key cosmological parameters, such as the Hubble constant. To date, only one merger, GW170817, has had its host galaxy confidently identified through electromagnetic counterpart observations. The large localization volumes from the LIGO-Virgo-KAGRA (LVK) network, combined with the lack of electromagnetic emission for most events, make host identification challenging. However, as the sensitivity of the gravitational-wave (GW) detector network improves, events are becoming increasingly well localized. Furthermore, galaxy luminosity traces mass or star formation rate, and thus correlates with the probability of hosting a merger. Focusing on the most luminous galaxies within the localization volumes of the best-localized GW events, we estimate the corresponding Hubble constant for each galaxy by combining its redshift with the luminosity distance inferred from LVK observations. For the well-localized LVK events S250207bg, GW190814, and S250830bp, we find only $1$, $1$, and $4$ galaxies, respectively, when restricting the analysis to the most luminous $1\%$ of galaxies above $L_{\rm th} \sim 10^{9} h^{-2} L_{\odot}$ in each event's localization volume and adopting a broad $H_0$ prior. The probability of these galaxies being random, and not associated with the GW events, is $29$-$36\%$ across the three events. We encourage further follow-up observations of these candidate host galaxies. We expect this approach to become increasingly powerful in future LVK observing runs, enabling constraints on merger formation histories and measurements of the Hubble constant.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

New gravitational-wave templates for metastable cosmic strings: Loop breaking versus network collapse

Doa Hashemi Asl and Kai Schmitz

Metastable cosmic strings are a common prediction of grand unified theories and act as a source of a gravitational-wave background (GWB) that can explain the 2023 pulsar timing array (PTA) signal. In this paper, we revisit the GWB signal from metastable strings, emphasizing the need to carefully distinguish between two different time scales: (i) t_LB, the time scale of loop breaking because of spontaneous monopole nucleation on closed string loops, and (ii) t_NC, the time scale of network collapse when string segments attached to monopoles begin to enter the Hubble horizon. We discuss under which conditions these two time scales are similar or far apart from each other and illustrate the resulting consequences for the GWB signal. In doing so, we generalize the description of the GWB signal from metastable strings to a three-parameter model in terms of the string tension G\mu and the time scales t_LB and t_NC, which allows us to unify the modeling of standard metastable strings with what is known as quasi-stable strings. In the limit of a large t_LB/t_NC ratio, we, moreover, derive a compact analytical expression for the predicted GWB spectrum in excellent agreement with numerical results in the literature. We thus conclude that our new templates for the GWB spectrum from metastable strings can be readily used in the analysis of future PTA data sets.
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High Energy Astrophysical Phenomena

The faint voice of a radio-weak BL Lacertae: modeling the broadband emission of WISE~J141046.00+740511.2

A. M. Carulli, F. L. Vieyro, M. M. Reynoso et al. (+2 more)

The WISE source, J141046.00+740511.2, has been recently observed from radio to $\gamma$ rays. Although the optical spectrum is consistent with a BL Lacertae (BL Lac) object, the source displays unusually weak radio emission, which challenges standard interpretations. Our aim is to understand the origin of the broadband emission from J141046.00+740511.2, using a leptonic model of an extended jet. To obtain the distribution of electrons along the conical jet, we solved a steady-state convective transport equation. Emissivities were computed along the jet and integrated over the cone volume to obtain the observed flux. Our model successfully reproduces the observed multiwavelength spectral energy distribution from radio to $\gamma$ rays and naturally accounts for the source's low radio flux without invoking extra emission zones. We also reproduce the mid-IR emission within the same framework. These results demonstrate that extended jet leptonic models can robustly describe the broadband physics of radio-weak BL Lacs.
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All authors A. M. Carulli, F. L. Vieyro, M. M. Reynoso, E. J. Marchesini, I. Andruchow

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Semi-analytic bounds on axion-like-particle supernovae emission

