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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 23 March

High Energy Astrophysical Phenomena

The full evolution of the type-C QPO in MAXI J1348-630 revealed by Insight-HXMT

X.-L. Wang, Z. Yan, F.-G. Xie et al. (+4 more)

Based on abundant data from Insight-HXMT, we conducted a detailed analysis of type-C quasi-periodic oscillations (QPOs) in the black hole X-ray binary MAXI J1348-630. Type-C QPOs were intensively detected over a broad energy band, with frequencies ranging from 0.24 to 10.3 Hz, and several new evolutionary features were identified. First, although type-C QPOs reappear intermittently, they show a stable characteristic frequency around 7 Hz. This implies a characteristic spatial scale for the QPO emission region, despite large variations in outburst intensity. Second, from the hard state to the hard-intermediate state, type-C QPOs display a harder fractional rms spectrum, with the rms peak shifting toward high energies (>20 keV) and an amplitude exceeding 10 %. This hard rms spectrum favors a high-energy origin for type-C QPOs. The spectral hardening occurs simultaneously with the weakening of the compact jet, suggesting a physical connection between these two processes. Finally, we observed hysteresis in the QPO frequency-flux relation, with the hysteresis loop evolving in opposite directions between the main and mini-outbursts. This offers a new perspective on the physical differences between the two outburst types, which may arise from variations in initial magnetic field conditions.
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All authors X.-L. Wang, Z. Yan, F.-G. Xie, J.-F. Wang, Y.-X. Li, Z.-Y. Liu, R.-Y. Ma

Solar and Stellar Astrophysics

Solar Radio Bursts in the metric to kilometric range

Anshu Kumari, Mugundhan V., Diana E. Morosan et al. (+6 more)

Solar radio bursts (SRBs) are intense emissions observed in radio wavelengths most frequently during solar transients, such as coronal mass ejections (CMEs) and flares. SRBs are direct signatures of accelerated electrons in the solar atmosphere. These solar transients have a direct impact on the near-Earth atmosphere. SRBs serve as key diagnostic tools for plasma processes, particle accelerations, magnetic field dynamics in the solar corona and the heliosphere, which are the root cause of these solar transients. There are several key science question which solar radio observations can answer, such as: When $\&$ where is the bulk of the energy released in flares?, what are the physical properties of the energy release site?, what are the properties of heated plasma $\&$ accelerated particles?, how does the transport of heated plasma $\&$ accelerated particles?, what bearing do flares have on the question of coronal heating? The Square Kilometre Array (SKA), with its unprecedented sensitivity, temporal, spectral, and spatial resolution, as well as dynamic range, is expected to provide an enhanced understanding of the physics behind solar transients with unprecedented detail.
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All authors Anshu Kumari, Mugundhan V., Diana E. Morosan, Jasmina Magdalenic, Ketaki Deshpande, Peijin Zhang, Divya Paliwal, Pietro Zucca, Puja Majee

Earth and Planetary Astrophysics

Direct spectroscopic confirmation of the young embedded proto-planet WISPIT 2c

Chloe Lawlor, Richelle F. van Capelleveen, Guillaume Bourdarot et al. (+18 more)

WISPIT 2 is a nearby young star with a multi-ringed disk which was recently confirmed to host a ~4.9 MJup gas giant planet embedded in a large (60 au) gap at a radial separation of 57 au from the host star. We confirm and characterise a second, close-in planet in the WISPIT 2 system using a combination of new VLT/SPHERE H-band dual-polarisation imaging and VLTI/GRAVITY K-band interferometric observations of the WISPIT 2 system. The GRAVITY detection is consistent with a point-like source while its extracted K-band spectrum shows CO band-head absorption at 2.3 microns and a continuum shape consistent with a young giant planet. From the GRAVITY data we extract a medium resolution K-band spectrum of the companion and fit atmospheric model grids using the species tool with nested sampling to constrain its effective temperature, radius, and luminosity. We infer Teff of 1500-2600 K, a radius of 0.91-2.2 RJup, and a luminosity of (-3.47)-(-3.63). Comparison with evolutionary tracks implies a mass range of 8-12 MJup, approximately twice as massive as the previously confirmed WISPIT 2b. The astrometry rules out a background source and marginally detects orbital motion of WISPIT 2c, which needs further follow-up observations for confirmation. WISPIT 2 now becomes an analogue to PDS 70, offering a second laboratory for studying the formation and early evolution of a multi-planet system within its natal disk.
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All authors Chloe Lawlor, Richelle F. van Capelleveen, Guillaume Bourdarot, Christian Ginski, Matthew A. Kenworthy, Tomas Stolker, Laird Close, Alexander J. Bohn, Frank Eisenhauer, Paulo Garcia, Sebastian F. Hönig, Jens Kammerer, Laura Kreidberg, Sylvestre Lacour, Jean-Baptiste Le Bouquin, Eric Mamajek, Mathias Nowak, Thibaut Paumard, Christian Straubmeier, Nienke van der Marel, the exoGRAVITY Collaboration

Earth and Planetary Astrophysics

Lava Lakes on Io: crust age and implications for thermal output

Alessandro Mura, Rosaly M. C. Lopes, Federico Tosi et al. (+12 more)

Recent observations by the JIRAM instrument onboard NASA's Juno mission have confirmed that many of Io's volcanic hot spots are active lava lakes, characterized by a colder central crust surrounded by a hotter peripheral ring. In this study, we investigate the thermal properties of thirty such lava lakes, providing new constraints on their structure and energy budget. We find that most of the total power from Io's lava lakes comes from their low-temperature crusts rather than the hotter peripheral rings, suggesting previous estimates underestimated lava lake power by up to a factor of 10. Io's paterae undergo stochastic resurfacing on timescales of roughly a decade, with each lake possibly following its own characteristic cycle. We also explore the relationship between the average temperature of the crust and the evolutionary state of each lake, offering insights into the frequency of resurfacing processes. Finally, we propose an improved assessment of Io's global thermal output, emphasizing that only full-surface observation of Io with sufficient spatial and spectral resolution can yield realistic values for the moon's volcanic total heat flux.
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All authors Alessandro Mura, Rosaly M. C. Lopes, Federico Tosi, Peter J. Mouginis-Mark, Jani Radebaugh, Francesca Zambon, Matteo Paris, Scott Bolton, Alberto Adriani, Roberto Sordini, Andrea Cicchetti, Raffaella Noschese, Giuseppe Piccioni, Christina Plainaki, Giuseppe Sindoni

