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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 28 October

Solar and Stellar Astrophysics

Alpha Core-Beam Origin in Low-$\beta$ Solar Wind Plasma: Insights from Fully Kinetic Simulation

Luca Pezzini, Fabio Bacchini, Andrei N. Zhukov et al. (+2 more)

In-situ observations of the fast solar wind in the inner-heliosphere show that minor ions and ion sub-populations often exhibit distinct drift velocities. Both alpha particles and proton beams stream at speeds that rarely exceed the local Alfvén speed relative to the core protons, suggesting the presence of instabilities that constrain their maximum drift. We aim to propose a mechanism that generates an alpha-particle beam through non-linear Landau damping, primarily driven by the relative super-Alfvénic drift between protons and alpha particles. To investigate this process, we perform one-dimensional, fully kinetic particle-in-cell simulations of a non-equilibrium multi-species plasma, complemented by its linear theory to validate the model during the linear phase. Our results provide clear evidence that the system evolves by producing an alpha-particle beam, thereby suggesting a local mechanism for alpha-beam generation via non-linear Landau damping.
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All authors Luca Pezzini, Fabio Bacchini, Andrei N. Zhukov, Giuseppe Arrò, Rodrigo A. Lopez

Earth and Planetary Astrophysics

Emergence of streamers in simulations of late infall

L.-A. Hühn and C. P. Dullemond

Growing observational evidence suggests that Class II protoplanetary disks may undergo substantial interactions with their environment in the form of late infall. This mass inflow predominantly manifests itself in the form of so-called streamers: filaments and arcs of gas connecting large-scale, extended gas structures to disk scales. Prevalent late infall has far-reaching consequences for planet formation theory, challenging the long-standing treatment of evolved disks in isolation. In this work, we investigate the emergence of late-infall streamers in different formation scenarios, their morphology and multiplicity, as well as their dependence on environmental conditions. We conduct this investigation by performing 3D hydrodynamical simulation using the grid-based code FARGO3D, which we post-process to obtain synthetic observations using the Monte Carlo radiative transfer code RADMC3D. We find that, while a late infall event in the form of a single encounter with a "cloudlet" of gas can produce a streamer via an interplay between the fallback of bound material and shocks, such features dissipate quickly, on a timescale of ~10 kyr. Furthermore, we find that streamers can also form naturally in a turbulent, dense environment without the need for such encounters, which could act to reconcile short-lived streamers with ubiquitous detection of these structures. Here, we find multiple co-existing streamers for a disk velocity relative to the interstellar medium of $v_\mathrm{sys}=0.5~\mathrm{km}~\mathrm{s}^{-1}$ and a turbulent velocity dispersion of $\sigma_\mathrm{turb}=0.5~\mathrm{km}~\mathrm{s}^{-1}$. We find considerable dependence of the streamer morphology on the environment, which may act as a utility to constrain the physical conditions of the gas surrounding planet-forming disk, and therefore the conditions under which planets form.
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Earth and Planetary Astrophysics

Bistability, Oscillations, and Multistability on Hycean Planets

Yichen Gao, Daniel D. B. Koll and Feng Ding

Hycean planets are hypothetical exoplanets characterized by $H_2O$ oceans and $H_2$-rich atmospheres. These planets are high-priority targets for biosignature searches, as they combine abundant surface liquid water with easy-to-characterize $H_2$-rich atmospheres. Perhaps their most unusual climate feature is convective inhibition, which can dramatically alter a planet's temperature structure. However, so far hycean planets have mostly been investigated using 1D models that do not account for convective inhibition, and its effects are still poorly understood. This work develops pen-and-paper theory to analyze the effects of moist convective inhibition on hycean planets. The theory is tested and verified against a 1D radiative-convective model. We show that hycean planets near the onset of convective inhibition can exhibit either bistability or oscillations, due to the inhibition layer's trapping of heat and moisture. Meanwhile, hot hycean planets exhibit multistability, in which the inhibition layer and surface climate show multiple stable equilibria due to the lack of constraints on the water cycle inside the inhibition layer. The water cycle inside the inhibition layer is influenced by numerous processes that are challenging to resolve in 1D, including turbulent diffusion, convective overshoot and large-scale circulations. Our results demonstrate that hycean planets have unexpectedly rich climate dynamics. Meanwhile, previous claims about hycean planets should be treated with caution until confirmed with more self-consistent 1D and 3D models; this includes the claim that K2-18b might be habitable, and the proposal to infer $H_2O$ oceans on sub-Neptunes from JWST measurements of chemical species in their upper atmospheres.
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Instrumentation and Methods for Astrophysics · Cross-listed from cs.DC

