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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 7 July

Instrumentation and Methods for Astrophysics

Exploring Image-Text Alignment for Radio Galaxy Morphologies

Erica Lastufka, Mariia Drozdova and Svyatoslav Volosynovskiy

We investigate whether specially constructed text captions can capture the same morphological information as radio galaxy images. Using the MiraBest dataset, we generate captions with a domain-specific prompt and evaluate their alignment with images through the SigLIP-2 vision–language model, with and without LoRA fine-tuning. Results show that caption-based classification of FR-I and FR-II galaxies performs similarly to images, with fine-tuning improving local coherence of embeddings but not global alignment.
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High Energy Astrophysical Phenomena

Chandra X-Ray Imaging and Spatially Resolved Spectroscopy of SN 1987A: Energy-Dependent Morphology of the Equatorial Ring

Yusuke Sakai, Shinya Yamada, Koji Mori et al. (+8 more)

We present a systematic imaging and spatially resolved spectral study of SN 1987A using Chandra observations obtained between 1999 and 2025. By combining multiepoch ACIS and HETG data, we investigate the long-term evolution of the remnant in both the soft and hard X-ray bands. To characterize the radial structure, we model the projected emission with a torus profile and derive its radius and width on the image plane. We find an energy dependence in the ring morphology: while the soft and hard bands exhibit similar structures at early epochs, the soft-band emission becomes systematically broader than the hard-band emission after the early 2010s. Furthermore, when considering the radius and width together, the soft-band emission shows an inward extension, suggesting an increasing contribution from interior and/or high-latitude emission components. The flux evolution of the Fe K line is consistent with previous XMM-Newton results, and we detect its presence already in earlier epochs (~2007-2009) using combined Chandra spectra. Spatially resolved analysis further indicates that the Fe K emission is enhanced in the eastern region. These results provide a unified view of the long-term morphological and spectral evolution of SN 1987A and highlight the emergence of energy-dependent radial structure as a key feature in its late-time evolution.
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All authors Yusuke Sakai, Shinya Yamada, Koji Mori, Hiromasa Suzuki, Haruka Sakemi, Tsukasa Matsushima, Shintaro Kaneko, Kai Matsunaga, Shogo B. Kobayashi, Haruto Aoki, Toshiki Sato

Earth and Planetary Astrophysics

Implications of a Stable Layer on the Vertical Structure of Jet Streams on Jupiter

Keren Duer-Milner, Louis Siebenaler, Lillian Haley et al. (+1 more)

The vertical structure of Jupiter's jet streams remains a critical open question for understanding the planet's atmospheric dynamics and interior. Traditional models often assume an adiabatic density profile, yet recent observations and theory suggest the presence of stable layers, which could significantly alter both the density structure and gravitational signature. We investigate the implications of non-adiabatic stable layers for Jupiter's gravity field, focusing on how density anomalies from such layers interact with the inferred vertical structure of zonal winds. We construct temperature-pressure profiles including subadiabatic stable layers to derive density profiles consistent with the latest equation of state. The resulting gravitational harmonics are computed, incorporating both static density and wind structure via thermal wind balance, and compared with Juno measurements. By varying the wind decay characteristics, we assess how stable layers constrain the depth and structure of the deep jets. Our results show that shallow, extensive stable layers substantially modify the background density, requiring more rapid decay of zonal winds to satisfy observed gravitational constraints. Introducing stable layers also broadens the range of physically plausible wind solutions, inadicating that the vertical structure of the jets is less constrained than suggested by purely adiabatic models. We conclude that stable layers are a critical, yet often overlooked, component in modeling Jupiter's interior and dynamics. This study highlights a strong degeneracy between the thermodynamic density structure and the vertical wind profile, implying that the jet stream structure cannot be uniquely determined without independent constraints on the planet's internal stability.
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All authors Keren Duer-Milner, Louis Siebenaler, Lillian Haley, Yamila Miguel

Earth and Planetary Astrophysics

The Cost of Lunar South-Polar Geometry, and Surface Beacons as the Efficient Fix: A Dilution-of-Precision Analysis

Chakshu Baweja

Lunar PNT architectures, NASA's Lunar Augmented Navigation Service (LANS), ESA's Moonlight, and allied concepts, place a small number of satellites in elliptical lunar frozen orbits (ELFO) to serve the south-polar region prioritized for exploration. We report a result that reframes the design trade: for a user at the lunar south pole, the satellite count needed to reach good geometry is roughly double what is currently planned, because the visible satellites cluster into a small solid angle overhead and dilution of precision is limited by their angular spread rather than their number. In a time-averaged simulation, orbit-only ELFO constellations of the planned size (4 to 6 satellites) give a south-polar median geometric DOP (GDOP) of 16 to 21, far worse than the GDOP of about 6 routine for terrestrial GNSS, and the constellation must grow to about 12 satellites before the median GDOP crosses 6. We then show that a small number of surface ranging beacons, a configuration absent from the lunar PNT literature, reaches the same geometric quality far more cheaply by supplying the near-horizon diversity the overhead cluster lacks: three beacons on elevated terrain around a -80 deg latitude user cut the median GDOP from 16.2 to 1.6, a factor of about 10, moving the user from 15% to 100% of the time below GDOP 6, geometry a purely orbital solution reaches only near a 24-satellite fleet. Because there is no atmospheric refraction, surface-to-surface line of sight is bounded by the geometric horizon, so beacon siting on crater rims and elevated terrain is itself a design variable. Surface-beacon augmentation is the lowest-cost, highest-leverage improvement available to lunar south-polar PNT, deployable on assets already planned for the region. The geometry engine is Validated against an independent DOP computation; the constellation and beacon scenario are Modelled.
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High Energy Astrophysical Phenomena