Ana Luisa Foguel and Eduardo S. Fraga

Core-collapse supernovae provide natural laboratories for the production of new light particles. In particular, axion-like particles (ALPs) can be constrained via SN1987A cooling arguments. However, significant astrophysical and nuclear uncertainties imply that such bounds may vary strongly depending on modeling choices, even when expensive simulations are employed. In this context, semi-analytic methods offer a simple and fast alternative for deriving new-physics constraints. Building on a previous semi-analytic framework, in which proto-neutron star (PNS) observables are expressed in terms of six global PNS parameters, we include a finite ALP mass in the calculation and derive bounds in the axion-nucleon coupling versus mass plane. The obtained bounds are in good agreement with previous results from numerical simulations, demonstrating the robustness of the method. We also illustrate the sensitivity of the bounds to different PNS parameter calibrations, nuclear effects and cooling exclusion criteria.
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Cosmology and Nongalactic Astrophysics

Cosmological intercept tension

Jia-Qi Wang and Shao-Jiang Wang

The long-standing tension in the Hubble constant $H_0$ has motivated extensive explorations of both new physics and observational systematics, for example, the late-time systematics in measuring the B-band absolute magnitude $M_B$ of type Ia supernovae, which is degenerated with $H_0$ via an intercept $-5a_B=M_B+5\lg (c/H_0/\mathrm{Mpc})+25$ in the linear relation $m_B=5\lg d_L(z)-5a_B$ between the apparent magnitude $m_B$ and logarithmic dimensionless luminosity distance $\lg d_L(z)$. Therefore, this intercept can be evaluated directly from pure observational quantities ($m_B$ and the redshift $z$) for a given model of $d_L(z)$ without knowing underlying systematics in $M_B$-$H_0$ degeneracy. Hence, the constancy of this intercept across different supernova datasets and different redshift bins within the same dataset for a given late-time model serves as a powerful diagnostic for disentangling late-time new physics from local supernova systematics. In this mini-review, we will show that: (1) there is a local $a_B$ tension in PantheonPlus around $z\sim0.01$, and the elimination of it leads to a $H_0$ measurement consistent with both SH0ES typical three-rung and first two-rung measurements; (2) there is a late-time $a_B$ tension in DES-Y5 around $z\sim0.1$, and the elimination of it largely reduces the preference for dynamical dark energy. We also update the late-time $a_B$-tension analysis for both DES-Y5 and DES-Dovekie supernovae, and find that this $a_B$ tension around $z\sim0.1$ is mainly driven by the inter-data tension between DES supernovae and DESI+Planck constraint, and the dynamical dark energy is preferred as a compromise of this tension. Finally, we briefly mention an interacting dark energy model that resolves this tension among DES, DESI, and Planck, and point out a crucial difference between the effective and apparent equations of state of dark energy.
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High Energy Astrophysical Phenomena

On the polarization position angle jumps in FRB 20240114A

Ninisha Manaswini, Danté M. Hewitt, Laura G. Spitler et al. (+6 more)

Fast radio bursts (FRBs), thought to originate from magnetars, exhibit diverse polarization properties that constrain their emission physics and local magneto-ionic environments. The polarization position angle (PPA) is particularly sensitive to magnetic-field geometry in the emitting region and propagation effects in the magnetosphere and beyond. In hyper-active repeaters, PPAs are typically stable within bursts and over timescales of hours to days. Here, we present observations of the repeating source FRB~20240114A, which show significant burst-to-burst PPA variations. Using full-Stokes, high-time-resolution observations from the Nançay Radio Telescope (1.1–1.8\,GHz) and the Effelsberg 100-m telescope (1.3–1.5\,GHz) over $\sim1$~year, we measure rotation measures (RMs), polarization fractions, and time-resolved PPAs across 12 epochs. The RMs remain stable, and the emission is predominantly highly linearly polarized, with $\sim81\%$ of bursts showing $L/I > 0.8$, while circular polarization is weaker ($\sim16\%$ with $|V/I| > 0.1$). We find no evidence for Faraday conversion. The PPA exhibits rapid, stochastic variations from milliseconds to hours, spanning $\pm90^\circ$ during two active periods and $\pm50^\circ$ in a third. The distribution of PPA jumps shows that (1) there is no difference in the distribution of jumps on timescales shorter or longer than 1\,s; (2) positive and negative jumps are equally likely; and (3) a jump of $\pm90^\circ$, as expected from, e.g., orthogonal mode jumps, is not more common than any other value. This combination of stable RM, high linear polarization, and extreme PPA variability is not seen in other hyper-active repeaters. These results disfavor emission from a single fixed region and instead suggest multiple emission regions and/or strong magnetospheric and foreground propagation effects, such as plasma lensing.
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All authors Ninisha Manaswini, Danté M. Hewitt, Laura G. Spitler, Jason W. T. Hessels, Ramesh Karuppusamy, Jeff Huang, Pranav Limaye, Lucas Guillemot, Ismaël Cognard