High Energy Astrophysical Phenomena

Millihertz quasi-periodic oscillations in accreting X-ray pulsars

Wen Yang and Wei Wang

Accreting neutron stars exhibit pulsed X-rays and complex temporal variability across multi-wavelengths and different timescales. This variability could be driven by various physical processes including instability or inhomogeneous motions within the accretion flow, thermonuclear bursts on the neutron star surface. In this review, we present a concise overview of the observational features for millihertz (mHz) quasi-periodic oscillations (QPOs) at a frequency range of $\sim 1- 1000$ mHz observed in light curves of X-ray pulsars for both low-mass X-ray binaries and high-mass X-ray binaries, based on recent X-ray missions, e.g., NICER, Insight-HXMT and NuSTAR. We further summarize current theoretical interpretations, discuss remaining challenges and propose potential directions for future studies to advance the understanding of the nature and physical origin of these QPOs.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Kinky vortons in the 2HDM

Richard A. Battye, Steven J. Cotterill and Adam K. Thomasson

We construct and analyse two-dimensional, current-carrying ring solutions, known as kinky vortons, in the $\mathbb{Z}_2$-symmetric global two-Higgs-doublet model (2HDM). We demonstrate the existence of multiple dynamically stable configurations that persist under non-axially symmetric perturbations. These solutions are described with high accuracy by the thin string approximation and elastic string formalism, which correctly capture both their equilibrium radii and dynamical oscillation frequencies. Kinky vortons in the $\mathbb{Z}_2$-symmetric theory establish the viability of vorton solutions in a phenomenologically motivated extension of the Standard Model, and should provide a computationally tractable proxy for vortons in the $U(1)$-symmetric 2HDM. In addition, we identify a composite domain wall configuration in which localized condensates are supported on secondary domain walls existing on a $\mathbb{Z}_2$ wall, suggesting a mechanism by which kinky-vorton-like defects could arise in a three dimensional setting.
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Solar and Stellar Astrophysics

Formation of black holes from He stars

Gang Long, Bo Wang, Philipp Podsiadlowski et al. (+5 more)

Massive He stars are potential candidates of type Ib/c supernova (SN) progenitors. Understanding their final fates remains a key issue in astrophysics. In this work, we investigate the evolution of He stars with initial masses from 5 $M_\odot$ to 65 $M_\odot$, focusing on the presupernova (pre-SN) core structures to assess their explodability. Our simulations indicate that the final core structure is determined by the CO core mass and the central 12C mass fraction at the end of core He burning, affecting the properties of central C-burning and the locations of convective shells. The location of the last convective C-burning shell sets the mass of the C-free core, constraining the iron core mass and compactness. We found that the final compactness and iron core mass exhibit non-monotonic behavior with initial mass, suggesting that the boundary between neutron star and black hole formation is not a simple mass threshold. This is due to core C/Ne burning becoming neutrino dominated. This process drives stronger core contraction, ultimately increasing the iron core mass and the final compactness. In contrast, earlier core Ne/O/Si ignition and shell mergers inhibit core contraction, reducing both the iron core mass and final compactness. We also discuss the effects of metallicity and overshooting on the pre-SN core structure. These factors potentially affect the explodability of progenitors.
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All authors Gang Long, Bo Wang, Philipp Podsiadlowski, Dongdong Liu, Yunlang Guo, Shuai Zha, Hanfeng Song, Zhanwen Han

Astrophysics of Galaxies

JOYS: Linking the molecular ice and gas-phase composition towards the high-mass hot core IRAS 18089-1732

C. Gieser, W. R. M. Rocha, Y. Chen et al. (+11 more)

Context. The formation and destruction of molecules in the interstellar medium is a complex interplay between gas-phase reactions as well as processes on grain surfaces and within icy mantles. For many decades, the gas-phase composition of the cold material towards star-forming regions could be well characterized using (sub)mm facilities. Prior to the launch of the James Webb Space Telescope (JWST), ice species other than the main constituents (H2O, CO, CO2, NH3, CH4, CH3OH) were challenging to detect due to insufficient sensitivity as well as angular and/or spectral resolution. Aims. We determine molecular ice and gas-phase column densities towards the young and embedded high-mass hot core IRAS 18089-1732 within a region of 5000 au. Methods. We use spectroscopic data from 5-28 micron obtained with JWST to derive ice column densities of H2O, SO2, OCN-, CH4, HCOO-, HCOOH, CH3CHO, CH3COOH, C2H5OH, CH3OCH3, and CH3COCH3. Gas-phase column densities of a total of 38 molecules, including, O-, N-, S-, and Si-bearing species as well as less abundant isotopologues, are inferred from sensitive molecular line observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA) at 3 mm wavelengths. Results. We find comparable abundances (relative to C2H5OH or CH3OH) in both phases for C2H5OH, CH3OH, and CH3OCH3. The abundances of SO2 and CH3COCH3 are higher in the gas-phase suggesting additional gas-phase formation routes. The abundance of CH3CHO is one order of magnitude higher in the ices compared to the gas-phase. The ice abundances (relative to H2O ice) towards the IRAS 18089 hot core are similar to previously studied Galactic low- and high-mass protostars. There are hints of a decreasing abundance with Galactocentric distance for OCN-, CH3OH, and CH3CHO ice. (abridged)
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All authors C. Gieser, W. R. M. Rocha, Y. Chen, K. Slavicinska, E. F. van Dishoeck, P. Nazari, N. G. C. Brunken, L. Francis, H. Beuther, S. Reyes-Reyes, A. Caratti o Garatti, P. D. Klaassen, J. M. Vorster, M. G. Navarro

Cosmology and Nongalactic Astrophysics

A plug-and-play approach with fast uncertainty quantification for weak lensing mass mapping

Hubert Leterme, Andreas Tersenov, Jalal Fadili et al. (+1 more)

