Peer Revenue Impact factor: volatile

Papers

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

Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 2 October

Astrophysics of Galaxies

Improved Radiative Transfer Corrections in Helium Emission Lines

Oleg Kurichin and Alexandre Ivanchik

We present a new detailed model of the He I collisional-recombination spectrum based on the most up-to-date atomic data. The model accounts for radiative transfer effects and the influence of a non-zero optical depth in He I lines arising from transitions to the metastable 2^3S state. The model reveals substantial deviations in the emissivities of the lambda3889 and lambda7065 lines in the case of a non-zero optical depth, with previous models systematically underestimating and overestimating them by 5 to 20 percent, respectively. In the optically thin case, however, our results show good agreement with previous studies. Using the new model, we compute optically thin emissivities for a wide set of UV, optical, and IR He I recombination lines over a fine grid of electron densities and temperatures typical for H II regions and planetary nebulae (1 <= ne <= 10^4 cm^-3, 8000 <= Te <= 22000 K). In addition, we present new fitting formulae for radiative transfer corrections for several He I lines relevant to optical and near-infrared observations, covering 0 <= tau_3889 <= 10 within the same density and temperature ranges. The accuracy of the obtained approximations is <= 0.1 percent within the specified parameter range. These results can be readily implemented in modern codes for determining the primordial 4He abundance and are also applicable to a broader range of spectroscopic analyses of He I emission lines.
Read the full abstract

Solar and Stellar Astrophysics

Chemical transport by weakly nonlinear internal gravity waves in stars

Yifeng Mao and Daniel Lecoanet

While internal gravity waves (IGWs) are known to transport chemicals in the radiative zones of stars, substantial uncertainty remains regarding the magnitude and physical mechanisms of this transport. Most previous studies have relied on heuristic theories or numerical simulations that are difficult to extrapolate to stellar parameters. In this work, we present the first rigorous asymptotic calculation of (passive) chemical transport by IGWs, in the limit of small wave amplitude. The net vertical transport induced by a coherent packet of waves is found to be proportional to the horizontal mean of $(w^S+w^E)^2$, where $w^S$ and $w^E$ are the vertical Stokes and Eulerian mean velocities. The transport scales as the fourth power of wave amplitude and quadratically with time, and we verify these scalings with numerical simulations. In the weakly damped regime, the dominant transport coefficients scale as $\omega^{-2}\kappa^2$, where $\omega$ is the wave frequency and $\kappa$ is the radiative diffusivity. Because the transport can be positive or negative depending on the wave phases, the effective mixing induced by the superposition of coherent wave packets is expected to scale with the eighth power of wave amplitude. These results provide a theoretical foundation for making accurate predictions of IGW-induced chemical transport in stellar evolution models.
Read the full abstract

Solar and Stellar Astrophysics

A Large Sample of JWST/NIRSpec Brown Dwarfs: New Distant Discoveries

Zhijun Tu, Shu Wang, Xiaodian Chen et al. (+1 more)

Brown dwarfs are essential probes of stellar and planetary formation, yet their low luminosities pose challenges for detection at large Galactic distances. The James Webb Space Telescope (JWST), with its unprecedented near-infrared sensitivity, enables the discovery and characterization of distant substellar objects, including those in the Milky Way's thick disk and halo. We conducted a systematic search using over 40,000 publicly available JWST/NIRSpec PRISM/CLEAR spectra and identified 68 brown dwarfs through spectral template matching and visual inspection. Among them, 12 are newly identified candidates, including 8 T dwarfs and 4 M/L dwarfs, most at distances exceeding 1 kpc. Remarkably, two sources – JWST J001418.22-302223.2 and JWST J033240.07-274907.8 – are found at distances greater than 5 kpc, making them the most distant brown dwarfs within the Milky Way. Spectral fits were performed using a nested sampling Monte Carlo algorithm with three model grids: Sonora Elf Owl, LOWZ, and SAND. The analysis reveals that cloud-free models are unable to reproduce L/T transition spectra, whereas the SAND model provides a more accurate representation of cloud effects in metal-poor environments. With the newly identified distant brown dwarfs, we also investigated the vertical metallicity gradient of brown dwarfs. Overall, the metallicities do not show an evident trend with Galactic height $|Z|$, due to the limited sample size and the uncertainties in metallicity measurements.
Read the full abstract

All authors Zhijun Tu, Shu Wang, Xiaodian Chen, Jifeng Liu

Instrumentation and Methods for Astrophysics

Design and Scientific Prospects of the POLAR-2 Mission

Merlin Kole, Nicolas de Angelis, Jiang He et al. (+4 more)

The POLAR-2 mission consists of 3 instruments designed with the combined aim of producing a deeper understanding of Gamma-Ray Bursts. To achieve this, POLAR-2 relies on polarisation measurements and, for the first time will provide these using 2 separate polarimeter detectors. The first of these is a payload optimised to perform Compton polarimetry measurements in the 40-1000 keV energy range using a combination of plastic scintillators and SiPMs. The development of this payload, the design of which is based on lessons learned from the POLAR mission, included optimization of plastic scintillator design. In addition, its development included detailed characterization, space qualification and radiation damage and mitigation strategies for the large number of silicon photo-multipliers included in the design. We will present these along with an overview of the readout electronics. These electronics were developed with flexibility in mind, as well as low cost and low power consumption. As such, its design is of interest beyond this polarimeter and is also used on the spectrometer instrument of POLAR-2 where it is used to read out an array of GAGG:Ce scintillators. This readout, in combination with a coded mask, allows this secondary instrument to provide detailed spectral and localization measurements. The final instrument used in the mission aims to use gas-based detectors to perform polarization measurements in the keV energy region. The novelty of this design is that it will be optimized to use these for wide field of view observations. The combination of the three instruments will allow to perform detailed spectral, localization and polarization measurements of these transient phenomena together for the first time. Here we provide an overview of the technologies employed in the mission along with detailed predictions on its capabilities after its launch currently foreseen in 2027.
Read the full abstract