An intrinsic decline of accretion activity in GRS 1915+105

Poshak Gandhi and Peter G. Boorman

The canonical microquasar GRS 1915+105 is exhibiting unprecedented changes in its multiwavelength properties since 2018. Recent pointed observations with NuSTAR in November 2025 have failed to detect the source at flux limits several orders of magnitude deeper than historical X-ray levels. Under an enhanced obscuration scenario, the absence of hard X-rays requires that any obscuring cocoon must be deeply Compton-thick and fully sky covering, with a stringent limit on scattering fractions being less than 1 part in >~10^4, if intrinsic accretion activity continues unabated. An ionised cocoon could also account for a deep radio non-detection in June 2026. But such an interpretation is in conflict with mid-infrared fading of the source observed with SPHEREx in September 2025 and then again in April/May 2026. These facts, together with the source location in the infrared vs. X-ray plane, are consistent with an intrinsic weakening of accretion activity around November 2025 or earlier. We propose that outflows witnessed during intense multiwavelength flaring in 2023-2024 have progressively expelled fueling material from the inner disc, resulting in a significant drop in accretion activity. If correct, the current state gives unique insight into ongoing dramatic secular accretion changes on human timescales. High-frequency resolved radio observations and sensitive infrared or sub-mm observations could test this scenario, and characterise any gaseous cocoon still veiling the source.
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High Energy Astrophysical Phenomena

The X-ray Variability of the Ultraluminous X-ray Sources in the NGC 4631 galaxy

Jiashun Chen, Jianfeng Wu and Zikun Lin

We perform a systematic study on the long-term X-ray variability for the five ultraluminous X-ray sources (ULXs) in the NGC 4631 galaxy (X1-X5), using Chandra, XMM-Newton, and Swift observations covering a 24-year span. Light curves for the five ULXs are presented, while X-ray spectra were modeled for observations with sufficient counts. The normalized excess variance and structure function are utilized to study the X-ray variability behavior of the ULXs. The normalized excess variance is anti-correlated with average X-ray luminosity for three ULXs, indicating that objects with higher average luminosity tend to exhibit relatively lower amplitude of variability. The structure function values increases with time interval in two sources, showing that flux variations become more significant for longer timescales. These trends are also found in the X-ray variability of active galactic nuclei (AGNs). The similarity between ULXs and AGNs, if confirmed for a larger sample of sources, possibly indicates similar underlying physical mechanisms for their X-ray variability.
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High Energy Astrophysical Phenomena

Pulsars in Globular Clusters With the SKAO

M. Bagchi, F. Abbate, V. Balakrishnan et al. (+14 more)

Globular clusters (GCs) are highly efficient factories of radio pulsars: per unit of stellar mass, they contain about 1000 times more pulsars than in the Galactic field. Thus far, 345 radio pulsars have been found in GCs. These can be used as precision probes of the structure, gas content, magnetic field, and dynamic history of their host clusters; some of them are also highly interesting in their own right because they probe exotic stellar evolution scenarios, the physics of dense matter, accretion, gravity, etc. One of them (PSR~J0514$-$4002E) might even be the first pulsar - black hole system known. Deep searches with SKA telescopes will only require one to a few tied-array beams, and can be done during early commissioning of the telescopes, before an all-sky pulsar survey using hundreds to thousands of tied-array beams is feasible. Even a conservative approach predicts discoveries only with the core of SKA-MID AA*. Eventually, SKA-MID AA4 is expected to increase the number of discoveries even more, leading to more than doubling the current known population. Thus, a dedicated search for pulsars in GCs will fully utilise the best possible natural laboratories to study various branches of physics and astrophysics, including the properties of dense matter, stellar evolution, and the dynamical history of these GCs.
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All authors M. Bagchi, F. Abbate, V. Balakrishnan, M. C. i Bernadich, B. Bhattacharyya, A. Dutta, P. C. C. Freire, K. Halley, J. W. T. Hessels, S. Kumari, D. R. Lorimer, A. Possenti, R. Nag, S. M. Ransom, A. Ridolfi, V. Venkatraman Krishnan, W. W. Zhu

Cosmology and Nongalactic Astrophysics

Imprint of swampland-inspired coupled early dark energy

Hao Wang and Yun-Song Piao

Inspired by the Swampland Distance Conjecture, we investigate the cosmological implications of a fractional coupling between dark matter (DM) and early dark energy (EDE) in light of the recent DESI DR2 BAO data. We use a conditional normalizing flow network to efficiently sample the high-dimensional parameter space, and perform a joint analysis of Planck CMB data, DESI DR2 BAO, PantheonPlus supernovae and SH0ES. We find that the detailed construction of the EDE potential beyond the mere existence of an EDE component possibly alter cosmological constraints on late-time dark energy when the coupling between DM and EDE is considered.
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Astrophysics of Galaxies

Deep far-UV observations of the ELAIS N1 field using AstroSat: Source catalogue, spectral energy distribution modelling and star formation

Pranjal Chaturvedi, Akriti Sinha, Abhirup Datta et al. (+1 more)

We present a far-ultraviolet (FUV) photometric study of the ELAIS N1 deep field using the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat, observed in the F154W filter ($\lambda_{\rm eff} = 1541$\,Å) with a total on-source exposure time of 30\,ksec. Level 1 data were reduced using CCDLAB v3.0, yielding source catalogues of 1637 objects at $3\sigma$ and 458 objects at $5\sigma$, with limiting magnitudes of $25.69\,m_{AB}$ and $25.13\,m_{AB}$ respectively. FUV positions are cross-matched against multiwavelength catalogues spanning optical and infrared wavelengths, with redshifts drawn from spectroscopic and photometric sources. Active galactic nuclei (AGN) are identified and excluded via established multiwavelength criteria, leaving a clean sample of star-forming galaxies (SFGs). Spectral energy distribution (SED) modelling is performed using CIGALE, employing a delayed star formation history with an optional late burst, Bruzual & Charlot stellar population synthesis, Calzetti dust attenuation, and the SKIRTOR AGN module. From the best-fit models, we derive star formation rates (SFRs), total stellar masses, and young stellar masses as a function of redshift. The SFR increases monotonically with redshift, consistent with the evolution of the Star Formation Main Sequence (SFMS). The ratio of young-to-total stellar mass remains approximately constant across $0 < z \lesssim 0.76$, confirming that the sample consists predominantly of secularly evolving systems undergoing steady, self-regulated star formation rather than starburst-driven episodes.
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All authors Pranjal Chaturvedi, Akriti Sinha, Abhirup Datta, Kanak Saha