Towards Exascale Computing for Astrophysical Simulation Leveraging the Leonardo EuroHPC System

Nitin Shukla, Alessandro Romeo, Caterina Caravita et al. (+16 more)

Developing and redesigning astrophysical, cosmological, and space plasma numerical codes for existing and next-generation accelerators is critical for enabling large-scale simulations. To address these challenges, the SPACE Center of Excellence (SPACE-CoE) fosters collaboration between scientists, code developers, and high-performance computing experts to optimize applications for the exascale era. This paper presents our strategy and initial results on the Leonardo system at CINECA for three flagship codes, namely gPLUTO, OpenGadget3 and iPIC3D, using profiling tools to analyze performance on single and multiple nodes. Preliminary tests show all three codes scale efficiently, reaching 80% scalability up to 1,024 GPUs.
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All authors Nitin Shukla, Alessandro Romeo, Caterina Caravita, Michael Redenti, Radim Vavrik, Lubomir Riha, Andrea Mignone, Marco Rossazza, Stefano Truzzi, Luca Tornatore, Antonio Ragagnin, Tiago Castro, Geray S. Karademir, Klaus Dolag, Pranab J. Deka, Fabio Bacchini, Rostislav-Paul Wilhelm, Daniele Gregori, Elisabetta Boella

High Energy Astrophysical Phenomena

Vortex Creep Heating in Neutron Star Cooling: New Insights into Thermal Evolution of Heavy Neutron Stars

Yoonhak Nam and Kazuyuki Sekizawa

Neutron stars provide unique laboratories for probing physics of dense nuclear matter under extreme conditions. Their thermal and luminosity evolution reflects key internal properties such as the equation of state (EoS), nucleon superfluidity and superconductivity, envelope composition, and magnetic field, and so on. Recent observations [e.g., V. Abramkin et al., ApJ 924, 128 (2022)] have revealed unexpectedly warm old neutron stars, which cannot be explained by standard neutrino-photon cooling models. The failure of the standard cooling models implies the presence of additional internal heating mechanism. Building on the previous study [M. Fujiwara et al., JCAP 03, 051 (2024)], which proposed vortex creep heating (VCH) from the frictional motion of superfluid vortices as a viable mechanism, we extend the cooling framework to include both VCH and direct Urca (DUrca) processes. These are implemented in our code to explore their combined impact, particularly for massive neutron stars where DUrca operates. By varying rotational parameters ($P$, $\dot{P}$, $P_0$), EoS models (APR, BSk24), pairing gaps, and envelope compositions, we examine how heating-cooling interplay shapes the temperature evolution. Our results show that VCH can substantially mitigate the rapid cooling driven by DUrca, offering new evolutionary pathways for massive neutron stars.
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Astrophysics of Galaxies

Self-supervised Synthetic Pretraining for Inference of Stellar Mass Embedded in Dense Gas

Keiya Hirashima, Shingo Nozaki and Naoto Harada

Stellar mass is a fundamental quantity that determines the properties and evolution of stars. However, estimating stellar masses in star-forming regions is challenging because young stars are obscured by dense gas and the regions are highly inhomogeneous, making spherical dynamical estimates unreliable. Supervised machine learning could link such complex structures to stellar mass, but it requires large, high-quality labeled datasets from high-resolution magneto-hydrodynamical (MHD) simulations, which are computationally expensive. We address this by pretraining a vision transformer on one million synthetic fractal images using the self-supervised framework DINOv2, and then applying the frozen model to limited high-resolution MHD simulations. Our results demonstrate that synthetic pretraining improves frozen-feature regression stellar mass predictions, with the pretrained model performing slightly better than a supervised model trained on the same limited simulations. Principal component analysis of the extracted features further reveals semantically meaningful structures, suggesting that the model enables unsupervised segmentation of star-forming regions without the need for labeled data or fine-tuning.
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Solar and Stellar Astrophysics