All authors Merlin Kole, Nicolas de Angelis, Jiang He, Hongbang Liu, Jianchao Sun, Fei Xie, Jimmy Zaid

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

The trichotomy of primordial black holes initial conditions

Cristiano Germani and Laia Montellà

We show that the threshold to form a black hole, in an asymptotically flat and radiation-dominated Friedman-Robertson-Walker (FRW) Universe, is not solely (mainly) determined by the behaviour of the compaction function at its extrema, as earlier thought, but also by the Ricci scalar of the spatial geometry at smaller (but super-horizon) scales, which we call “the core”. We introduce three classes of initial conditions characterised by an open (O), closed (C), or flat (F) FRW core surrounded by a shell with higher three-dimensional curvature. In the C case, the core helps the collapse so that the black hole formation threshold is the lowest among all cases. Type-II black holes might only be generated by Type-O or F (each of those with different thresholds, with O being the highest) or by a Type-C with a negligible Ricci scalar at the centre, which we call an effective F core. Finally, we argue that an F core is typically more probable for a sharp power spectrum, however, it is also more likely related to non-spherical initial conditions. On the other hand, a very broad power spectrum, which might be related to the observed NanoGrav signal, would favour the formation of Type-I black holes with a mass spectrum peaked at the Infra-Red scale.
Read the full abstract

Earth and Planetary Astrophysics

Mercury's Crustal Magnetization Indicates a Stronger Ancient Dynamo

Isaac S. Narrett, Benjamin P. Weiss, Sarah C. Steele et al. (+1 more)

Mercury is the only terrestrial planet in the solar system other than Earth with an active dynamo magnetic field (~200 nT at the equatorial surface). Furthermore, Mercury's ~3.9-3.7-billion-year-old (Ga) crust is strongly magnetized (~10 nT at ~30-km altitude), indicating the presence of a past dynamo. However, the strength of the past dynamo field and the mechanism that generated it are unknown. To address this, we performed three-dimensional magnetohydrodynamic simulations of the ancient solar wind interaction with the planetary field coupled with crustal thermal evolution and magnetization models. We show that the crustal magnetization was likely produced by a dipole field with equatorial surface strength of at least ~2,000 nT and possibly as high as ~30,000 nT for a dynamo with a reversal frequency greater than once per million years. Such strong fields likely exclude both the solar wind feedback and thermoelectric dynamo mechanisms at 3.7 Ga ago. Instead, our results are compatible with the past dynamo being generated by a nearly fully convective core.
Read the full abstract

All authors Isaac S. Narrett, Benjamin P. Weiss, Sarah C. Steele, John B. Biersteker

Astrophysics of Galaxies

RAD@home discovery of extragalactic radio rings and odd radio circles: clues to their origins

Ananda Hota, Pratik Dabhade, Prasun Machado et al. (+3 more)

We present three rare and striking extragalactic radio sources discovered through visual inspection of low-frequency continuum maps from LoTSS DR2 and TGSS by the RAD@home citizen-science collaboratory. The first, RAD J131346.9+500320, is the first clear Odd Radio Circle (ORC) identified in LoTSS. At photometric $z \sim$ 0.94, it hosts a pair of intersecting rings of ~300 kpc diameter, embedded in diffuse emission extending over ~800 kpc, making it both the most distant and most powerful ORC reported to date. Its steep spectrum $\alpha_{54}^{144}=1.22\pm0.15$) points to a relic synchrotron origin. The second object, RAD J122622.6+640622, is a ~865 kpc giant radio galaxy whose southern jet is abruptly deflected, inflating a ~100 kpc limb-brightened ring, while the northern jet terminates in a compact hotspot-like feature. The third, RAD J142004.0+621715 (~440 kpc), shows a comparable ring at the end of its northern filamentary jet, along with a secondary filament parallel to its southern jet. All three systems lie in $\sim10^{14}M_\odot$ clusters or group-scale haloes, suggesting that environmental density gradients and possible jet-galaxy interactions play a central role in shaping these ring morphologies. These discoveries expand the zoo of extragalactic radio morphologies, highlight the diversity of pathways that can generate ring-like synchrotron structures, and demonstrate the continuing importance of human pattern recognition in identifying rare sources that escape current automated pipelines.
Read the full abstract

All authors Ananda Hota, Pratik Dabhade, Prasun Machado, Joydeep Das, Aarti Muley, Arundhati Purohit

Earth and Planetary Astrophysics

A decade of transit photometry for K2-19: Revised system architecture

J.M. Almenara, R. Mardling, A. Leleu et al. (+21 more)

The star K2-19 hosts a pair of Neptunian planets deep inside the 3:2 resonance. They induce strong transit-timing variations with two incommensurate frequencies. Previous photodynamical modeling of 3.3 years of transit and radial velocity data produced mass estimates of 32.4 +/- 1.7 M_E and 10.8 +/- 0.6 M_E for planets b and c, respectively, and corresponding eccentricity estimates of 0.20 +/- 0.03 and 0.21 +/- 0.03. These high eccentricities raise questions about the formation origin of the system, and this motivated us to extend the observing baseline in an attempt to better constrain their values. We present a photodynamical analysis of 10 years of transit data that confirms the previous mass estimates (30.8 +/- 1.3 M_E and 11.1 +/- 0.4 M_E), but reduces the median eccentricities to 0.04 +/- 0.02 and 0.07 +/- 0.02 for b and c, respectively. These values are more consistent with standard formation models, but still involve nonzero free eccentricity. The previously reported high eccentricities appear to be due to a single transit for which measurements taken at twilight mimicked ingress. This resulted in a 12-minute error in the midtransit time. The data that covered 1.3 and 5 so-called super and resonant periods were used to match a Fourier analysis of the transit-timing variation signal with simple analytic expressions for the frequencies and amplitudes to obtain planet mass estimates within 2% of the median photodynamical values, regardless of the eccentricities. Theoretical details of the analysis are presented in a companion paper. Additionally, we identified a possible planet candidate situated exterior to the b-c pair. Finally, in contrast to a previous study, our internal structure modeling of K2-19 b yields a metal mass fraction that is consistent with core accretion.
Read the full abstract