Upcoming stage-IV surveys such as Euclid and Rubin will deliver vast amounts of high-precision data, opening new opportunities to constrain cosmological models with unprecedented accuracy. A key step in this process is the reconstruction of the dark matter distribution from noisy weak-lensing shear measurements. Current deep-learning-based mass-mapping methods achieve high reconstruction accuracy, but either require retraining a model for each new observed sky region (limiting practicality) or rely on slow Markov chain Monte Carlo sampling. Efficient exploitation of future survey data therefore calls for a new method that is accurate, flexible, and fast at inference. In addition, an uncertainty quantification with coverage guarantees is essential for a reliable cosmological parameter estimation. We introduce PnPMass, a plug-and-play approach for weak-lensing mass mapping. The algorithm produces point estimates by alternating between a gradient descent step with a carefully chosen data fidelity term and a denoising step implemented with a single deep-learning model trained on simulated data corrupted by Gaussian white noise. We also propose a fast sampling-free uncertainty quantification scheme based on moment networks, with calibrated error bars obtained through conformal prediction to ensure coverage guarantees. Finally, we benchmark PnPMass against model-driven and data-driven mass-mapping techniques. PnPMass achieves a performance close to that of the currently best deep-learning methods while offering fast inference. It converges in just a few iterations, and it requires only a single training phase, regardless of the noise covariance of the observations. It therefore combines flexibility, efficiency, and reconstruction accuracy while delivering tighter error bars than existing approaches, making it well suited for upcoming weak-lensing surveys.
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All authors Hubert Leterme, Andreas Tersenov, Jalal Fadili, Jean-Luc Starck

Astrophysics of Galaxies

Observations of Early Black Holes Before and After JWST

Eduardo Banados

These notes are from three lectures given at the 54th Saas-Fee Advanced Course of the Swiss Society of Astrophysics and Astronomy in January 2025. This chapter reviews the dramatic evolution in our understanding of supermassive black holes in the first billion years, from ground-based discoveries to recent space-based infrared observations with JWST. Section 1 introduces AGN and quasars to contextualise observations at the highest redshifts. Section 2 reviews the pre-JWST understanding of early quasars, including personal accounts of how key discoveries were made. Section 3 examines how JWST is transforming the field, from black hole mass measurements and host galaxy characterisation to large-scale environmental studies, and identifies emerging directions.
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High Energy Astrophysical Phenomena

H.E.S.S. observations of composite Seyfert-starburst galaxies

H.E.S.S. Collaboration, A. Acharyya, F. Aharonian et al. (+120 more)

Context: Composite galaxies that contain both Seyfert and starburst components may produce very high-energy (VHE; >100 GeV) gamma-ray emission at a wide range of spatial scales, from a few Schwarzschild radii of a supermassive black hole to dimensions of kiloparsec-size jet-driven outflows. In addition to supernova remnants, various sources have been suggested to explain data collected on composite galaxies, including multi-messenger neutrino and ultra-high-energy cosmic-ray data. Aims: The closest composite Seyfert-starburst galaxies (NGC 1068, the Circinus galaxy, and NGC 4945) are observed with the High Energy Stereoscopic System (H.E.S.S.) to provide constraints on cosmic-ray populations in these systems. Methods: Data obtained in H.E.S.S. observations have been analyzed to search for VHE gamma-ray counterparts to the GeV gamma-ray signals detected with Fermi-LAT and for potential spectral components in the VHE range. Results: No significant signals have been found in these H.E.S.S. data. Upper limits on the VHE gamma-ray fluxes were applied to constrain theoretical models involving different spectral components.
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All authors H.E.S.S. Collaboration, A. Acharyya, F. Aharonian, H. Ashkar, M. Backes, V. Barbosa Martins, R. Batzofin, Y. Becherini, D. Berge, M. Böttcher, C. Boisson, J. Bolmont, J. Borowska, F. Brun, B. Bruno, C. Burger-Scheidlin, S. Casanova, J. Celic, M. Cerruti, S. Chandra, A. Chen, M. Chernyakova, J. O. Chibueze, O. Chibueze, S. Colafrancesco, T. Collins, B. Cornejo, G. Cotter, J. Damascene Mbarubucyeye, J. de Assis Scarpin, M. de Bony de Lavergne, M. de Naurois, E. de Oña Wilhelmi, A. G. Delgado Giler, A. Djannati-Ataï, J. Djuvsland, A. Dmytriiev, R. Ebrahim, K. Egg, C. Escañuela Nieves, K. Feijen, M. D. Filipovic, G. Fontaine, S. Funk, S. Gabici, J.F. Glicenstein, J. Glombitza, P. Goswami, M.-H. Grondin, B. Hess, J.A. Hinton, T. L. Holch, M. Holler, D. Horns, M. Jamrozy, F. Jankowsky, I. Jung-Richardt, E. Kasai, K. Kasprzak, K. Katarzyński, D. Kerszberg, B. Khélifi, N. Komin, K. Kosack, D. Kostunin, R.G. Lang, S. Lazarević, V. Lefranc, J.-P. Lenain, P. Liniewicz, A. Luashvili, J. Mackey, D. Malyshev, D. Malyshev, V. Marandon, P. Marchegiani, M. Mayer, A. Mehta, A.M.W. Mitchell, R. Moderski, M.O. Moghadam, L. Mohrmann, E. Moulin, J. Niemiec, P. O'Brien, L. Olivera-Nieto, S. Panny, M. Panter, R.D. Parsons, U. Pensec, D. A. Prokhorov, G. Pühlhofer, M. Punch, A. Quirrenbach, M. Regeard, A. Reimer, O. Reimer, H. Ren, F. Rieger, B. Rudak, K. Sabri, V. Sahakian, H. Salzmann, M. Sasaki, F. Schüssler, J.N.S. Shapopi, W. Si Said, S. Spencer, Ł. Stawarz, S. Steinmassl, T. Tanaka, A.M. Taylor, R. Terrier, M. Tsirou, T. Unbehaun, C. van Eldik, M. Vecchi, C. Venter, J. Vink, T. Wach, A. Wierzcholska, A. Zech, W. Zhong

Earth and Planetary Astrophysics

Planetary Architectures of Kepler Compact Multis with Binary Star Companions

Kendall Sullivan and Gregory J. Gilbert

Planets in binary-star systems exhibit demographic differences compared to planets in single-star systems. In particular, planets with binary-star hosts have a lower overall occurrence rate compared to their single-star counterparts, as well as a suppressed relative occurrence rate for sub-Neptunes ($R_p=2{-}4R_{\oplus}$) compared to super-Earths ($R_p=1.0{-}1.5R_{\oplus}$). These differences are most pronounced in close separation binaries ($\rho < 100$ au) which has been interpreted as a result of binary stars disrupting the protoplanetary disks of their stellar companions. The architectures of planetary systems – i.e. the arrangements of planet sizes and orbits – provide additional information about system formation and evolution. Architectures of single-star planetary systems are well studied, but architectures of binary-star planetary systems have not been investigated in detail. In this work, we analyzed a large sample of Kepler planetary systems (162 planets in 118 binary-star systems; 880 planets in 544 single-star systems) to compare their architectures as a function of stellar multiplicity. We found that planets with binary-star hosts follow a similar “peas-in-a-pod” tendency toward uniformity in planet radii and log-uniformity in period spacing as planets with single-star hosts. However, we also detected modest ($2.5-3\sigma$) differences in period spacing and planet multiplicity, with binary-star systems having higher typical gap complexities (indicating more uneven spacing) and a higher prevalence of single planets. We interpret these results as evidence that binary stars primarily influence the planetary architectures of their stellar companions by shaping the protoplanetary disk at formation, with subsequent dynamical processing more gently altering the system architectures over secular timescales.
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Solar and Stellar Astrophysics