Cosmology and Nongalactic Astrophysics

Executable verification through formalized expert reasoning in astronomical spectroscopy

Haosong Wang, Ting Tan, Ji Yao et al. (+5 more)

Artificial intelligence has reshaped scientific prediction, but scientific verification remains a human bottleneck. Automated systems can map observations to labels, parameters or hypotheses, yet scientific conclusions require evidence, must satisfy physical consistency, and need explicit testing of alternatives before a decision is made. Here we introduce FORMA (Formalized Observational Reasoning with Auditable Decisions), an executable verification protocol that reconstructs expert reasoning into a workflow: it extracts evidence, generates hypotheses under physical constraints, tests alternatives, and performs auditable consistency checks. Unlike prediction or post-hoc interpretability, executable verification records and tests the evidential path leading to a decision. Astronomical spectroscopy provides a natural testbed, because ambiguous survey spectra are still adjudicated by expert visual inspection. Applied to the Dark Energy Spectroscopic Instrument (DESI) visual inspection catalogue, FORMA combines template-fitting candidate redshifts, spectral evidence extraction and physical audit into an auditable credibility score. A medium-or-higher credibility threshold identifies $331$ definite predictions with $95.5\%$ binary agreement with expert-adjudicated classes, while increasing credibility is associated with improved redshift consistency and higher classification reliability. These results show that automated inference can be coupled to explicit verification, allowing candidate outputs to be evaluated before they enter scientific use.
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All authors Haosong Wang, Ting Tan, Ji Yao, Jiajun Zhang, Qian Zheng, Christophe Yeche, Jean-Paul Kneib, Huanyuan Shan

Solar and Stellar Astrophysics

Refined reduction and standardisation of 53 years of UBV photometry at Hvar

Hrvoje Božić, Petr Harmanec, Miroslav Brož et al. (+17 more)

Emission-line stars classified as Be exhibit light and colour variability on various timescales, ranging from days to decades. Their evolution must be constrained by long-term observations that are accurately calibrated and stable. Here, we provide a new reduction of photoelectric UBV observations obtained at the Hvar observatory, spanning more than 50 years. This unique dataset is highly complementary to TESS. We used new, non-linear reduction equations, with temporally variable extinction over the course of the night, which allowed us to achieve long-term accuracy of 0.008 to 0.016 mag (1-sig uncertainty), as verified by the Johnson standards. We then classified 59 Be stars into five classes, based on their variability patterns; namely, long-term envelope (LTE), long-term cyclic (LTC), binarity (BIN), rapid low-amplitude (RLA), and long-term quiescence (LTQ). According to our observations, the percentages of stars in the individual classes are 44%, 24%, 25%, 66%, and 19%, respectively. The stars in the sample often exhibited more than one pattern. We confirm that the LTE-positive variability is more common than the inverse (20 vs 6); in addition, two stars exhibited both types (zeta Tau and V1294 Aql). According to our observations, the LTC variability and the LTE-positive variability are almost mutually exclusive. Among 26 binary systems, circular orbits are more common than eccentric ones (18 vs 8). As for the brightness variations between different quiescent phases, an increasing trend is less common than a decreasing one (4 vs 7), spanning from -6.5 to +6.0 mmag/yr. Our observations provide well-calibrated UBV light curves spanning several decades, offering a valuable dataset for investigations of Be-star variability and tests of various models, including the viscous decretion disc model. Continuous monitoring is important for beta Lyr, EW Lac, delta Sco, gamma Cas, and V1294 Aql.
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All authors Hrvoje Božić, Petr Harmanec, Miroslav Brož, Alžběta Oplištilová, Pavel Koubský, Petr Hadrava, Domagoj Ruždjak, Davor Sudar, Marek Wolf, Petr Zasche, Jaroslav Honsa, František Žďárský, Adam Harmanec, Juraj Jonák, Isabell Piantschitsch, Ivica Skokić, Jana Švrčková, Kristián Vitovský, Donik Vršnak, Michal Zummer

High Energy Astrophysical Phenomena

A Possible Triple Formation Scenario of Binary Black Hole Merge With One In Pair-instability Supernova Mass Gap

Tian Huang, Xizhen Lu, Guoliang Lü et al. (+8 more)

Observations of binary black hole (BBH) mergers detected by LIGO – such as GW170729, GW190620, GW190706, GW230107, GW230820, and GW230928 – feature high effective spins and primary black holes that fall squarely into the pair-instability supernova (PISN) mass gap ($\sim 45-130 \, M_{\odot}$). These events pose a significant challenge to standard stellar and binary evolution theories. To address this, we propose an isolated hierarchical triple stellar evolution channel. In this framework, tidal synchronization in tight inner binaries drives chemically homogeneous evolution (CHE), entirely bypassing giant expansion. A subsequent triple common envelope (TCE) evolution, triggered by the tertiary companion, rapidly drives the inner BBH to coalescence. Our model can provide a detailed evolutionary pathway that elegantly reproduces the properties of these GWs, such as GW190706. Assuming a low-metallicity environment ($Z = 0.001$), our framework predicts a volumetric merger rate of approximately $0.011 \, \mathrm{Gpc}^{-3}\mathrm{yr}^{-1}$ at $z \approx 0.68$, accounting for $22\%$ of the empirical rate for this mass regime in the GWTC-4 catalog. This study demonstrates that primordial triple interactions are a highly efficient avenue for populating the PISN mass gap.
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All authors Tian Huang, Xizhen Lu, Guoliang Lü, Chunhua Zhu, Sufen Guo, Helei Liu, Zhuowen Li, Zhijun Wang, Lei Li, Wei-Min Gu, Nurzada Beissen

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

Background-independent one-loop renormalization of tensor and scalar primordial spectra