All authors J.M. Almenara, R. Mardling, A. Leleu, R.F. Díaz, X. Bonfils, Ing-Guey Jiang, Li-Chin Yeh, Ming Yang, Keivan G. Stassun, Napaporn A-thano, Billy Edwards, F. Bouchy, V. Bourrier, A. Deline, D. Ehrenreich, E. Fontanet, T. Forveille, J.M. Jenkins, L.K.W. Kwok, M. Lendl, A. Psaridi, S. Udry, J. Venturini, J. Winn

Earth and Planetary Astrophysics

Impact Plasma Amplification of the Ancient Mercury Magnetic Field

Isaac S. Narrett, Rona Oran, Yuxi Chen et al. (+4 more)

Spacecraft measurements of Mercury indicate it has a core dynamo with a surface field of 200-800 nT. These data also indicate that the crust contains remanent magnetization likely produced by an ancient magnetic field. The inferred magnetization intensity is consistent with a wide range of paleofield strengths (0.2-50 uT), possibly indicating that Mercury once had a dynamo field much stronger than today. Recent modeling of ancient lunar impacts has demonstrated that plasma generated during basin-formation can transiently amplify a planetary dynamo field near the surface. Simultaneous impact-induced pressure waves can then record these fields in the form of crustal shock remanent magnetization (SRM). Here, we present impact hydrocode and magnetohydrodynamic simulations of a Caloris-size basin (~1,550 km diameter) formation event. Our results demonstrate that the ancient magnetospheric field (~0.5-0.9 uT) created by the interaction of the ancient interplanetary magnetic field (IMF) and Mercury's dynamo field can be amplified by the plasma up to ~13 uT and, via impact pressure waves, be recorded as SRM in the basin antipode. Such magnetization could produce ~5 nT crustal fields at 20-km altitude antipodal to Caloris detectable by future spacecraft like BepiColombo. Furthermore, impacts in the southern hemisphere that formed ~1,000 km diameter basins (e.g., Andal-Coleridge, Matisse-Repin, Eitkou-Milton, and Sadi-Scopus) could impart crustal magnetization in the northern hemisphere, contributing to the overall remanent field measured by MESSENGER. Overall, the impact plasma amplification process can contribute to crustal magnetization on airless bodies and should be considered when reconstructing dynamo history from crustal anomaly measurements.
Read the full abstract

All authors Isaac S. Narrett, Rona Oran, Yuxi Chen, Katarina Miljković, Gábor Tóth, Catherine L. Johnson, Benjamin P. Weiss

Cosmology and Nongalactic Astrophysics

BAO miscalibration cannot rescue late-time solutions to the Hubble tension

Davide Pedrotti, Luis A. Escamilla, Valerio Marra et al. (+2 more)

Baryon Acoustic Oscillation (BAO) measurements play a key role in ruling out post-recombination solutions to the Hubble tension. However, because the data compression leading to these measurements assumes a fiducial $\Lambda$CDM cosmology, their reliability in testing late-time modifications to $\Lambda$CDM has at times been called into question. We play devil's advocate and posit that fiducial cosmology assumptions do indeed affect BAO measurements in such a way that low-redshift acoustic angular scales (proportional to the Hubble constant $H_0$) are biased low, and test whether such a rescaling can rescue post-recombination solutions. The answer is no. Firstly, strong constraints on the shape of the $z \lesssim 2$ expansion history from unanchored Type Ia Supernovae (SNeIa) prevent large deviations from $\Lambda$CDM. In addition, unless $\Omega_m$ is significantly lower than $0.3$, the rescaled BAO measurements would be in strong tension with geometrical information from the Cosmic Microwave Background. We demonstrate this explicitly on several dark energy (DE) models ($w$CDM, CPL DE, phenomenologically emergent DE, holographic DE, $\Lambda_s$CDM, and the negative cosmological constant model), finding that none can address the Hubble tension once unanchored SNeIa are included. We argue that the $\Lambda_s$CDM sign-switching cosmological constant model possesses interesting features which make it the least unpromising one among those tested. Our results demonstrate that possible fiducial cosmology-induced BAO biases cannot be invoked as loopholes to the Hubble tension "no-go theorem", and highlight the extremely important but so far underappreciated role of unanchored SNeIa in ruling out post-recombination solutions.
Read the full abstract

All authors Davide Pedrotti, Luis A. Escamilla, Valerio Marra, Leandros Perivolaropoulos, Sunny Vagnozzi

Astrophysics of Galaxies

The Disk Plus (Failed) Wind System of 3C 47: A Story of Accretion Disks and Binary Black Holes

P. Marziani, S. Terefe Mengistue, A. del Olmo et al. (+9 more)

[Abridged] Optically thick, geometrically thin accretion disks around supermassive black holes are thought to contribute to broad-line emission in type-1 active galactic nuclei (AGN). However, observed emission line profiles most often deviate from those expected from a rotating disk. This report examines the role of accretion disks in broad-line emission of Population B AGN characterized by relatively low accretion rates in which broad lines show large redward asymmetry both in H$\beta$ and Mg II$\lambda$ 2800. An unbiased comparison matching black hole mass and Eddington ratio suggests that the most powerful radio-loud quasars show the highest red-ward asymmetries in H$\beta$. These shifts can be accounted for by gravitational and transverse redshift effects, especially for black hole masses larger than $\approx$10$^{8.7}$ M$_\odot$. The analysis of the extremely jetted quasar 3C 47 adds another piece to the puzzle: not only are the low ionization profiles of 3C 47 well-described by a relativistic Keplerian accretion disk model, with line emission in the range 100 - 1,000 gravitational radii, but also the high-ionization line profiles can be understood as a combination of disk plus a failed wind contribution that is in turn hiding the disk emission. Constraints on radio properties and line profile variability suggest that 3C 47 might involve the presence of a second black hole with secondary-to-primary mass ratio $\sim$ 0.5. We conjecture that the double peakers - type-1 AGN with Balmer line profiles consistent with accretion disk emission - might have their emission truncated by the sweeping effect of a second black hole. In non-starving systems, the disk signal is plausibly masked by additional line emission, rendering the disk contribution harder to detect.
Read the full abstract