On the Constraints and Observational Manifestations of Failed Solar Eruptions in Toroidal Magnetic Cage

Jinhan Guo, Y. Guo, H. Wu et al. (+9 more)

Observations show that many solar eruptions remain confined within strong overlying magnetic fields, forming a so-called magnetic cage. While confinement by poloidal overlying fields has been widely investigated, the role of strong external toroidal fields remains unclear. Using three-dimensional magnetohydrodynamic simulations, we study confined eruptions in a toroidal magnetic cage, focusing on the interplay between the Lorentz force and magnetic reconnection, and their observational signatures. We further employ a guiding-center test-particle approach to synthesize hard X-ray emission for comparison between thermal and nonthermal responses. We find that overlying toroidal fields play a crucial role in confinement by generating strong return currents that produce a significant downward Lorentz force, suppressing flux rope ascent. At the same time, they induce large-angle rotation of the flux rope, leading to reconnection with overlying fields and eventual break-up. Synthetic EUV emission reveals multi-ribbon flares with highly sheared, globally cowboy-hat-like loop structures. Hard X-ray diagnostics show that thermal and nonthermal emissions are not co-spatial, with return currents acting as an efficient accelerator of energetic electrons. These results demonstrate that toroidal-field-induced forces govern both the confinement and rotation of erupting flux ropes, providing an explanation for failed eruptions even under torus-unstable conditions. These results suggest that the morphology and shearing angle of flare loops are the useful diagnostics for distinguishing confined from eruptive events.
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All authors Jinhan Guo, Y. Guo, H. Wu, B. Schmieder, P. Démoulin, Y. W. Ni, C. Wang, S. Poedts, T. Li, Wensi Wang, Y. H. Zhou, P. F. Chen

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

Observational Constraints on Noncoincident $f(Q)$-Gravity with Matter-Gravity Coupling

Andronikos Paliathanasis

We investigate $f\left( Q\right) $-gravity with a matter-gravity coupling as a geometric dark energy candidate for the description of the late-time cosmic acceleration within a spatially flat Friedmann–Lemaître-Robertson-Walker geometry. We select a noncoincident connection that naturally follows from the general framework of cosmological models with nonzero spatial curvature. We present observational constraints for the simplest $f\left( Q\right) =f_{0}Q^{n}$ model using data from Supernovae, Baryon Acoustic Oscillations and Cosmic Chronometers. For different data combinations we found consistent constraints, with a best-fit value for the power-law index $n\simeq2$. A comparison with the $\Lambda$CDM model shows that the $f\left( Q\right) $-gravity leads to larger values for the likelihood, while Akaike's Information Criterion suggests statistical equivalence between the two models for most data combinations.
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Earth and Planetary Astrophysics

New surface composition and temperature maps of Pluto from New Horizons LEISA data

A. E. Drozdov and N. V. Emelyanov

New Horizons RALPH/LEISA near-infrared spectra allow for regional mapping of Pluto's surface ices and their physical state; however, scan-to-scan artifacts and variable spatial resolution complicate quantitative interpretation. We extend previous LEISA compositional studies (Protopapa et al., 2017(arXiv:2110.00662); Schmitt et al., 2016; Emran et al., 2023(arXiv:2301.06027)) by combining five close-approach observations into co-registered equirectangular maps at 7 km/pixel and by jointly retrieving surface temperature, ice abundances, and grain sizes using a Hapke-based mixing model. We mitigate bad pixels and edge overexposure linked to flat-field uncertainties and correct for residual scan-to-scan spectral discrepancies using per-observation scale and offset terms. The resulting maps provide distributions of CH4-rich ice, N2-rich ice, H2O ice, and Titan tholins, alongside a corresponding temperature map.
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Instrumentation and Methods for Astrophysics

Diffuse and specular brightness models applied to LEO satellites. Case study: The ONEWEB constellation

María Romero-Colmenares, Katherine Vieira, Jeremy Tregloan-Reed et al. (+11 more)

Context. To better understand the observed brightness of low Earth orbit satellites, we must characterize their reflectivity, which in turn depends importantly on their bus designs. The reflectivity of a body can be described by Lambert's law, in terms of its albedo, cross-sectional area, range (distance), phase angles, and the mixing coefficient between diffuse and specular reflection components. Aims. We aim to analyze the reflectivity of more than 300 ONEWEB satellites using the diffuse Lambertian sphere, diffuse and specular Lambertian sphere, and the relative reflectance brightness models. Methods. Astrometric and photometric measurements, plus two-line elements (TLE) orbital information were used to compute the apparent and range-magnitude, as well as the relevant angles related to the orientation of the Sun, the satellites, and the observer. A differential evolution Monte Carlo algorithm was used to obtain each model's parameters that best fit the data. Results. All models can fit the mean observed brightness of the satellites but cannot describe the observed phase-angle-dependent brightness modulations. The residuals in all cases have a standard deviation of $\sim$0.6 magnitudes, while the observational photometric errors are on average $\sim$0.2 magnitudes. Conclusions. The studied brightness models, which depend on the relative Sun-body-observer position but are independent of the specific orientation of the reflecting body surface(s) with respect to the observer, cannot entirely explain the observed brightness of the ONEWEB constellation satellites. Accounting for the real shape and the changing attitude of the satellite, as well as the effect of Earth's albedo is needed to better explain satellite photometric observations
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All authors María Romero-Colmenares, Katherine Vieira, Jeremy Tregloan-Reed, Yonggi Kim, Joh-Na Yoon, Ha-eun Kim, Hyo-ri Jeon, Chae-rin Kim, Christian Adam, Tobías C. Hinse, Mario Soto, Eduardo Unda-Sanzana, Penélope Longa-Peña, Ángel Otarola