Guillermo Ballesteros, Jesús Gambín Egea and Flavio Riccardi

We present a background-independent renormalization framework for one-loop primordial spectra. We apply it to two observables: the scalar-induced tensor spectrum sourced by a minimally coupled spectator field, and the scalar spectrum generated by potential self-interactions. In both cases, the UV part of the loops is isolated and, using the universal WKB behavior of the internal modes, the UV poles are extracted analytically and absorbed into local counterterms without having to specify either the background evolution or the full dynamics of the field running in the loop. This yields finite model-independent expressions for the renormalized spectra amenable to numerical analysis.
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High Energy Astrophysical Phenomena

The problem of escape: a missing bit in the theory of the origin of cosmic rays

P. Blasi and E. Amato

The escape of cosmic rays from their sources, as well as from the region surrounding a source, or from the galaxy hosting the sources, is a non-linear process that involves a complex chain of events, often overlooked. On the other hand, these phenomena are responsible for setting the maximum energy in accelerators, shaping the source spectra and determining the conditions for escape from the galaxy hosting the sources, a process that is usually modeled by imposing ad hoc boundary conditions in our equations. Here we discuss some of these phenomena and how they affect the spectra of cosmic rays measured at the Earth.
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Astrophysics of Galaxies

A Face-on View of Interstellar Dust in the Galactic Plane

Lin Zhang, Bingqiu Chen, Fei Qin et al. (+3 more)

Interstellar dust is a fundamental component of the Milky Way, influencing star formation, galactic evolution, and observations across the electromagnetic spectrum. Using red clump stars selected from near- and mid-infrared photometry, together with stellar catalogs from previous studies, we construct dust density maps of the Galactic plane ({$|Z|<25$}\,pc) covering the full $360^\circ$ in longitude and reaching distances up to $7$\,kpc. By applying a U-Net convolutional neural network to invert the line-of-sight extinction distribution, we obtain dust density maps at resolutions of $10$, $50$, and $100$\,pc, which reveal detailed structures including spiral arms, inter-arm spurs, and giant cavities. The dust distribution in the Galactic plane exhibits a morphology closely resembling that of the so-called Phantom galaxy M74. The derived exponential scale length of the Galactic dust disk is $2.90$\,kpc, slightly larger than that of the stellar thin disk. Our publicly available dust maps provide a new benchmark for extinction correction, studies of Galactic structure, and the investigation of the interplay between star formation and the interstellar medium.
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All authors Lin Zhang, Bingqiu Chen, Fei Qin, Guangxing Li, Haibo Yuan, Yi Ren

Solar and Stellar Astrophysics

Investigating white-light flare mechanisms via the Paschen jump using high-resolution continuum observations from the Swedish 1-m Solar Telescope

Sascha Ornig, Luc Rouppe van der Voort, Mats Carlsson et al. (+4 more)

The continuum is understood to contain a large portion of the energy emitted by a solar flare. The optical continuum, known as white light (WL), is particularly relevant since it may be observed by ground-based instruments. We measured the WL enhancements short- and longward of the Paschen jump in order to gain insights into the possible mechanism(s) behind the creation of these increases in our two case studies. We took measurements from the Swedish 1-m Solar Telescope of the pseudo-continuum around the Ca II 8542 Å line as well as the true continuum around the K I 7699 Å and the Fe I 6173 Å line, providing us with observations on both sides of the Paschen jump. We observe WL enhancements of over 40% against the dark (pen-) umbral background in both flares. The WL excess in flare 1 is co-temporal with the derivative of the GOES soft X-ray and hard X-ray (HXR) measurements from the Advanced Space-based Solar Observatory (ASO-S), and the flare is compatible with the Neupert effect. For flare 2, a preceding smaller flare may be the cause of the temporal discrepancy. Signatures of chromospheric evaporation and condensation are found in the WL area for both flares. The ratio of intensities blueward and redward of the Paschen jump in flare 1 is below one for most WL pixels. This is in disagreement with the accepted WL formation mechanisms. We believe this is a consequence of the Ca II 8542 Å pseudo-continuum being affected by line wing opacity changes. The co-temporality of WL and HXR enhancements suggests that the WL emission enhancements in flare 1 (and parts of flare 2) are a result of direct electron precipitation. We conclude that more reliable continuum measurements free of any nearby line influence are necessary in order to obtain conclusive evidence for the formation mechanism(s) behind optical continuum enhancements from such analysis as presented in this work.
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All authors Sascha Ornig, Luc Rouppe van der Voort, Mats Carlsson, Carlos José Díaz Baso, Eilif Sommer Øyre, Ignasi Josep Soler Poquet, Aline Rangøy Brunvoll

Solar and Stellar Astrophysics

TESS light curves and surface activity in two low-mass eclipsing binaries: NSVS 01031772 and 2MASS J04100497+2931023

Marek Wolf, Ladislav Šmelcer, Hana Kučáková et al. (+7 more)

The VRIC light curves were regularly measured for two eclipsing binaries, NSVS 01031772 and 2MASS J04100497+2931023 as part of our long-term observational project to study low-mass eclipsing binaries with a short orbital period and surface activity. The solution of the TESS light curves in PHOEBE results in a detached configuration. Absolute parameters of all components were improved: for N103: M1 = 0.5475 +/- 0.0035 M\sun, R1 = 0.5297 +/- 0.0035 R\sun, M2 = 0.5038 +/- 0.0040 M\sun, R2 = 0.5217 +/- 0.0035 R\sun, for 2M0410: M1 = 0.639 +/- 0.045 M\sun, R1 = 0.655 +/- 0.035 R\sun, M2 = 0.609 +/- 0.045 M\sun, R2 = 0.631 +/- 0.035 R\sun, where the temperatures of the primary components were adopted according to previous studies. The spectral type of the primary components was confirmed to be M4 and K5, and the mass ratio was derived as q = 0.920 +/- 0.003 or 0.952 +/- 0.010, respectively. We propose the presence of a third body in these systems: in the case of N103, a companion with a minimal mass of 50 MJup, orbiting the eclipsing pair with a period of about 19 years, and in 2M0410 a third body with a minimal mass of about 0.1 M\sun and a short orbital period of about 2.1 years. For N103, the hierarchical structure (2+1)+1 of a possible quadruple system was tested, but its stability was not proven. The characteristics and statistics of the flare events and dark regions on the surface of the components were estimated on the basis of the TESS and our own data. For N103, a mean frequency of flares of one per 40 hours was determined. In the case of 2M0410, practically no flares were detected.
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All authors Marek Wolf, Ladislav Šmelcer, Hana Kučáková, Alžběta Oplištilová, Petr Zasche, František Bílek, Andrej Mudray, Tomáš Hynek, Miloslav Zejda, Kamil Hornoch