All authors P. Marziani, S. Terefe Mengistue, A. del Olmo, M. Povič, J. Perea, S. Komossa, E. Bon, N. Bon, L. Č. Popovič, A. Deconto-Machado, I. Marquez, M. A. Martínez Carballo

Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det

Dark characterization of Ti/Al LEKIDs for the search of axions in the W-band

Victor Rollano, Alejandro Pascual Laguna, David Rodriguez et al. (+5 more)

We report the electrical (dark) characterization of lumped-element kinetic inductance detectors (LEKIDs) fabricated from a Titanium/Aluminum bilayer and designed for broadband absorption in the W-band (75-110 GHz). These detectors are prototypes for future QCD axion search experiments within the Canfranc Axion Detection Experiment (CADEx), which demand sub 1e-19 W/Hz^0.5 sensitivities under low optical backgrounds. We combine a Mattis-Bardeen analysis to the temperature dependence of the detector parameters with noise spectroscopy to determine the electrical noise equivalent power (NEP). The minimum measured value for the electrical NEP is 3e-19 W/Hz0.5. Across the measured temperature range, we find that quasiparticle lifetime deviates from the expected BCS recombination law. Our analysis suggests that non-equilibrium relaxation is governed by spatial inhomogeneities in the superconducting gap and phonon diffusion effects. This work sets the road-map to achieve suitable and ultra-sensitive detectors in the W-band for dark matter axion search experiments.
Read the full abstract

All authors Victor Rollano, Alejandro Pascual Laguna, David Rodriguez, Martino Calvo, Maria Teresa Magaz, Daniel Granados, Alessandro Monfardini, Alicia Gomez

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

Resonant production of sterile neutrino dark matter with a refined numerical scheme

Kentaro Kasai, Masahiro Kawasaki and Kai Murai

The existence of a large primordial neutrino asymmetry is an intriguing possibility, both observationally and theoretically. Such an asymmetry can lead to the resonant production of $\mathrm{keV}$-scale sterile neutrinos, which are a fascinating candidate for dark matter. In this paper, we comprehensively revisit the resonant production processes with a refined numerical analysis, adopting a dynamical discretization of momentum modes to take care of the sharpness of the resonance. We find parameter regions consistent with X-ray and Lyman-$\alpha$ constraints for lepton-to-entropy ratio $\gtrsim \mathcal{O}(10^{-3})$ and $m_{\nu_s}\gtrsim 20\,$keV. We also explore the Affleck-Dine mechanism as a possible origin for such asymmetries. While previous studies considered resonant production after lepton number generation, we numerically investigate cases where a fraction of sterile neutrinos is produced during lepton number injection. In this regime, some parameter sets can shorten the free-streaming length and reduce the required mixing angle to match the observed dark matter abundance, thereby mitigating the observational constraints.
Read the full abstract

Astrophysics of Galaxies

Impact of AGB stars on the chemical evolution of neutron-capture elements

Gabriele Cescutti and Francesca Matteucci

In this paper we discuss the impact of the s-process nucleosynthesis in Asymptotic Giant Branch stars on the enrichment of heavy elements. We review the main steps made on this subject in the last 40 years and discuss the importance of modelling the evolution of the abundances of such elements in our Milky Way. From the comparison between model results and observations, we can impose strong constraints on stellar nucleosynthesis as well as on the evolution of the Milky Way.
Read the full abstract

Instrumentation and Methods for Astrophysics

Cross-Polarization Reduction in Kinetic Inductance Detectors Based on Quasi-Lumped Resonators

Victor Rollano, Martino Calvo, Alejandro Pascual Laguna et al. (+7 more)

Kinetic Inductance Detectors (KIDs) have emerged as a leading technology for millimeter- and submillimeter-wave astronomy due to their high sensitivity, natural multiplexing capabilities and scalable fabrication. In polarization-sensitive applications-such as Cosmic Microwave Background (CMB) studies-cross-polarization, or unintended response to the orthogonal polarization, poses a significant limitation to measurement fidelity. This work investigates the origin of cross-polarization in meandered Lumped Element KIDs (LEKIDs), with particular emphasis on the role of parasitic currents in the interdigitated capacitor. A comparative study between conventional LEKIDs and a quasi-lumped resonator design is presented, demonstrating that removing the capacitive element may improve cross-polarization discrimination, confirming the capacitor's contribution to polarization leakage.
Read the full abstract

All authors Victor Rollano, Martino Calvo, Alejandro Pascual Laguna, David Rodriguez, Maria Teresa Magaz, Beatriz Aja, Luisa de la Fuente, Daniel Granados, Alessandro Monfardini, Alicia Gomez

High Energy Astrophysical Phenomena

Constraining the Neutron-Star Equation of State via Short Gamma-Ray Burst X-ray Afterglows

R. Moradi, Y. Wang, F. Rastegarnia et al. (+4 more)

Recent observations from NICER in X-rays and LIGO/Virgo in gravitational waves have provided critical constraints on the mass, radius, and tidal deformability of neutron stars, imposing stringent limits on the equation of state (EOS) and the behavior of ultra-dense matter. However, several key parameters influencing the EOS, such as the maximum mass of neutron stars, spin-down rates, and the potential role of exotic matter in their cores, remain subject of ongoing debate. Here we present a new approach to constraining the EOS by analyzing the X-ray afterglows of some short gamma-ray bursts, focusing on "the internal plateau" phase and its abrupt decay, which reflect the spin-down and possible collapse of a supra-massive neutron star into a black hole. By linking critical neutron star masses with black hole formation criteria and the observational data from Swift's BAT and XRT instruments with compact object models, we explore three representative EOSs that range from "soft" to "stiff". Our result supports a maximum mass for neutron stars of approximately 2.39 solar masses at the threshold of black hole formation. This conclusion holds under assumptions of magnetar-powered X-ray plateaus, constant radiative efficiency, isotropic emission, and full Kerr black hole energy extraction; deviations could influence the inferred results. Our results demonstrate the critical role of neutron star/black hole physics in probing dense nuclear matter and provide a novel framework for exploring extreme astrophysical environments.
Read the full abstract