Astrophysics of Galaxies

The MUSE Ultra Deep Field (MUDF) VIII. The cool gas distribution surrounding galaxies at redshifts z ~ 0.5-2

Edoardo Santo, Michele Fumagalli, Seok-Jun Chang et al. (+5 more)

We use deep MUSE data from the MUDF survey to investigate the cool gas around galaxies at redshifts 0.5 < z < 2. We constructed two samples: one sample for a down-the-barrel analysis, probing outflows via MgII absorption against galaxy continua, and the other sample for projected galaxy pairs to examine the gas around the foreground galaxies in the transverse direction. From down-the-barrel stacked spectra, we detected blueshifted MgII absorption, indicative of outflows, in which the absorption strength increases with stellar mass and star formation rate. Lower-mass galaxies exhibit weaker absorption, but higher outflow velocities, whereas higher-mass systems retain more cool gas with slower outflows. In the transverse direction, the absorption of MgII decreases with the impact parameter, following a shallow profile. Comparing observations with radiative transfer models, we found that extrapolating an expanding halo model constrained with down-the-barrel measurements to halo scales overestimates the observed equivalent widths, likely due to the outflow geometry and the absence of the interstellar medium in the model. Our results highlight that mass, outflow geometry, and gas retention shape the cool circumgalactic medium, and that the combination of absorption and emission diagnostics provides powerful constraints on the properties of the cold halo gas.
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All authors Edoardo Santo, Michele Fumagalli, Seok-Jun Chang, Max Gronke, Rajeshwari Dutta, Matteo Fossati, Mitchell Revalski, Marc Rafelski

High Energy Astrophysical Phenomena

The pulsar population of Omega Centauri: New TRAPUM searches, timing, and cluster dynamics with MeerKAT and Parkes

Miquel Colom i Bernadich, Shi Dai, Federico Abbate et al. (+28 more)

Millisecond pulsars (MSPs) are probes of globular clusters, tracing their stellar evolution, cluster dynamics, and gravitational potential. We searched for and timed MSPs in the Omega Centauri, then investigated their high-energy emission, the cluster potential, and MSP demographics. We performed Fourier-domain acceleration and jerk searches on MeerKAT observations, followed by pulsar timing using MeerKAT and Parkes Murriyang data spanning 2021-2025. We discovered the new isolated MSP PSR J1326-4728S (PSR S, Ps=4.538 ms and DM=96.24 pc/cm3. We updated the timing solutions for PSRs A-E, obtained the first timing solutions for G, H, and K, and updated the orbital parameters for I, L, N, and Q. The latter three, I, N, and Q, have significantly longer orbital periods (Pb=1-7 days) than previously reported. Pulsars B, G, H, K, and L are black widows (Pb=2-4 hours); I is a wide-orbit (Pb=3.50 days) MSP with a light ~0.05 Mo companion; N and Q have ~0.25 Mo companions; and N shows a significant orbital eccentricity (e=0.093). We folded Fermi-LAT and NICER photons to search for high-energy pulsations, but failed to detect them from individual MSPs. Significant spin period derivatives were measured for eight MSPs and interpreted as arising from the cluster gravitational potential. The inferred line-of-sight accelerations are consistent with a King-model gravitational potential, and allow us to set an upper central black hole mass limit of Mbh<8e4 Mo at 90% confidence. The high fraction of isolated MSPs (58%) and black widow systems (63% of binaries), and possibly the eccentricity of N, are difficult to reconcile with MSP population predictions based solely on encounter rates. Instead, these properties require alternative formation channels or reflect the complex evolutionary history of Omega Centauri, with part of its MSP population having formed in denser environments than those observed today.
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All authors Miquel Colom i Bernadich, Shi Dai, Federico Abbate, Matthew Kerr, Matteo Bachetti, Yash Bhargava, Sarah Buchner, Simon Johnston, Marta Burgay, Andrea Possenti, Rouhin Nag, Alessandro Ridolfi, Amodio Carleo, Alessandro Corongiu, Paulo C. C. Freire, Fernando Camilo, Weiwei Chen, Mario Cadelano, Dhanraj Risbud, Prajwal V. Padmanabh, David J. Champion, Michael Kramer, Benjamin Stappers, Maciej Serylak, Vishnu Balakrishnan, Matthew Bailes, Arunima Dutta, Laila Vleeschower Calas, Vivek Venkatraman Krishnan, Yunpeng Men, Ewan Barr

Astrophysics of Galaxies

APOSTLE vs. AURIGA Simulations: How Subgrid Models Shape Milky Way Analogs

Jianhong Hu, Hang Yang and Liang Gao

Despite significant progress in cosmological simulations of galaxy formation, the role of subgrid physics in shaping the detailed properties of galaxies remains incompletely understood. In this work, we analyze two sets of zoom-in simulations that share identical initial conditions but adopt distinct implementations of baryonic physics, enabling a controlled comparison of their predictions. We examine the stellar properties, morphological structures, and satellite populations of the simulated galaxies at $z=0$. We find that AURIGA galaxies systematically exhibit higher stellar masses and surface densities than their APOSTLE counterparts. These differences are primarily driven by variations in the efficiency of gas cooling from the circumgalactic medium (CGM) into the star-forming gas. Both simulations form well-defined disk galaxies; however, AURIGA systems generally display higher disk-to-total mass ratios, earlier disk formation, and more prominent dynamical structures such as bars and spiral arms. Nevertheless, strongly disk-dominated systems are present in both simulations, although they do not arise in the same host haloes. The vertical disk structure in both simulations is well described by a sech density profile, with scale heights below ~ 1 kpc in the inner regions. The satellite populations also differ, with AURIGA producing systematically more massive satellites, including a ~ 0.3 dex increase in the most massive system, while the number of satellites above $10^6 M_{\odot}$ remains comparable in most halo pairs. Both simulations reproduce similar satellite stellar mass–metallicity relations, albeit ~ 0.25 dex higher than observation. This comparative study therefore provides useful benchmarks for future efforts to better constrain galaxy formation models.
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Solar and Stellar Astrophysics