High Energy Astrophysical Phenomena

Two fluid CFL strange quark stars with scalar dark matter: critical mass and mass gap implications

J. Sedaghat, G. H. Bordbar, M. Haghighat et al. (+1 more)

We investigate the structure of strange quark stars (SQSs) in the color–flavor–locked (CFL) phase in the presence of scalar bosonic dark matter within a two–fluid formalism employing perturbative QCD. By considering different dark matter masses and varying the pairing gap $\Delta$ and {the central dark matter pressure fraction} $f_r$, we analyze the impact of dark matter on the structural properties of SQSs, including the maximum gravitational mass $M_{\mathrm{TOV}}$, the ratio of dark matter to strange-quark-matter radii $R_{\mathrm{DM}}/R_{\mathrm{SQM}}$, and the dimensionless tidal deformability $\Lambda$. We further examine the compatibility of the resulting mass–radius relations with the recent NICER measurements of compact stars. Within the parameter space considered in this study, we find that $M_{\mathrm{TOV}}$ exhibits a non-monotonic dependence on the dark matter mass, with a critical value beyond which $M_{\mathrm{TOV}}$ decreases. We also show that some pure CFL strange quark star configurations, particularly those associated with very stiff EOSs and larger maximum masses, may not simultaneously remain compatible with the $\Lambda$ range inferred from GW170817 while occupying the lower mass–gap region. In contrast, the inclusion of dark matter allows two-fluid CFL strange quark star configurations to reproduce the observed properties of massive compact objects in the lower mass–gap region, such as the secondary component of GW190814, while remaining qualitatively compatible with the $\Lambda$ range inferred from GW170817. We note, however, that the GW170817 constraints were originally inferred within single-fluid compact-star frameworks and therefore provide only {qualitative guidance} for the present two-fluid halo configurations. Our results suggest that exotic compact-star configurations may populate part of the conventionally defined lower mass–gap region.
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All authors J. Sedaghat, G. H. Bordbar, M. Haghighat, S. M. Zebarjad

High Energy Astrophysical Phenomena

Identifying a circum-jet southern ring counterpart to the northern jet of the Crab Nebula

Noam Soker

I analyze images of the Crab Nebula core-collapse supernova (CCSN) remnant in light of recent three-dimensional hydrodynamical simulations of the jittering-jets explosion mechanism (JJEM) and identify a southern ring opposite to the northern jet, which I attribute to a counterjet. The Crab Nebula is known for its point-symmetric morphology of seven pairs of bays and a pair of two filaments, but no pairs of two jets or their direct outcomes, like ears and rings, have been identified. I identify a ring in visible and infrared images of the Crab Nebula opposite to the prominent northern jet. Recent hydrodynamical simulations of the JJEM show that jets that explode CCSNe can form such circum-jet rings. I, therefore, attribute the shaping of the southern ring to a southern jet, a counter jet to the northern jet, both of which participated in the explosion of the Crab Nebula in the framework of the JJEM.
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High Energy Astrophysical Phenomena

Unveiling the Local Environment of FRB 20220912A: Sub-arcsecond $4-26$ GHz Radio Continuum Mapping

Yash Bhusare, Yogesh Maan, Mohit Bhardwaj et al. (+4 more)

The local environments of repeating fast radio bursts (FRBs) provide critical clues to their progenitors. While some active repeaters (e.g., FRB~20121102A, FRB~20190520B) are embedded in compact persistent radio sources (PRS), others appear to reside in cleaner environments. We present a high-resolution, multi-frequency (4$-$26 GHz) continuum study of the hyperactive repeater FRB 20220912A using the Karl G. Jansky Very Large Array (VLA). We report the discovery of a previously unknown radio source distinct from the compact PRSs seen in other FRBs, spatially coincident with the FRB position and offset by $\approx 300$~mas ($\approx 450$~pc) from the host galaxy's center. The absence of continuum emission in archival milliarcsecond-resolution VLBI observations indicates that the source is resolved out, ruling out a hyper-compact ($< 1$~pc) central-engine-powered origin. We constrain the physical diameter of the emitting region between 75~pc and 190~pc. We further demonstrate that the source is characterized by a steep non-thermal spectral index ($\alpha \approx -0.73$) and a remarkably high star-formation rate surface density $\Sigma_{\text{SFR}} \gtrsim 13~M_{\odot}~\text{yr}^{-1}~\text{kpc}^{-2}$. We argue that this emission is best explained as a compact star-forming region within the host galaxy. This association with a site of ongoing star formation provides strong observational support for the hypothesis that young magnetars, formed after the deaths of massive stars, are the progenitors of at least some repeating FRBs.
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All authors Yash Bhusare, Yogesh Maan, Mohit Bhardwaj, Thomas C. Abbott, Yuxin Dong, Danté M. Hewitt, Afrokk Khan

High Energy Astrophysical Phenomena

Multi-messenger View of White Dwarf Tidal Disruption Events by Intermediate-Mass Black Holes: I. Gravitational Waves and Disk Photon and Neutrino Emissions