All authors R. Moradi, Y. Wang, F. Rastegarnia, E. S. Yorgancioglu, Shu-Xu Yi, B. Eslam Panah, S. N. Zhang

Solar and Stellar Astrophysics

Low- and high-velocity `water fountains': different evolutionary stages

Roldán A. Cala, Luis F. Miranda, José F. Gómez et al. (+1 more)

`Water fountains' (WFs) are optically obscured evolved stars, most of them thought to be in the post-asymptotic giant branch (post-AGB) phase, characterized by H$_{2}$O maser emission tracing molecular jets. Interestingly, four WFs (IRAS 15445$-$5449, IRAS 18019$-$2216, IRAS 18443$-$0231, and IRAS 18464$-$0140) and one WF candidate (IRAS 18480+0008) are potential planetary nebulae (PNe) because they exhibit radio continuum emission, suggesting the presence of a photoionized region characteristic of PNe. To classify these objects, we obtained K-band (2.0-2.3 $\mu$m) spectra of these WFs, including the only WF PN known (IRAS 15103$-$5754) for comparison. Our spectra reveal two group of sources: (i) `low-velocity' WFs with H$_2$O maser velocity spread of $\lesssim$50 km s$^{-1}$ (IRAS 18019$-$2216, IRAS 18464$-$0140, and IRAS 18480+0008) showing the CO band at 2.29 $\mu$m in absorption, typical of cool giant stars, and no emission lines; and (ii) `high-velocity' WFs, velocity spread of $\gtrsim$50 km s$^{-1}$ (IRAS 15103$-$5754, IRAS 15445$-$5449, and IRAS 18443$-$0231), exhibiting emission lines of Br$\gamma$, He I, and H$_2$, consistent with hotter central stars and/or shock-excited emission. The emission line ratios of these lines in IRAS 18443$-$0231 indicates that it may be a nascent PN. The spectrum of IRAS 15445$-$5449 also shows a CO band and Na I doublet in emission, suggesting the presence of a compact circumstellar disk and/or active mass loss. These results favor the previously suggested notion that the difference between low- and high-velocity WFs is not simply a projection effect but reflects intrinsically different evolutionary stages. Moreover, the results are also consistent with the idea of an increase in the jet ejection velocity as the post-AGB evolution proceeds.
Read the full abstract

All authors Roldán A. Cala, Luis F. Miranda, José F. Gómez, Keiichi Ohnaka

Solar and Stellar Astrophysics

PRESOL: a web-based computational setting for feature-based flare forecasting

Chiara Curletto, Paolo Massa, Valeria Tagliafico et al. (+4 more)

Solar flares are the most explosive phenomena in the solar system and the main trigger of the events' chain that starts from Coronal Mass Ejections and leads to geomagnetic storms with possible impacts on the infrastructures at Earth. Data-driven solar flare forecasting relies on either deep learning approaches, which are operationally promising but with a low explainability degree, or machine learning algorithms, which can provide information on the physical descriptors that mostly impact the prediction. This paper describes a web-based technological platform for the execution of a computational pipeline of feature-based machine learning methods that provide predictions of the flare occurrence, feature ranking information, and assessment of the prediction performances.
Read the full abstract

All authors Chiara Curletto, Paolo Massa, Valeria Tagliafico, Cristina Campi, Federico Benvenuto, Michele Piana, Andrea Tacchino

Instrumentation and Methods for Astrophysics

cuHPX: GPU-Accelerated Differentiable Spherical Harmonic Transforms on HEALPix Grids

Xiaopo Cheng, Akshay Subramaniam, Shixun Wu et al. (+1 more)

HEALPix (Hierarchical Equal Area isoLatitude Pixelization) is a widely adopted spherical grid system in astrophysics, cosmology, and Earth sciences. Its equal-area, iso-latitude structure makes it particularly well-suited for large-scale data analysis on the sphere. However, implementing high-performance spherical harmonic transforms (SHTs) on HEALPix grids remains challenging due to irregular pixel geometry, latitude-dependent alignments, and the demands for high-resolution transforms at scale. In this work, we present cuHPX, an optimized CUDA library that provides functionality for spherical harmonic analysis and related utilities on HEALPix grids. Beyond delivering substantial performance improvements, cuHPX ensures high numerical accuracy, analytic gradients for integration with deep learning frameworks, out-of-core memory-efficient optimization, and flexible regridding between HEALPix, equiangular, and other common spherical grid formats. Through evaluation, we show that cuHPX achieves rapid spectral convergence and delivers over 20 times speedup compared to existing libraries, while maintaining numerical consistency. By combining accuracy, scalability, and differentiability, cuHPX enables a broad range of applications in climate science, astrophysics, and machine learning, effectively bridging optimized GPU kernels with scientific workflows.
Read the full abstract