Fine-tuning of light-time effect in triple systems

David Vokrouhlický

The sequence of eclipses of binary stars is subject to inequalities for various reasons. The presence of a third component in the system causes periodic motion of the binary's center of mass along the line of sight of an observer. The finite value of the light velocity implies that the epochs of eclipses periodically advance and delay with respect to the exact orbital period of the binary, a phenomenon termed the light-time effect (LITE). We aim to refine two aspects of the mathematical treatment of LITE. First, we provide both generalized and more accurate analytic formulation describing the light-travel time in the binary system itself presented in previous works. Second, we analytically estimate the so far neglected coupling of LITE with the dynamical interaction of the binary orbit with the motion of the third star. Our principal results are given in a simple analytical form, which is suitable for the analysis of photometric observations that require minimization over a multidimensional parameter space of the triple system. The leading correction to the traditional formulation of LITE due to the light-travel time in the binary system may be detectable for triple systems with a period ratio of $P_2/P_1\lesssim 20$, for which accurate photometric observations are available. On the other hand, the correction due to the dynamical coupling of the two orbits with $P_2$ periodicity is small, but may become relevant in the future.
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High Energy Astrophysical Phenomena

X-ray transients in the Chandra archive: Introducing the cumulative distribution discriminator (CuDiDi)

I. Saathoff and J. Larsson

X-ray transients on sub-observation timescales represent a diverse and underexplored class of astrophysical phenomena, from stellar flares and magnetar bursts to extragalactic fast transients and supernova shock breakouts. We present a systematic search for such events across 20,212 Chandra ACIS observations using a new detection pipeline that combines source identification, light-curve analysis, catalogue cross-matching, and a novel statistical classifier, the cumulative distribution discriminator (CuDiDi). From 1420 initial candidates, we identified a high-confidence golden sample of 765 transients spanning a broad range of timescales, fluxes, and spectral shapes. The candidates are distributed across the whole sky and show a wide range of durations with a median of 10 ks. A subset of fast events lasting < 30 s displays very soft spectra and is likely due to flaring dwarf stars, although extragalactic phenomena cannot be ruled out for all of them. The comparison with previously published samples showed that CuDiDi identifies most known transients while imposing somewhat stricter variability criteria, and it also extends the total sample of Chandra transients to include shorter events. We deliver a comprehensive catalogue of sub-observation Chandra X-ray transients and establish a general method for exploiting archival datasets to uncover rare short-lived high-energy phenomena.
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Astrophysics of Galaxies

Are "Changing-Look" Active Galactic Nuclei Special in the Coevolution of Supermassive Black Holes and their Hosts? II. The Case of Changing-Look Narrow-Line Seyfert 1 Galaxies

J. Wang, S. Jin, D. W. Xu et al. (+5 more)

The evolutionary role of the so-called “changing-look” (CL) active galactic nucleus (AGN), which is characterized by spectral-type transitions within $\sim10$ yr, has been suggested in the past few years. By focusing on CL-AGNs having spectra similar to those of broad-line Seyfert 1 galaxies, some authors have proposed that CL-AGNs tend to be at a special evolutionary stage associated with intermediate-to-old stellar populations. Here we attempt to verify this evolutionary role by extending the sample to CL narrow-line Seyfert 1 (NLS1) galaxies, which are believed to be “young” AGNs with a less massive supermassive black hole and high accretion rate. Combining the recent large NLS1 catalog provided by Paliya et al. (2024) and the SDSS-V DR19 spectral survey returns only three CL-NLS1s out of a parent sample of 884 objects, reinforcing the rarity of CL-NLS1s. Subsequent spectral analysis shows that the evolutionary role mentioned above still holds, although CL-NLS1s tend to occupy the young end of the intermediate-old population. Finally, we propose that off-center SDSS spectra caused by the “fiber drop” effect have great potential for determining the properties of the narrow-line region of NLS1s.
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All authors J. Wang, S. Jin, D. W. Xu, WeiKang Zheng, Thomas G. Brink, S. Komossa, 1 Alexei V. Filippenko, J. Y. Wei

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

Dark energy and accelerating cosmological evolution in a Universe with a Weylian boundary

Tiberiu Harko and Shahab Shahidi

We investigate the influence of boundary terms in gravitational field theories, by considering that in the Einstein-Hilbert action the boundary can be described by a non-metric Weyl-type geometry. The gravitational action and the the field equations, are thus generalized to include new geometrical terms, coming from the non-metric nature of the boundary, and depending on the Weyl vector, and its covariant derivatives. The field equations obtained within this framework generalize the standard Einstein equations by including in their mathematical structure the Weyl vector, and its covariant derivatives. As an applications of the general formalism we investigate the cosmological evolution in a flat FLRW geometry. We obtain the generalized Friedmann equations, which contain extra terms depending on the Weyl vector and its derivatives, arising due to the presence of the Weylian boundary, and which describe an effective, time dependent dark energy. By imposing to the dark energy an equation of state parameter of the Barboza-Alcaniz type, the Friedmann equations can be solved numerically. We compare the predictions of the Weylian boundary gravitational theory with late-time observational data and the predictions of the $\Lambda$CDM paradigm. Our results show that the Weylian boundary cosmological models give a good description of the observational data, and they can reproduce almost exactly the predictions of the $\Lambda$CDM paradigm. Hence, the extension of gravitational theories through the addition of Weylian boundary terms, in which dark energy has a purely geometric origin, emerges as a viable alternative to standard general relativity.
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Cosmology and Nongalactic Astrophysics

Inflationary phase transitions in the early Universe: A Bayesian study with space-based gravitational-wave detectors

Qingyuan Liang, Chen Yang, Haipeng An et al. (+1 more)

Inflationary phase transitions can generate a stochastic gravitational-wave background that probes primordial physics. We study the detectability and parameter reconstruction of such a signal with a space-based gravitational-wave detector. Using a Taiji-like mission as a benchmark, we construct a realistic data-analysis framework that includes instrumental noise, astrophysical foregrounds and backgrounds, and the $A$, $E$, and $T$ time-delay interferometry channels. The target signal is described in a minimal, model-independent form and analyzed using both Fisher-matrix forecasts and Bayesian inference with nested sampling. We quantify detection significance and parameter-recovery thresholds, showing that, while detection is achievable at moderate signal-to-noise ratios, stronger signals provide more reliable parameter reconstruction. These results offer a realistic assessment of the capability of future space-based missions to probe inflationary phase transitions through stochastic gravitational radiation.
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All authors Qingyuan Liang, Chen Yang, Haipeng An, Huai-Ke Guo

Earth and Planetary Astrophysics

The fragility of the Uranian moons during the giant planet instability

Matthew S. Clement, Nathan A. Kaib, Andre Izidoro et al. (+1 more)