Jin-Hong Chen, Lixin Dai and Bing Zhang

White dwarf (WD) tidal disruption events (TDEs) provide a unique window onto intermediate-mass black holes (IMBHs). We present a multi-messenger view of these systems in two papers. In this paper, we develop an accretion-disk model for WD–TDEs in which the bound debris accretes at extremely super-Eddington rates, $\sim 10^5$–$10^9$ times higher than in typical (main-sequence) TDEs. The model includes magnetic pressure, nuclear-burning heating, wind mass loss, and neutrino production via $e^{\pm}$ pair annihilation. At such high accretion rates, the gas and radiation temperatures of the inner flow can reach $T\gtrsim 10^9\,\mathrm{K}$, enabling prolific pair production and MeV neutrino emission. We find that the disk is predominantly advection dominated over a broad range of accretion rates, while disk winds can partially cool the flow and reduce the inner temperature. The predicted thermal EM emission is nearly insensitive to the fallback rate in the super-Eddington regime: the luminosity only mildly exceeds the IMBH Eddington luminosity and the spectrum peaks at $\sim 0.1$–$1\,\mathrm{keV}$, implying detectability with current X-ray facilities such as Einstein Probe. For low-mass IMBHs ($\sim 10^3\,M_{\odot}$), the disk can also produce a burst of MeV neutrinos with luminosities up to $\sim 10^{47}\,\mathrm{erg\,s^{-1}}$ for ONeMg WD–TDEs, although detectability with current neutrino detectors (e.g., Super-Kamiokande and JUNO) is limited to Galactic distances. Finally, we estimate the GW burst produced during the final passage prior to disruption, which peaks at $\sim 0.1$–$1\,\mathrm{Hz}$, placing WD–TDEs in the target band of proposed decihertz detectors and motivating coordinated GW+EM+neutrino searches. We also present a first exploration of GWs from a precessing WD–TDE disk; this signal is much weaker, with a detection horizon $\lesssim 1\,\mathrm{Mpc}$ for these missions.
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Cosmology and Nongalactic Astrophysics

CMB Lensing Reconstruction Using Two Years of Temperature Data from the SPT-3G Summer Survey

K. Levy, S. Raghunathan, F. Guidi et al. (+91 more)

We present the first reconstruction of the cosmic microwave background (CMB) lensing potential from the SPT-3G Summer survey using two years of temperature data. The Summer survey has a total area of approximately 2640 deg$^2$, split into three fields covering 1210, 570, and 860 deg$^2$, respectively. A joint analysis of the three Summer fields yields a lensing amplitude of $A^{\rm comb} = 1.015 \pm 0.053$ relative to a fiducial Planck 2018 $\Lambda$CDM cosmology for the multipole range $50 < L < 2000$. These early results from the SPT-3G Summer survey highlight the potential for increasing the signal-to-noise ratio when combining the Summer fields with the SPT-3G Main and Wide fields for a total SPT-3G survey area of $\sim$ 10,000 deg$^2$.
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All authors K. Levy, S. Raghunathan, F. Guidi, Y. Li, E. Anderes, A. J. Anderson, B. Ansarinejad, M. Archipley, L. Balkenhol, D. R. Barron, K. Benabed, A. N. Bender, B. A. Benson, F. Bianchini, L. E. Bleem, S. Bocquet, F. R. Bouchet, E. Camphuis, M. G. Campitiello, J. E. Carlstrom, J. Carron, C. L. Chang, P. M. Chichura, A. Chokshi, T.-L. Chou, A. Coerver, T. M. Crawford, C. Daley, T. de Haan, K. R. Dibert, M. A. Dobbs, M. Doohan, D. Dutcher, C. Feng, K. R. Ferguson, N. C. Ferree, K. Fichman, A. Foster, S. Galli, A. E. Gambrel, A. K. Gao, F. Ge, S. Guns, N. W. Halverson, E. Hivon, G. P. Holder, W. L. Holzapfel, J. C. Hood, A. Hryciuk, N. Huang, T. Jhaveri, F. Kéruzoré, A. R. Khalife, L. Knox, K. Kornoelje, C.-L. Kuo, A. E. Lowitz, C. Lu, G. P. Lynch, T. J. Maccarone, A. S. Maniyar, E. S. Martsen, F. Menanteau, M. Millea, J. Montgomery, Y. Nakato, T. Natoli, A. Ouellette, Z. Pan, P. Paschos, K. A. Phadke, A. W. Pollak, K. Prabhu, W. Quan, M. Rahimi, A. Rahlin, C. L. Reichardt, M. Rouble, J. E. Ruhl, A. C. Silva Oliveira, A. Simpson, J. A. Sobrin, A. A. Stark, J. Stephen, C. Tandoi, C. Trendafilova, J. D. Vieira, A. G. Vieregg, A. Vitrier, Y. Wan, N. Whitehorn, W. L. K. Wu, M. R. Young, J. A. Zebrowski

High Energy Astrophysical Phenomena

Dependence of Particle Acceleration Efficiency on Shock Velocity in Weakly Magnetized Electron-Ion Shocks

Taiki Jikei, Daniel Groselj and Lorenzo Sironi

Using unprecedentedly long 2D particle-in-cell simulations, we study electron and ion acceleration in weakly magnetized quasi-parallel shocks, propagating at velocities ranging from transrelativistic to subrelativistic. At a fixed upstream magnetic field strength, low-velocity quasi-parallel shocks are dominated by the Bell instability, whereas high-velocity shocks are dominated by the Weibel instability. Both regimes accelerate ions with similar efficiency, with the Bell-dominated regime exhibiting faster growth in the maximum particle energy. The electron acceleration efficiency is strongly dependent on shock velocity. Weibel-dominated shocks have $\sim15\,\%$ of shock energy in nonthermal electrons, whereas in the Bell-dominated regime we attribute less than $\sim2\,\%$ of shock energy to nonthermal electrons. We discuss applications of our results to the bright X-ray emission from the late-stage afterglows of gamma-ray bursts, the radio emission from fast blue optical transients, and the X-ray variability in microquasars.
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Monday 6 July

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

Beyond {\Lambda}CDM with the SKA Observatory – I: Probing Gravity on Cosmological Scales