Radiatively Cooled Binary Mass Transfer: Flow Structure, Luminosities, and L2 Outflows Across Mass Transfer Rates

Peter Scherbak, Wenbin Lu and Jim Fuller

High rates of stable mass transfer (MT) occur for some binary star systems, resulting in luminous transients and circumbinary outflows (CBOs). We perform hydrodynamical simulations of a $10 \ M_\odot$ donor star and a $5\ M_\odot$ point mass accretor, incorporating approximate effects of radiative cooling. By varying the orbital separation of the system, we probe MT rates between $10^{-5}$ and $10^{-1} M_\odot$/yr. Mass flows from the donor into a disk around the accretor, with significant equatorially concentrated outflows through the outer Lagrange point L2 occurring for MT rates $\gtrsim 10^{-3} M_\odot$/yr, while the MT remains mostly conservative for lower MT rates. In all cases, any outflowing gas approximately carries the specific angular momentum of L2. The gas cooling luminosity $L$ and temperature increases with MT rate, with $L \sim 10^{5} L_\odot$ and $T \sim 10^{4}$ K for simulations featuring the strongest outflows, with contributions from both the CBO and the accretor's disk. The most luminous transients associated with mass outflows will be rare due to the high MT rate requirement, but generate significant optical emission from both near the accretor and the CBO.
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High Energy Astrophysical Phenomena

Decadal brightening in the northeastern non-thermal filament of Cassiopeia A

Nao Kominato, Toshiki Sato, Yusuke Sakai et al. (+2 more)

We present the decadal brightening of non-thermal emission flux in the northeastern filament of the young supernova remnant Cassiopeia A (Cas A), which highlights dynamic processes in the forward shock. This filament, characterized by the highest particle acceleration rate among Cas A's outer shells, offers an exceptional opportunity to investigate underlying astrophysical mechanisms. Since 2000, the non-thermal flux has increased by several tens of percent before plateauing, while the spectral shape has remained largely unchanged. Over the past two decades, the filament's morphology has evolved significantly, splitting into two distinct sections. Detailed analysis reveals contrasting behaviors: one section shows a flux increase followed by saturation, while the other maintains a steady flux. These differences likely arise from nonlinear effects, including magnetohydrodynamic interactions influenced by magnetic field orientation, interactions with surrounding material, and complex fluid dynamics associated with young supernova remnants. The localized evolution of this filament, captured with high spatial resolution, provides critical insights into the temporal dynamics of non-thermal particles and the generation of cosmic rays from asymmetric supernova explosions.
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All authors Nao Kominato, Toshiki Sato, Yusuke Sakai, Ryota Hayakawa, Shinya Yamada

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

Relaxed constraints for dark matter with axial coupling to a dark photon

X. G. Wang and A. W. Thomas

We present a new model of the dark sector involving Dirac fermion dark matter, with axial coupling to a dark photon which provides a portal to Standard Model particles. In the non-relativistic limit, this implies that the dominant effective operator relevant to direct detection is ${\cal O}_8$. The resulting event rate for direct detection is suppressed by either the dark matter velocity or the momentum transfer. In this scenario there are much wider regions of the dark parameter space that are consistent with all of the existing constraints associated with thermal relic density, direct detection and collider searches.
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Cosmology and Nongalactic Astrophysics

The Most Probable Behaviour of the Dark Energy Equation of State Indicates a Thawing Quintessence Field: Tomographic Alcock-Paczyński Test with Redshift-Space Correlation Function II