It is thought that, sometime after their formation, the solar system's giant planets experienced a dynamical instability that caused their orbits to excite, diverge, and ejected one or more objects with masses comparable to the ice giants. A key feature of this model is that the planets experience encounters with other planetary bodies, and these encounters facilitate the capture of nearby small bodies as irregular satellites. Instability simulations indicate that planet-planet encounter distances can typically fall below 0.1 au, which is only roughly an order of magnitude larger than the radial extent of the modern planets' regular satellite systems. In this paper we model the effects of these encounters on the dynamical stability of the regular moons of Jupiter and Uranus. We tested encounter histories from 122 plausible outer solar system dynamical histories. We find that the survival probability for the Jovian and Uranian moon systems are both less than 15%. Moreover, we only identify one case where both Uranus and Jupiter's large satellites consistently survive the same instability. Interestingly, Jupiter's moons are most likely to survive in instabilities initialized with two smaller extra ice giants, and cases with one larger additional planet provide more favorable conditions for Uranian system survival. In either case, if Uranus encounters another ice giant at D<0.02 au, or one of the gas giants at D<0.1 au, satellite system destruction is effectively guaranteed. Wider encounters can also affect the system, particularly when they occur successively. Since the Laplace resonance likely would not be in place today if Jupiter's moons experienced an instability that led to collisions, our results indicate that Uranus' moons were likely perturbed to the point of collisions at least twice: as a result of both the impact that tilted the planet and the giant planet instability.
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All authors Matthew S. Clement, Nathan A. Kaib, Andre Izidoro, Rogerio Deienno

High Energy Astrophysical Phenomena

The second H.E.S.S. gamma-ray burst catalogue: 15 years of observations with the H.E.S.S. telescopes

A. Acharyya, F. Aharonian, C. Arcaro et al. (+144 more)

Recent observational efforts using imaging atmospheric Cherenkov telescopes (IACTs) have led to firm detections of very-high-energy (VHE) signals from bright gamma-ray bursts (GRBs), often at moderate redshifts. This work presents 15 years of H.E.S.S. GRB observations and examines their implications through population comparisons and selected modelling cases. GRBs are a key science target of the High Energy Stereoscopic System (H.E.S.S.). With a low-energy threshold ($\lesssim$100 GeV) and rapid repointing capabilities, H.E.S.S. can begin follow-up observations within tens of seconds after a GRB trigger, covering the late prompt or early afterglow phases. We report GRB follow-up observations with H.E.S.S. from 2004 to 2019, which resulted in no significant VHE signals (aside from the detections of GRB~180720B and GRB~190829A). The resulting upper limits comprise the largest set available for GRBs at VHE. A subset of bursts with favourable conditions were selected for X-ray analysis and emission modelling. Population studies were performed to compare detected and non-detected GRBs. The results indicate that VHE-detected GRBs are not a distinct population, but tend to feature luminous X-ray emission and favourable redshift and observing conditions. This highlights the potential of next-generation IACTs such as the Cherenkov Telescope Array Observatory (CTAO), whose lower energy threshold will enhance the detection of fainter and more distant GRBs.
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All authors A. Acharyya, F. Aharonian, C. Arcaro, H. Ashkar, M. Backes, V. Barbosa Martins, R. Batzofin, Y. Becherini, D. Berge, K. Bernlöhr, M. Böttcher, C. Boisson, J. Bolmont, J. Borowska, F. Brun, B. Bruno, C. Burger-Scheidlin, S. Casanova, J. Celic, M. Cerruti, S. Chandra, A. Chen, M. Chernyakova, J. O. Chibueze, O. Chibueze, T. Collins, B. Cornejo, G. Cotter, J. Damascene Mbarubucyeye, I.D. Davids, J. de Assis Scarpin, M. de Bony de Lavergne, M. de Naurois, E. de Oña Wilhelmi, A. G. Delgado Giler, J. Devin, A. Djannati-Ataï, J. Djuvsland, A. Dmytriiev, K. Egberts, K. Egg, J.-P. Ernenwein, C. Escañuela Nieves, M. D. Filipovic, G. Fontaine, S. Funk, S. Gabici, Y.A. Gallant, M. Genaro, J.F. Glicenstein, J. Glombitza, M.-H. Grondin, L. Heckmann, B. Heß, J.A. Hinton, W. Hofmann, T. L. Holch, M. Holler, D. Horns, Z. Huang, M. Jamrozy, F. Jankowsky, I. Jaroschewski, D. Jimeno Sanchez, I. Jung-Richardt, E. Kasai, K. Kasprzak, K. Katarzyński, D. Kerszberg, B. Khélifi, W. Kluzniak, N. Komin, K. Kosack, D. Kostunin, R.G. Lang, S. Lazarević, M. Lemoine-Goumard, J.-P. Lenain, P. Liniewicz, A. Luashvili, J. Mackey, D. Malyshev, D. Malyshev, V. Marandon, M. Mayer, A. Mehta, A. Mikhno, A.M.W. Mitchell, R. Moderski, M.O. Moghadam, L. Mohrmann, A. Montanari, E. Moulin, J. Niemiec, P. O'Brien, L. Olivera-Nieto, S. Panny, M. Panter, R.D. Parsons, U. Pensec, P. Pichard, S. Pita, G. Pühlhofer, M. Punch, A. Quirrenbach, M. Regeard, A. Reimer, O. Reimer, I. Reis, H. Ren, B. Reville, F. Rieger, G. Rowell, B. Rudak, E. Ruiz-Velasco, K. Sabri, V. Sahakian, H. Salzmann, D.A. Sanchez, A. Santangelo, M. Sasaki, F. Schüssler, M. Senniappan, J.N.S. Shapopi, W. Si Said, H. Sol, S. Spencer, Ł. Stawarz, S. Steinmassl, T. Tanaka, A.M. Taylor, G. L. Taylor, R. Terrier, M. Tsirou, T. Unbehaun, C. van Eldik, M. Vecchi, C. Venter, J. Vink, T. Wach, S.J. Wagner, A. Wierzcholska, M. Zacharias, A.A. Zdziarski, W. Zhong, S.J. Zhu, A. Zech

High Energy Astrophysical Phenomena

Narrow iron- and nickel-K absorption lines from the eclipsing low-mass X-ray binary AX~J1745.6$-$2901

Kojiro Tanaka, Yoshitomo Maeda, Ryota Tomaru et al. (+23 more)