All authors Xiaopo Cheng, Akshay Subramaniam, Shixun Wu, Noah Brenowitz

High Energy Astrophysical Phenomena

Identifying tidal disruption events among radio transient galaxies

M. Kunert-Bajraszewska, D. Kozieł-Wierzbowska, D. Stern et al. (+4 more)

We present the optical and infrared properties of a sample of 24 radio transient sources discovered in the Very Large Array Sky Survey (VLASS). Previous studies of their radio emission showed that these sources resemble young gigahertz-peaked spectrum (GPS) radio sources, but are less powerful and characterized by low-power jets. The bursts of radio activity in most cases are likely due to intrinsic changes in the accretion processes. However, for a few sources in this sample, we cannot rule out the possibility that their radio variability results from a tidal disruption event (TDE). In this work, we extend our analysis to the optical and infrared regimes, confirming that our sample of radio transients is not homogeneous in terms of their optical and infrared properties either. The host galaxies of most of these sources are massive ellipticals with emission dominated by active galactic nuclei (AGN). They host supermassive black holes (SMBHs) with masses typical of radio-loud AGNs ($\rm >10^7\,M_{\odot}$), but exhibit very low accretion activity. In contrast, the sources for which a TDE origin is suspected are either pure star-forming galaxies or show significant ongoing star formation, similar to radio-selected optically-detected TDEs. Additionally, two of them exhibit infrared flares characteristic of TDEs, while the remaining sources do not display significant variability outside the radio regime. Moreover, the evolution of their radio brightness in the W3/radio diagnostic diagram, which we employ in our analysis, also sets our TDE candidates apart from the rest of the sample and resembles the radio variability seen in optically discovered TDEs with radio emission. Finally, based on our findings, we hypothesize that the mid-IR/radio relation can serve as a tool to distinguish between radio transients caused by TDEs and those originating from intrinsic AGN variability.
Read the full abstract

All authors M. Kunert-Bajraszewska, D. Kozieł-Wierzbowska, D. Stern, A. Krauze, N. Zafar, T. Connor, M. J. Graham

Solar and Stellar Astrophysics

Discovery of an Accretion Burst in a Free-Floating Planetary-Mass Object

V. Almendros-Abad, A. Scholz, B. Damian et al. (+7 more)

We report the discovery of a long-lasting burst of disk accretion in Cha J11070768-7626326 (Cha 1107-7626), a young, isolated, 5-10 M$_{\mathrm{Jupiter}}$ object. In spectra taken with XSHOOTER at ESO's Very Large Telescope as well as NIRSPEC and MIRI on the James Webb Space Telescope, the object transitions from quiescence in April-May 2025 to a strongly enhanced accretion phase in June-August 2025. The line flux changes correspond to a 6-8-fold increase in the mass accretion rate, reaching $10^{-7}$ M$_{\mathrm{Jupiter}}$yr$^{-1}$, the highest measured in a planetary-mass object. During the burst, the H$\alpha$ line develops a double-peaked profile with red-shifted absorption, as observed in stars and brown dwarfs undergoing magnetospheric accretion. The optical continuum increases by a factor of 3-6; the object is $\sim$1.5-2 mag brighter in the R-band during the burst. Mid-infrared continuum fluxes rise by 10-20%, with clear changes in the hydrocarbon emission lines from the disk. We detect water vapour emission at 6.5-7 $\mu m$, which were absent in quiescence. By the end of our observing campaign, the burst was still ongoing, implying a duration of at least two months. A 2016 spectrum also shows high accretion levels, suggesting that this object may undergo recurring bursts. The observed event is inconsistent with typical variability in accreting young stars and instead matches the duration, amplitude and line spectrum of an EXor-type burst, making Cha1107-7626 the first substellar object with evidence of a potentially recurring EXor burst.
Read the full abstract

All authors V. Almendros-Abad, A. Scholz, B. Damian, R. Jayawardhana, A. Bayo, L. Flagg, K. Muzic, A. Natta, P. Pinilla, L. Testi

High Energy Astrophysical Phenomena

Instabilities at recollimation shocks in MHD jets

Stella Boula, Fabrizio Tavecchio, Gianluigi Bodo et al. (+4 more)

AGN jet structure and stability remain uncertain; recollimation shocks are linked to morphology and variability, but the role of downstream instabilities is still unclear. We aim to investigate how jet magnetization and other physical parameters influence the development of instabilities beyond the first recollimation shock. In particular, we focus on identifying the conditions under which the centrifugal instability (CFI) is effective. We perform high-resolution 2D and 3D simulations using the relativistic magnetohydrodynamics code PLUTO. The jets are initialized with a conical geometry and propagate into an ambient medium, and we follow by axisymmetric simulations how they evolve towards a steady-state. In 2D we explore a range of magnetizations (from 0 to 1), pressure contrasts, and inertia ratios to characterize the formation and evolution of recollimation shocks. The results are further evaluated using linear stability analysis to assess the growth and suppression of CFI. Finally, we perform 3D simulations of unstable and stable jets. We discuss how the different parameters of the axisymmetric steady solutions influence the location and strength of recollimation. We find that, even in moderately magnetized jets, $\sigma$=0.1, the CFI can still develop under suitable local conditions and disrupt the jet structure. This instability is governed by the jet radius, curvature, Lorentz factor, and magnetization, and is not always predictable from injection conditions. While magnetization can delay or locally suppress instability growth, it does not guarantee long-term jet stability. Our 3D results highlight the limitations of 2D models in capturing non-axisymmetric and nonlinear effects, and underline the complex interplay between magnetic confinement and destabilizing mechanisms. These findings have implications for interpreting variability, and polarization structure in AGN jets.
Read the full abstract

All authors Stella Boula, Fabrizio Tavecchio, Gianluigi Bodo, Nektarios Vlahakis, Paolo Coppi, Agnese Costa, Alberto Sciaccaluga

High Energy Astrophysical Phenomena

Exploring GRB Afterglows in the TeV Era: New Diagnostics of Particle Acceleration

L. Foffano and M. Tavani

The TeV gamma-ray band is essential for probing the most extreme particle acceleration processes in the Universe. The recent detections of gamma-ray bursts (GRBs) at these energies offer an incredible opportunity to investigate the origins of such transient events in an unprecedented way. In this presentation, we analyze the afterglows of these GRBs by modeling their synchrotron and inverse Compton emission within an optimized relativistic fireball framework. By comparing observational data with theoretical predictions, we constrain key model parameters and track their temporal evolution. The comparison of different TeV-detected GRBs reveals an intriguing variety among them, potentially reflecting differences in the particle acceleration processes that have to be very fast and able to accelerate to large energies. We discuss how late-time afterglow observations of X-ray and GeV-TeV emissions are crucial for providing diagnostics into the physics of GRBs. At this scope, we also present the most updated results of the AGILE telescope, which support our interpretation. Finally, we highlight theoretical predictions for future TeV observations and their implications for understanding these extreme cosmic explosions.
Read the full abstract