Fuyu Dong and Changbom Park

We apply an extended Alcock-Paczyński (AP) test to the Sloan Digital Sky Survey data to constrain the dark energy models with the Chevallier-Polarski-Linder (CPL) parametrization of the dark energy equation of state. The extended AP test method uses the full shape of redshift-space two-point correlation funcion(CF) as the standard shape in order to measure the expansion history of the universe. We calibrate the standard shape by using the cosmology-dependent nonlinear evolution of the CF shape in the Multiverse simulations. Further validation of the method and calibration of possible systematics are performed based on mock samples from the Horizon Run 4 simulation. Using the AP test alone, we constrain the flat CDM plus CPL-type dark energy model (flat $w^{\rm CPL}$CDM) to have $\Omega_m=0.290_{-0.031}^{+0.029}$, $w_0=-0.800_{-0.100}^{+0.208}$, and $w_a=-0.238_{-0.972}^{+0.650}$. When combined with other results from the low-redshift universe, such as the Pantheon$+$ supernova compilation and DESI BAO data, the constraint on dark energy becomes $w_0=-0.857_{-0.042}^{+0.051}$, and $w_a=-0.153_{-0.356}^{+0.347}$. The best-fit $w^{CPL}(z)$ suggests no phantom-divide crossing at $z<0.7$, and the dark energy behaviour is consistent with a thawing quintessence field. It is only when the CMB data are combined with late-time cosmological probes that a phantom-divide crossing at low redshift is favored.
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Instrumentation and Methods for Astrophysics

CSST Slitless Spectra: Target Detection and Classification with YOLO

Yingying Zhou, Chao Liu, Hao Tian et al. (+2 more)

Addressing the spatial uncertainty and spectral blending challenges in CSST slitless spectroscopy, we present a deep learning-driven, end-to-end framework based on the You Only Look Once (YOLO) models. This approach directly detects, classifies, and analyzes spectral traces from raw 2D images, bypassing traditional, error-accumulating pipelines. YOLOv5 effectively detects both compact zero-order and extended first-order traces even in highly crowded fields. Building on this, YOLO11 integrates source classification (star/galaxy) and discrete astrophysical parameter estimation (e.g., redshift bins), showcasing complete spectral trace analysis without other manual preprocessing. Our framework processes large images rapidly, learning spectral-spatial features holistically to minimize errors. We achieve high trace detection precision (YOLOv5) and demonstrate successful quasar identification and binned redshift estimation (YOLO11). This study establishes machine learning as a paradigm shift in slitless spectroscopy, unifying detection, classification, and preliminary parameter estimation in a scalable system. Future research will concentrate on direct, continuous prediction of astrophysical parameters from raw spectral traces.
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All authors Yingying Zhou, Chao Liu, Hao Tian, Xin Zhang, Nan Li

Earth and Planetary Astrophysics

Lunar Navigation System Optimization for Targeted Coverage with Semi-Analytical Station Keeping Model and Earth-GPS Integration

Rameez A. Malik and Yang Yang

The design of an indigenous Lunar Navigation Satellite System (LNSS) is receiving growing attention due to the surge in planned lunar missions and the limited accessibility of Earth-based Global Navigation Satellite Systems (GNSS) in the cislunar environment. Several studies have explored LNSS architecture using geometric analysis in both near and distant lunar orbits. The existing LNSS optimization efforts have primarily focused on global lunar coverage using analytical station-keeping models with low accuracy. Furthermore, current south pole-focused research is restricted to Elliptical Lunar Frozen Orbits (ELFOs) and lacks comprehensive optimization approach. Additionally, integration with Earth GNSS systems for ephemeris computation and time synchronization has not been adequately addressed in prior studies. In this work, we present a comprehensive LNSS mission design framework based on evolutionary multi-objective optimization integrated with a high-fidelity numerical lunar orbit propagation model. The optimization simultaneously considers navigation performance in the lunar south pole region, semi-analytical continuous station-keeping maneuver model for realistic dV estimate, and GPS-LNSS integration analysis parameters. The resulting Pareto front offers a diverse set of LNSS configurations that balance coverage, accuracy, and dV requirements. Notably, the optimization identifies diverse non-frozen elliptical orbit solutions that achieve over 90% south pole coverage with acceptable navigation accuracy using as few as six satellites and dV of less than 0.4 km/s per satellite per year. This represents a significant reduction in constellation size compared to previous studies, offering a cost-effective yet operationally efficient solution for future LNSS missions.
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High Energy Astrophysical Phenomena