We report the presence of a highly ionized absorber in the transient, eclipsing low-mass X-ray binary AX J1745.6-2901, observed from Feb. 26 to 29, 2024 with XRISM's Resolve and Xtend instruments. During a soft/high state without dips, Resolve's high spectral resolution (E/dE ~ 1000, full width at half maximum) revealed narrow velocity widths (sigma ~ 110 km/s) for Fe XXVI and Ni XXVIII lines, even with low photon statistics. These widths are consistent with binary orbital motion. The observed modest blueshift velocity (~160 km/s) indicates that the absorber is located sufficiently far from the neutron star (> 10^9 cm), so that gravitational redshift effects are not dominant. On the other hand, broad-band spectral analysis using a photoionized plasma model applied to the Xtend data constrains the absorber to lie within a radius of < 10^9.5 cm, as inferred from the upper limits of the best-fit ionization parameter (log xi ~ 4.4) and the large column density (~ 1.6 x 10^24 cm^-2). At this distance, the observed outward velocity of the absorber is about an order of magnitude smaller than the escape velocity from the neutron star.
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All authors Kojiro Tanaka, Yoshitomo Maeda, Ryota Tomaru, Lia Corrales, María Díaz Trigo, Chris Done, Tadayasu Dotani, Manabu Ishida, Satoru Katsuda, Yoshiaki Kanemaru, Richard Kelley, Aya Kubota, Hironori Matsumoto, Masayoshi Nobukawa, Megumi Shidatsu, Randall Smith, Hiromasa Suzuki, Hiromitsu Takahashi, Yohko Tsuboi, Hideki Uchiyama, Shigeo Yamauchi, Anje Yoshimoto, Q. Daniel Wang, Jon M. Miller, Frederick S. Porter, Shinya Yamada

Solar and Stellar Astrophysics

A quasi-star is born: formation and evolution of accreting quasi-stars as a pathway to Little Red Dots at non-zero metallicity

J. Roman-Garza, C. Charbonnel, D. Schaerer et al. (+5 more)

The recently discovered Little Red Dots identified by the James Webb Space Telescope are compact high-redshift sources whose properties have motivated models involving black holes embedded within optically thick gaseous envelopes. We investigate their rest-frame optical emission by modeling quasi-stars, i.e. stellar envelopes powered by accretion onto a central black hole, formed from rapidly accreting proto-stars that reach the supermassive star regime ($>10^4$~\Msun) before undergoing general relativistic instability. We compute stellar evolution models with mass gain rates of 0.01, 0.1, and 1~\Msun/yr and metallicities $Z=0$-$0.01$. For accretion rates $\ge0.1$~\Msun/yr, stars remain nearly fully convective with $T_\mathrm{eff}\sim4000$-$9000$~K. General relativistic instability occurs at $M_\star\sim3.5\times10^4$~\Msun\ ($6.8\times10^4$~\Msun) for $\dot{m}=0.1$~\Msun/yr (1~\Msun/yr), at $L\sim10^9$~\Lsun. Assuming the black hole supports the envelope until complete accretion ($M_{\rm BH,max}/M_{\rm QS}=1$), quasi-stars reach maximum lifetimes of $10^7$-$10^8$~yr, $\sim100$-$1000$ times longer than their progenitors. Their formation and evolution are nearly independent of metallicity. Matching our models to Little Red Dots at $z<4.5$ ($L_\mathrm{bol}\sim10^{9.5}$-$10^{11.5}$~\Lsun) implies quasi-star masses of $10^{4.5}$-$10^{6.5}$~\Msun, while the minimum observed luminosity requires progenitor accretion rates $\gtrsim0.1$~\Msun/yr. Our models support quasi-stars as the origin of Little Red Dot optical emission and constrain their masses, lifetimes, progenitor environments, and luminosities. Our models offer a framework supporting quasi-stars as the source of Little Red Dot optical emission, and provide insights into their lifetimes, composition, progenitor's environment as well on their minimum and maximum observed luminosities.
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All authors J. Roman-Garza, C. Charbonnel, D. Schaerer, T. Fragos, E. Cenci, R. Marques-Chaves, P. Oesch, M. Xiao

High Energy Astrophysical Phenomena

Cherenkov Neutrino Telescopes: Recent Progress and Next Steps

Aya Ishihara

Neutrino telescopes provide a unique observational gateway to the high-energy universe, enabling the study of cosmic accelerators and extreme environments that remain inaccessible to the other high-energy messengers. Although they share core detection principles with neutrino experiments in particle physics, such as the observation of Cherenkov radiation, their scientific objectives and operational constraints diverge markedly. This paper reviews the motivations behind astrophysical neutrino detection, outlines key design strategies across various media and deployment environments, and highlights the critical role of neutrino telescopes in the context of multimessenger astronomy. In particular, we emphasize their potential to illuminate the origins of cosmic rays and to probe the mechanisms driving the most energetic phenomena in the universe.
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Cosmology and Nongalactic Astrophysics

Unimodular Diffusion and Interacting Vacuum Cosmology

Gopal Kashyap and Naveen K. Singh

We investigate the correspondence between unimodular diffusion cosmology and interacting dark sector models at the background and linear perturbation levels. In the diffusion framework, the effective cosmological constant becomes time dependent, $\Lambda(t)$, sourced by a diffusion current. We show that at the background level this framework can be mapped onto interacting dark energy models with $w=-1$ and energy transfer $Q$. Using two common parameterizations, $Q = \xi H \rho_{\rm de}$ and $Q = \xi H \rho_{\rm dm}$, and data from supernovae, DESI BAO, cosmic chronometers, and CMB distance priors, we find $\xi = -0.0197 \pm 0.0076$ for the vacuum-coupled case, while the matter-coupled case gives a best-fit $\xi = 0.0018$ with comparable goodness of fit. At the level of linear perturbations, however, the diffusion framework is consistent only with interacting vacuum models having homogeneous energy transfer ($Q \propto \rho_{\rm de}$ with $\delta Q=0$), thereby breaking the degeneracy with more general interacting dark energy scenarios. Including redshift-space distortion data, we obtain $\xi = -0.0147 \pm 0.0075$, consistent with $\Lambda$CDM ($\xi=0$) at $2\sigma$. The inferred clustering amplitude is $S_8 = 0.782 \pm 0.026$ for the diffusion model, compared to $S_8 = 0.77 \pm 0.025$ for $\Lambda$CDM under the same dataset, indicating a modest but non-negligible impact on structure growth.
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