S. Camera, C. Addis, S.L. Guedezounme et al. (+26 more)

General relativity (GR) is currently the best description of the gravitational interaction at our disposal and is one of the foundations of the concordance cosmological model. For as much as we know that GR is not the final theory of gravitation - we still lack an understanding of its fundamental, quantum nature - it has demonstrated a remarkable success in describing observed phenomena and predicting effects that have later been confirmed by laboratory experiments or astronomical observations. Since gravity is extremely weak compared to the other three fundamental interactions, it has so far been tested with exquisite precision only in the strong-field regime. On the immense scales of the cosmos, on the other hand, the gravitational field is extremely weak and spacetime curvature is almost negligible. But crucially, it is on these scales that we see hints at the need for exotic components, such as dark matter and dark energy. The question of whether they really exist or their presence is but an artefact of the incompleteness of our understanding of gravity on cosmological scales then naturally arises. It is therefore paramount to test the validity of GR on these scales, either to further confirm its robustness or to detect deviations that could lead us to the formulation of a more general and conclusive theory of gravitation. To this purpose, the SKA Observatory is especially suited, thanks both to the enormous volumes it will probe, and to the variety and complementarity of cosmological observables that its surveys will make available to us.
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All authors S. Camera, C. Addis, S.L. Guedezounme, F. Montano, T. Montandon, M. Novara, S.J. Rossiter, J. Asorey, S. Castello, C. Clarkson, J. Fonseca, N. Frusciante, C. Gomes, N.Grimm, A. Nasirudin, L.G.T.Oliveira, F. Pace, Z. Sakr, M. Berti, C. Bonvin, P. Bull, E. Di Dio, C. Cress, C. Heneka, H.-R. Kloeckner, R. Maartens, C.J.A.P. Martins, D. Parkinson, C.S. Saraf

Solar and Stellar Astrophysics

Hints of enhanced magnetic activity after the intermediate rotation period gap as traced by the chromospheric Ca ii infrared triplet

Diego Godoy-Rivera, Savita Mathur, Tyler Richey-Yowell et al. (+5 more)

For low-mass stars (M < 1.4 Msun), the connection between stellar rotation and magnetic activity governs stellar spin-down, shapes the environments of their exoplanets, and provides an age-diagnostic via magneto-gyro-chronology. Recently, unexpected phenomena known as the intermediate rotation period gap and the rotational stalling have been discovered. These are likely due to internal angular momentum redistribution, and mark departures from a smooth spin-down evolution. These features have been shown to cause enhanced magnetic activity on the photosphere, as measured by the photometric index from light curves (Sph), in both cluster and field stars. However, their influence on other magnetic activity proxies, and particularly in field stars, remains poorly understood. In this work, we study the impact of the intermediate-period gap on chromospheric magnetic activity as traced by the Ca ii infrared triplet (IRT) index. We target the stars observed by the Kepler mission, as this is the largest and most reliable sample of field stars with measured rotation periods sensitive to the gap. We calculate the Ca ii IRT index for the Kepler stars using the spectroscopic information from the Gaia mission data release three (DR3). We study the rotation-activity relation as a function of spectral type, finding that K dwarfs are more active than G dwarfs, which in turn are more active than F dwarfs. For main-sequence stars, we find that chromospheric magnetic activity is also enhanced after the intermediate-period gap, mirroring its effect on the photospheric Sph index. Our work reveals that the intermediate-period gap marks a genuine transition in stellar magnetic behavior, not only at the photosphere but also at the chromosphere. This highlights the need to account for its signatures across activity proxies, as well as its impact on exoplanet habitability and the age-rotation-activity relation.
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All authors Diego Godoy-Rivera, Savita Mathur, Tyler Richey-Yowell, Angela R. G. Santos, Rafael A. Garcia, Desmond H. Grossmann, Zachary R. Claytor, Paul G. Beck

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

Nonlinear Causality and Strong Hyperbolicity of Einstein-Israel-Stewart Theories of Transient Relativistic Fluid Dynamics

Ian Cordeiro, Enrico Speranza, Fábio S. Bemfica et al. (+2 more)

We present the first complete analysis of nonlinear causality and local well-posedness for a very general class of bulk and shear viscous theories of relativistic transient fluid dynamics, which encompasses (i) the original Israel-Stewart theory derived from entropy-current arguments, (ii) approaches derived from kinetic theory, and (iii) resummed gradient-expansion based formulations as particular subcases. Our work establishes, for the first time, simultaneously necessary and sufficient algebraic conditions for causality, alongside sufficient conditions guaranteeing strong hyperbolicity, in the full nonlinear regime. These results are rigorously proven for both systems coupled to Einstein's equations featuring a dynamic metric and on a fixed background, with or without a cosmological constant, and include baryon conservation (in the absence of heat/diffusion currents). The conditions are purely algebraic, require no simplifying spacetime symmetry assumptions or a specific equation of state, and allow all transport coefficients to depend on the dissipative currents. We also demonstrate that the normalization, orthogonality, symmetry, and tracelessness physical constraints on the dynamical variables are properly propagated during the lifetime of the solutions. Our results provide a readily usable toolset with which one can investigate the domain of applicability of relativistic viscous fluid dynamics in numerical and phenomenological studies in heavy-ion collisions and astrophysics.
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All authors Ian Cordeiro, Enrico Speranza, Fábio S. Bemfica, Marcelo M. Disconzi, Jorge Noronha

Instrumentation and Methods for Astrophysics

Detection of Organics in Water Ice by Optical-PhotoThermal Infrared Spectroscopy

Christopher S. Duffey, Julie Brisset, Myles Hoskinson et al. (+2 more)