Instrumentation and Methods for Astrophysics · Cross-listed from hep-ex

Reducing Simulation Dependence in Neutrino Telescopes with Masked Point Transformers

Felix J. Yu, Nicholas Kamp and Carlos A. Argüelles

Machine learning techniques in neutrino physics have traditionally relied on simulated data, which provides access to ground-truth labels. However, the accuracy of these simulations and the discrepancies between simulated and real data remain significant concerns, particularly for large-scale neutrino telescopes that operate in complex natural media. In recent years, self-supervised learning has emerged as a powerful paradigm for reducing dependence on labeled datasets. Here, we present the first self-supervised training pipeline for neutrino telescopes, leveraging point cloud transformers and masked autoencoders. By shifting the majority of training to real data, this approach minimizes reliance on simulations, thereby mitigating associated systematic uncertainties. This represents a fundamental departure from previous machine learning applications in neutrino telescopes, paving the way for substantial improvements in event reconstruction and classification.
Read the full abstract

Earth and Planetary Astrophysics

High five from ASTEP: Three validated planets and two eclipsing binaries in a diverse set of long-period candidates

Erika Rea, Maximilian N. Günther, George Dransfield et al. (+44 more)

We present the analysis of five long-period TESS Objects of Interest (TOIs), all orbiting Sun-like stars, with orbital periods exceeding one month. Initially identified by the Transiting Exoplanet Survey Satellite (TESS), we extensively monitored these targets with the Antarctic Search for Transiting Exoplanets (ASTEP), supported by other facilities in the TESS Follow-up Observing Program (TFOP) network. These targets occupy a relatively underexplored region of the period-radius parameter space, offering valuable primordial probes for planetary formation and migration as warm planets better maintain their evolutionary fingerprints. To characterise these systems, we leveraged high-resolution speckle imaging to search for nearby stellar companions, and refine stellar parameters using both reconnaissance spectroscopy and spectral energy distribution (SED) fitting. We combined TESS photometry with high-precision ground-based observations from ASTEP, and when available, included additional photometry and radial velocity data. We applied statistical validation to assess the planetary nature of each candidate and used Allesfitter to jointly model the photometric and spectroscopic datasets. We validate the planetary nature of three TOIs, including the two warm Saturns TOI-4507b (8.2 Earth radii, 104d) and TOI-3457b (10.0 Earth radii, 32.6d), as well as the warm sub-Neptune TOI-707b (2.4 Earth radii, 52.8d). The remaining two candidates are most consistent with eclipsing binaries, namely TOI-2404 and TOI-4404. These results help populate the sparse regime of warm planets, which serve as key tracers of planetary evolution, and demonstrate ASTEP's effectiveness as a ground-based follow-up instrument for long-period systems.
Read the full abstract

All authors Erika Rea, Maximilian N. Günther, George Dransfield, Tristan Guillot, Amaury H.M.J. Triaud, Keivan G. Stassun, Juan I. Espinoza-Retamal, Rafael Brahm, Solène Ulmer-Moll, Matteo Beltrame, Vincent Deloupy, Mathilde Timmermans, Lyu Abe, Karim Agabi, Philippe Bendjoya, Djamel Mekarnia, Francois-Xavier Schmider, Olga Suarez, Ana M. Heras, Theresa Lüftinger, Bruno Merín, François Bouchy, Thomas Henning, Andrés Jordán, Monika Lendl, Marcelo Tala-Pinto, Trifon Trifonov, Khalid Barkaoui, Luke G. Bouma, Gavin Boyle, César Briceño, Amadeo Castro-González, Alastair Claringbold, Karen A. Collins, Keith Horne, Steve B. Howell, Andrew W. Mann, Felipe Murgas, Enric Palle, Samuel Quinn, Joseph E. Rodriguez, Richard P. Schwarz, T.G. Tan, George Zhou, Carl Ziegler, Sara Seager, Joshua N. Winn

High Energy Astrophysical Phenomena

Dedicated-frequency analysis of gravitational-wave bursts from core-collapse supernovae with minimal assumptions

Yi Shuen C. Lee, Marek J Szczepańczyk, Tanmaya Mishra et al. (+2 more)

Gravitational-wave (GW) emissions from core-collapse supernovae (CCSNe) provide insights into the internal processes leading up to their explosions. Theory predicts that CCSN explosions are driven by hydrodynamical instabilities like the standing accretion shock instability (SASI) or neutrino-driven convection, and simulations show that these mechanisms emit GWs at low frequencies ($\lesssim 0.25 \,{\rm kHz}$). Thus the detection of low-frequency GWs, or lack thereof, is useful for constraining explosion mechanisms in CCSNe. This paper introduces the dedicated-frequency framework, which is designed to follow-up GW burst detections using bandpass analyses. The primary aim is to study whether low-frequency (LF) follow-up analyses, limited to $\leq 256 \,{\rm Hz}$, constrain CCSN explosion models in practical observing scenarios. The analysis dataset comprises waveforms from five CCSN models with different strengths of low-frequency GW emissions induced by SASI and/or neutrino-driven convection, injected into the Advanced LIGO data from the Third Observing Run (O3). Eligible candidates for the LF follow-up must satisfy a benchmark detection significance and are identified using the coherent WaveBurst (cWB) algorithm. The LF follow-up analyses are performed using the BayesWave algorithm. Both cWB and BayesWave make minimal assumptions about the signal's morphology. The results suggest that the successful detection of a CCSN in the LF follow-up analysis constrains its explosion mechanism. The dedicated-frequency framework also has other applications. As a demonstration, the loudest trigger from the SN 2019fcn supernova search is followed-up using a high-frequency (HF) analysis, limited to $\geq 256 \,{\rm Hz}$. The trigger has negligible power below $256 \, {\rm Hz}$, and the HF analysis successfully enhances its detection significance.
Read the full abstract

All authors Yi Shuen C. Lee, Marek J Szczepańczyk, Tanmaya Mishra, Margaret Millhouse, Andrew Melatos