High Energy Astrophysical Phenomena

A common four-beam geometry reveals altitude-stratified GeV pulses in canonical young pulsars

Paul K. H. Yeung and Takayuki Saito

Despite the diversity and energy dependence of $\gamma$-ray pulse morphologies in Crab, Vela and Dragonfly, the phaseograms of these three canonical young pulsars can be organised within a single four-beam geometric template. Using Fermi Large Area Telescope data, we fit the 60~MeV–3~GeV phaseograms with a mechanism-agnostic, geometry-first parametric model that incorporates phase-dependent Doppler shifts and constrains the three-dimensional locations and bulk motions of four emission sites. In each pulsar, the phaseogram admits a decomposition into two altitude-separated beam pairs. The lower-altitude pair is produced by plasma with bulk motion close to azimuthal corotation, sharpening the main peaks. The higher-altitude pair shows a radially outward bulk-motion component, suggestive of inertial effects in a toroidally dominated magnetic field, and contributes bridge/shoulder emission and ripple-like modulations overlapping the main peaks. As a posteriori, the lower-altitude pair is consistent with curvature-dominated outer-magnetospheric emission, while the higher-altitude pair is consistent with synchrotron-dominated emission from a current-sheet-like outflow. Higher-altitude site heights vary from $\simeq 0.7$ (Crab, $\approx 1$~kyr) to $\simeq 1.1$–$1.4$ light-cylinder radii (Vela and Dragonfly, $\approx 10$~kyr). This unified four-beam, observation-driven geometry maps an altitude-dependent azimuthal tilt of pulsed $\gamma$-ray emission, providing an observationally anchored framework amenable to systematic tests and readily extensible to other young pulsars.
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Astrophysics of Galaxies

Applications of 1.4 GHz diagnostics to Type Ia Supernova host galaxies

S. Ramaiya, M. J. Jarvis, M. Vincenzi et al. (+2 more)

Type Ia supernova (SN Ia) standardisation parameters exhibit evidence for systematic variation across the host galaxy star-formation rate - stellar mass (SFR$-M_\star$) plane, motivating the incorporation of galaxy SFR information in cosmological inference. SFRs are commonly estimated via spectral energy distribution (SED) fitting with far-infrared (FIR) measurements to account for dust-obscured star formation. Such FIR coverage will, however, be limited for upcoming time-domain surveys such as the Rubin Observatory Legacy Survey of Space and Time (LSST), necessitating the use of alternative SFR tracers. Here, we reconstruct the SFR - $M_\star$ plane using 1.4 GHz diagnostics, to test the consistency of host classifications against FIR-constrained SED-based estimates. Within this plane, SN Ia host galaxies are divided into three regions: Region 1 (low-mass), Region 2 (high-mass star-forming) and Region 3 (high-mass passive). We find that ${\sim}84$ per cent of SN hosts retain identical region assignments when using radio versus FIR-constrained SED-derived SFRs. Measuring SN Ia nuisance parameters ($\alpha,\beta, M$) within each subregion, we find consistent values between the two SFR - $M_\star$ plane reconstructions, indicating limited sensitivity to SFR estimator choice, with the largest deviations in Region 3 at ${\sim}1.1\sigma$. Across the three 1.4 GHz SFR - $M_\star$ subregions, we confirm the region-dependent variation in SN Ia standardisation parameters - particularly $\beta$ - reported in our earlier SED-based analysis. With near-complete radio coverage of the LSST footprint anticipated from current and forthcoming radio continuum surveys (e.g., Square Kilometre Array), radio SFR calibrations will become an increasingly useful and scalable approach to host galaxy classification, supporting the construction of robust SN Ia subsamples for precision cosmology.
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All authors S. Ramaiya, M. J. Jarvis, M. Vincenzi, M. Sullivan, I. H. Whittam