The detection and characterization of organic molecules within water ice is vital for interpreting observations of icy moons and comets. However, organic-ice interactions often distort intrinsic water-ice absorption features, complicating infrared (IR) spectral analysis. This study evaluated Optical Photothermal Infrared (O-PTIR) spectroscopy as a non-destructive, sub-micrometer resolution technique to detect and quantify embedded organics. Using a temperature-controlled sample environment to maintain ice stability, frozen mixtures of amino and hydroxy acids were analyzed across a broad concentration range. L-glycine was successfully detected down to approximately $10^{-6}\text{ M}$, yielding an experimental limit of detection (LOD) of $0.2\,\mu\text{M}$ and a limit of quantification (LOQ) of $3.83\,\mu\text{M}$. Furthermore, O-PTIR measurements of binary mixtures containing L-glycine and lactic acid demonstrated the capacity to differentiate and quantify multiple organic components within a single ice matrix. Notably, a broad absorption feature centered near the water-bending mode appeared exclusively in organic-bearing ice samples and was absent in pure $\text{H}_2\text{O}$ and $\text{D}_2\text{O}$ controls. Comparative analysis in these matrices revealed that embedded organics actively perturb intrinsic ice features, providing new constraints on organic-ice interactions. Ultimately, these results demonstrate that O-PTIR spectroscopy can reliably detect, quantify, and spatially resolve organic compounds in water ice while preserving crucial sample context. The technique offers a promising framework for future laboratory investigations of icy planetary materials and directly informs the interpretation of spectroscopic data from volatile-rich space environments.
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All authors Christopher S. Duffey, Julie Brisset, Myles Hoskinson, Jakob Haynes, Kathrine Lyakh

High Energy Astrophysical Phenomena

Analyzing Cosmic Ray Spectral Features: A Numerical Investigation

Yuca C. Chen, Zachary M. Dorris, Eun-Suk Seo et al. (+1 more)

Recent cosmic ray space-based and balloon-borne experiments have revealed various spectral features. Spectral hardening around ~200 GV has been seen in primary nuclei as well as secondaries produced during propagation. Proton spectrum softening at ~10 TV and helium spectrum softening at a few tens TV has also been seen. Additionally, a positron excess has been observed above ~25 GeV. The cosmic ray propagation code, GALPROP v57, was utilized to investigate the cause behind these features. A diffusion model with reacceleration and convection effects was used as a baseline. To find the best fit to the experimental data, GALPROP v57's parameter optimization module, utilizing the external numerical minimization software MINUIT2, was used. For the hardening, three scenarios were studied: (1) a diffusion coefficient break, (2) injection spectra breaks, and (3) a combination of both breaks. An additional injection spectrum break was considered to fit the softening of the proton and helium spectra. An additional positron source was introduced for the positron excess. The resulting elemental spectra and ratios, along with the all-particle spectrum, are compared to compiled cosmic ray data. Implications of these spectral features are also discussed.
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All authors Yuca C. Chen, Zachary M. Dorris, Eun-Suk Seo, Vladimir S. Ptuskin

Instrumentation and Methods for Astrophysics

The Wide-field Spectroscopic Telescope: optical designs for the low-resolution multi-object spectrographs

Will Saunders, Kjetil Dohlen, Dimitri Buffat et al. (+7 more)

In MOS Low-Resolution mode, WST has a 'spectral etendue' per fiber (etendue x spectral resolution elements) twice as large as any existing MOS instrument, and a total spectral etendue ~20 times larger. Combined, these present enormous challenges for the spectrograph design. Initial designs were based on (a) a novel F/0.775 Folded Solid Schmidt camera with 6cm detectors, (b) an F/1.15 dioptric camera with 6cm detectors, and (c) an F/1.31 dioptric camera with 9cm detectors, all with YAG field-flatteners. However, the imperative of fast camera speed has greatly diminished, as the projected cost and read-noise of large format CMOS detectors is projected to decrease greatly. The adopted baseline solution has 4 dioptric F/1.64 cameras, each with two doublets, a YAG field lens and 9cm x 9cm detector. Theoretical image quality is 8 microns rms radius. The design seems readily athermalised, potentially allowing passive temperature control. Each spectrograph accepts 500+ fibers. Expected RoM costs (scaled from earlier designs) suggest a total cost <4M Euro per spectrograph.
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All authors Will Saunders, Kjetil Dohlen, Dimitri Buffat, Roelof S. de Jong, Olaf Iwert, David Lee, Lawrence Bissel Andrea Bianco, Ross Zhelem, Etienne Burtin, Virgile Meyer

Earth and Planetary Astrophysics

Tracing the source of carbon oxides on the large moons of Uranus

Richard J. Cartwright, Sasha Cryan, Rosario Brunetto et al. (+15 more)

The Uranian moons Ariel, Umbriel, Titania, and Oberon are enriched in CO2 mixed with CO, but the origin(s) of these carbon oxides, be they primarily native or radiolytic, remains uncertain. Using data collected by NIRSpec on the James Webb Space Telescope (JWST), we measured the spectral signature of CO2 and other carbon oxides to help disentangle these hypotheses. Through comparison to laboratory data, we find that many of the detected spectral features are consistent with CO2 ice, including 12CO2 scattering peaks (4.15 - 4.26 microns), multi-lobe 13CO2 bands (4.35 - 4.43 microns), and CO2 biphonon and triphonon modes (4.80 - 5.25 microns). Our measurements show that CO2 and CO are concentrated on the trailing hemispheres of the inner moons Ariel and Umbriel, potentially supporting a radiolytic production hypothesis, consistent with prior ground-based results. However, many of the identified spectral features are only observed in thick crystalline ice deposits measured in the laboratory, which may be difficult to form via radiolysis of carbon-bearing material mixed in icy regoliths. Similarly, the data exhibit weak 4.02 microns and 4.40 microns bands, hinting at the presence of carbonate minerals and 13CO2 clathrates, respectively, possibly formed in the interiors of these moons. Furthermore, JWST has revealed that CO2 is widespread at Uranus, present in its system of rings, ring moons, and irregular satellites, consistent with its largest moons accreting CO2 and other carbon oxides from the Uranian subnebula. We conclude that exposed carbon oxides are potentially native, with their surface distributions shaped by charged particle irradiation and seasonal sublimation-condensation cycles.
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All authors Richard J. Cartwright, Sasha Cryan, Rosario Brunetto, Apolline Leclef, Eric Quirico, Bryan J. Holler, William M. Grundy, Tom A. Nordheim, Ujjwal Raut, Matthew M. Hedman, Riley A. DeColibus, Chloe B. Beddingfield, Marc Neveu, Christopher R. Glein, Sara Faggi, Geronimo L. Villanueva, Noemi Pinilla-Alonso, Stephanie M. Menten