Cosmology and Nongalactic Astrophysics

Realistic Oscillon Interactions

Angela Xue, Kyle Chen, Baylee Verzyde et al. (+2 more)

Oscillons are long-lived nonlinear pseudo-solitonic configurations of scalar fields and many plausible inflationary scenarios predict an oscillon-dominated phase in the early universe. Many possible aspects of this phase remain unexplored, particularly oscillon-oscillon interactions and interactions between oscillons and their environment. However the primary long range forces between oscillons are gravitational and thus slow-acting relative to the intrinsic timescales of the oscillons themselves. Given that simulations with local gravity are computationally expensive we explore these effects by extracting individual specimens from simulations and then engineering interactions. We find that oscillons experience friction when moving in an inhomogeneous background and, because oscillons in non-relativistic collisions bounce or merge as a function of their relative phases, the outcomes of interactions between “wild” oscillons depend on their specific trajectories.
Read the full abstract

All authors Angela Xue, Kyle Chen, Baylee Verzyde, Peter Hayman, Richard Easther

Solar and Stellar Astrophysics

Orbital Period Changes of Recurrent Nova U Scorpii Demonstrate that M$_{\rm ejecta}$=26$\times$M$_{\rm accreted}$ and Is Not a Type Ia Supernova Progenitor

Bradley E. Schaefer and Gordon Myers

Recurrent nova U Scorpii (U Sco) is one of the prototypes for a Type Ia supernova progenitor. The logic is that the white dwarf is near the Chandrasekhar mass and gas is accumulating onto its surface at a near-maximal accretion rate, so it will soon increase its mass to the supernova trigger. But the white dwarf loses mass every nova eruption, so the issue is balancing the mass ejected ($M_{\rm ejecta}$) against the mass accreted between eruptions ($M_{\rm accreted}$). Measuring $M_{\rm accreted}$ can be done in several ways to useable accuracy. But the old methods for measuring $M_{\rm ejecta}$ (involving the flux in hydrogen emission lines) are all with real error bars of 2–3 orders of magnitude. The only solution is to measure the change of the orbital period across the nova eruption ($\Delta P$). But this solution requires a vast photometric program of eclipse timings stretching decades. For U Sco, a program started in 1989, now reaches its culmination with measures of $\Delta P$ for the eruptions of 1999, 2010, 2016, and 2022. This paper reports on 52 new eclipse times (for a total of 218 eclipses 1945–2025), plus a new theory result allowing for the confident calculation of $M_{\rm ejecta}$ from $\Delta P$. The four eruptions ejected a total of (103$\pm$14)$\times$$10^{-6}$ $M_{\odot}$, while the white dwarf accreted 4$\times$$10^{-6}$ $M_{\odot}$ over the four previous eruption cycles. With M$_{\rm ejecta}$=26$\times$M$_{\rm accreted}$, the U Sco white dwarf is losing large masses each eruption cycle, so U Sco can never produce a Type Ia supernova.
Read the full abstract

Solar and Stellar Astrophysics

Orbital Period Changes in Recurrent Nova T Corona Borealis Prove That It Is Not a Type Ia Supernovae Progenitor

Bradley E. Schaefer

T Corona Borealis (T CrB) is a recurrent nova and a symbiotic star that is commonly highlighted as the best case for being a progenitor of a Type Ia supernova (SNIa) within the framework of single-degenerate models. This exemplar can be tested by measuring whether the white dwarf (WD) mass ($M_{\rm WD}$) is increasing over each eruption cycle. This is a balance between the mass ejected during each nova event ($M_{\rm ejecta}$) and the mass accreted onto the WD between the nova events ($M_{\rm accreted}$). I have used all 206 radial velocities from 1946–2024 to measure the orbital period just after the 1946 eruption to be $P_{\rm post}$=227.6043 days, while the steady orbital period change ($\dot{P}$) is ($-$3.1$\pm$1.6)$\times$10$^{-6}$. I have used my full 213,730 magnitude $B$ and $V$ light curve from 1842–2025 to measure the times of maximum brightness in the ellipsoidal modulations to construct the $O-C$ from 1866–1946. I fit the broken parabola shape, to find the orbital period immediately before the 1946 eruption to be $P_{\rm pre}$=227.4586 days. The orbital period changed by $\Delta P$=$+$0.146$\pm$0.019 days. With Kepler's Law, conservation of angular momentum, and the well-measured binary properties, the ejecta mass in 1946 is 0.00074$\pm$0.00009 M$_{\odot}$. $M_{\rm accreted}$ is reliably measured to be 1.38$\times$10$^{-6}$ M$_{\odot}$ from the accretion luminosity. $M_{\rm ejecta}$ is larger than $M_{\rm accreted}$ by 540$\times$, so $M_{\rm WD}$ is decreasing every eruption cycle. T CrB can never become a SNIa.
Read the full abstract

High Energy Astrophysical Phenomena · Cross-listed from physics.plasm-ph

Suppression of inverse magnetic energy transfer in collisionless marginally magnetized plasmas

Zhuo Liu, Muni Zhou and Nuno F.G. Loureiro

We investigate the inverse cascade of magnetic energy in decaying, collisionless plasmas with moderate to high-$\beta$ values via first-principles numerical simulations and analytical theory. We find that pressure-anisotropy-driven instabilities, in particular the firehose instability, suppress reconnection-driven coalescence of magnetic structures (i.e., inverse transfer) by nullifying magnetic tension. This suppression leaves such structures elongated and confined to scales comparable to the Larmor radius of the particles. The presence of a magnetic guide field of sufficient strength, or a greater scale separation between the initial size of the magnetic structures and the Larmor radius, restores the system's ability to inverse transfer magnetic energy. These results reveal that inverse energy transfer in collisionless plasmas is not guaranteed, but instead sensitively depends on magnetization. In the astrophysical context, this identifies a kinetic mechanism by which Weibel-generated seed fields may fail to merge consistently, potentially limiting their role in cosmic magnetogenesis.
Read the full abstract