Solar and Stellar Astrophysics · Cross-listed from gr-qc

Rotation-Induced Effective Anisotropy in White Dwarfs as a Newtonian Benchmark with Relativistic Scale Assessment

Aray Muratkhan, Aliya Taukenova, Saken Toktarbay et al. (+1 more)

We develop a one-dimensional Newtonian reduction for uniformly rotating cold white dwarfs in which the angle-averaged centrifugal support is represented by an effective anisotropic term. From the stationary Euler equation, using \(\langle\sin^2\theta\rangle=2/3\), the rotational contribution becomes $ \Delta_{\rm rot}(r)=\frac{1}{3}\rho(r)\Omega^2 r^2 . $ The mapping keeps the spin frequency explicit while preserving a one-dimensional hydrostatic system. With the Chandrasekhar degenerate-electron equation of state, we compute sequences over \(\rho_c\in[10^6,10^{11}]~{\rm g\,cm^{-3}}\) for rotation proxies \(f=\Omega/\Omega_{K,0}(\rho_c)\leq0.35\). The high-density readout shows monotonic increases of mass and radius with \(f\), with a percent-level mass shift for the largest retained proxy. Applicability is checked on the rotating configurations through sub-Keplerian diagnostics and the bulk-interior measure \(\mathcal{A}_{10^{-2}}\). We further compare the reduced rotational correction with an auxiliary quasi-two-dimensional reconstruction and a static isotropic Tolman–Oppenheimer–Volkoff reference sequence. These scale checks show that the reduced model remains useful for controlled trend-level surveys in the slow-rotation regime, while rotational and static relativistic corrections can both become percent-level effects at high central density. The construction provides a transparent Newtonian benchmark for future axisymmetric and relativistic rotating white-dwarf calculations.
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All authors Aray Muratkhan, Aliya Taukenova, Saken Toktarbay, Hernando Quevedo

Cosmology and Nongalactic Astrophysics

Axion dark matter from extended misalignment with a constant-$\omega_\phi$ pre-oscillatory phase and dark radiation

José María Pérez-Poyatos

In this work, we extend the standard pre-inflationary misalignment mechanism for axion-like particles (ALPs) by introducing a pre-oscillatory phase with constant equation of state $\omega_\phi\in[-1,1]$, generated by a tracking potential. During the radiation-dominated era, the potential undergoes a rapid transition to the conventional cosine potential. The resulting change in the potential energy across the transition can drive the ALP into a kinetic misalignment phase ($\omega_\phi=1$) prior to the onset of oscillations. Motivated by persistent cosmological tensions, such as those in $H_0$ and $S_8$, we also investigate an ALP coupling to a dark radiation sector (DR), allowing for its decay. Using a Bayesian analysis, we constrain the ALP parameter space with current cosmological data. Our analysis shows that ALP-induced DR does not resolve the existing tensions. Instead, the data place robust constraints on the model, favoring negative values of $\omega_\phi$ and constraining the symmetry-breaking scale to $f_\phi\in[80,1.5\times10^{10}]~\mathrm{TeV}$, corresponding to ALP masses in the range $m_\phi\in[10^{-20},10^{-2}]~\mathrm{eV}$.
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Solar and Stellar Astrophysics

Pulsation-driven helium transport as a potential source of the Blazhko effect

Geza Kovacs

We present a highly simplified nonlinear hydrodynamical model to emulate the main observed features of amplitude modulation (commonly known as Blazhko effect) in RR Lyrae stars. The model is based on the assumption that the periodic flow generated by the pulsation carries surplus helium in the ionization zones He I and II. Once this extra helium reaches a critical amount, a Rayleigh-Taylor-type instability leads to a back-flow of the surplus helium and the process starts over again, due to the continuing effect of pumping helium upward by the pulsation. This periodic variation of helium leads to various efficiency of radiation flux blocking in the helium ionization zone that shows up as a long-term periodic variation of the pulsation amplitude.
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Instrumentation and Methods for Astrophysics

The Large Array Survey Telescope-Pipeline. II. Image Subtraction and Transient Detection

R. Konno, E. O. Ofek, A. Krassilchtchikov et al. (+16 more)

Context. The Large Array Survey Telescope (LAST) is a wide-field visual-band survey designed to explore the variable and transient sky with high cadence. Its raw data stream is automatically processed in near real time at the observatory site, producing science-quality images, catalogs, and transient alerts. Transient alerts are then reported to the Transient Name Server (TNS). Aims. The LAST pipeline comprises two major components: (i) processing and calibration of single images followed by coaddition of $20\times20$s exposures, producing single-image and coadded-image catalogs; and (ii) subtraction of coadded images from calibrated reference images followed by transient detection. In this work we present a detailed description and validation of the second component of the pipeline. Methods. Transient detection is based on the algorithm for proper image subtraction (ZOGY). We combine ZOGY subtraction with the Translient statistic for sub-pixel motion discrimination, together with a sequence of deterministic filtering steps, to produce a clean stream of transient candidates without the use of machine learning. Results. Using commissioning data, the pipeline achieves a preliminary $5\sigma$ limiting magnitude of $20.3$-$20.7$mag, a single-epoch transient detection efficiency of $\sim80$%, and a purity of $\gtrsim90$% at signal-to-noise ratio of $\geq7.5\sigma$.
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All authors R. Konno, E. O. Ofek, A. Krassilchtchikov, Y. Shvartzvald, S. Ben-Ami, D. Polishook, C. Tishler, E. Segre, S. Garrappa, E. A. Zimmermann, A. Horowicz, P. Chen, A. Gal-Yam, M. Engel, Y. M. Shani, S. A. Spitzer, S. Fainer, O. Yaron, A. Blumenzweig

Cosmology and Nongalactic Astrophysics

The Complex Structure of the Abell 548 - Abell 3367 Region

Mark J. Henriksen and Layla Ahmed

Archival XMM and ROSAT X-ray data are used to investigate the structure of the Abell 548 - Abell 3367 region. Based on previous optical studies, this is a region likely to be rich in structure though studies are in disagreement regarding the connection between Abell 3367 and Abell 548. We use the available archival X-ray data together with kinematic data of counterpart galaxies to address this question and to determine the structure in this region. The region is particularly rich in X-ray structure elongated along a SW-NE axis consisting of numerous extended X-ray sources. In general, the structure consists of many galaxy groups and clusters which appear segregated in X-ray luminosity with the least luminous $\sim$ 30% toward the outer region of the clusters, possibly tracing a filament. We find evidence to suggest a supercluster of 3 clusters at redshifts: $\sim$ 0.04, 0.045, and 0.06. Some of the X-ray sources coincident with Abell 3367 have counterpart galaxy redshifts consistent with Abell 548 and others are significantly higher. This supports that Abell 548 and Abell 3667, form a supercluser and the higher redshift X-ray source is a background object. They are part of a larger structure consisting of a previously identified cluster at redshift 0.04, and two groups at redshift $\sim$ 0.06. In addition, there is a filamentary structure at z $\sim$ 0.103. The ubiquity of groups in the large scale structure suggests that they provide an environment where galaxies are in close proximity and evolution via interaction can proceed well before the galaxies make their way into the dense central region of a cluster.
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