Eclipsed X-ray Bursts from Magnetar SGR J1935+2154 and the Fireball Measurements

Sheng-Lun Xie, Aming Chen, Yun-Wei Yu et al. (+17 more)

In theory, burst activity of the magnetar can lead to the formation of fireballs trapped by the magnetic field and corotating with the star. However, the smoking-gun observational evidence of the fireball is elusive. We envisage that the fireball emission should occasionally be eclipsed by the magnetar, especially when the burst duration is comparable to the magnetar's spin period. In this work, we first discover a peculiar type of burst whose light curve has a plateau-like feature among the long bursts of the magnetar SGR J1935+2154 detected by GECAM and Fermi/GBM. Then, based on these bursts, we identified four burst candidates with eclipse-like characteristics. By fitting their light curves with the eclipse fireball model, the viewing angle of the magnetar relative to its spin axis is estimated to be $17^\circ \pm 10^\circ$, and the distances from the fireballs to the magnetar are found to be more than 5 times the magnetar's radius, indicating that the fireballs are suspended in the magnetosphere rather than adhering to the magnetar surface. Furthermore, we find that this configuration is well consistent with the implication of the cyclotron resonance scattering feature we found in their spectra. Our results suggest that some intermediate X-ray bursts may originate from magnetic reconnection within the magnetosphere rather than the starquake.
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All authors Sheng-Lun Xie, Aming Chen, Yun-Wei Yu, Shao-Lin Xiong, Hua Feng, Shuang-Nan Zhang, Zi-Gao Dai, Wang-Chen Xue, Ming-Yu Ge, Xiao-Bo Li, Liang-Duan Liu, Jia-Cong Liu, Wen-Jun Tan, Chen-Wei Wang, Shu-Xu Yi, Peng Zhang, Yan-Qiu Zhang, Zhen Zhang, Chao Zheng, Xiao-Ping Zheng

High Energy Astrophysical Phenomena

Diverse Emission Patterns from Precessing Super-Eddington Disks Formed in Tidal Disruption Events

Jin-Hong Chen, Lixin Dai, Kan Cheuk Kwan et al. (+2 more)

A tidal disruption event (TDE) occurs when a star passes within the tidal radius of a supermassive black hole (SMBH). In TDEs it is expected that the orbital angular momentum of the disrupted star is generally misaligned with the SMBH spin axis, which should result in a misaligned super-Eddington disk precessing around the SMBH spin axis due to the Lense-Thirring effect. In this paper, we investigate the distinct observational signatures produced from such TDE disks, by performing radiative transfer calculations upon previous super-Eddington disk simulations. We demonstrate that the precession of the disk and wind drive time-dependent obscuration and reprocessing of X-ray radiation. Depending on the orientation of the viewing angle of the observer and the tilt angle of the disk, four main types of variability are induced: 1) The smooth-TDEs: The emissions from these TDEs show no fluctuations; 2) The dimmer: The main emission type (X-ray or optical) stays the same, with small to moderate modulations of brightness; 3) The blinker: X-ray and optical emissions take turns to dominate in one cycle of precession, with dramatic changes in the X-ray fluxes. 4) The siren: X-ray and optical emissions take over each other twice per cycle, possibly with two different peak X-ray fluxes within one cycle. In all three scenarios, we observe an inverse correlation between X-ray and optical emissions. Our model provides a physical framework for interpreting TDE multi-wavelength variability through disk precession dynamics and gives an alternative interpretation to the interesting case of J045650.3-203750 which was suggested to be a repeated partial TDE previously.
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All authors Jin-Hong Chen, Lixin Dai, Kan Cheuk Kwan, Tom Man Kwan, Zijian Zhang

Astrophysics of Galaxies

How External Medium outside Prestellar Cores Affects Protostellar Growth: Variations in Accretion Rate and Evolution of Disks and Outflows

Shingo Nozaki and Masahiro N. Machida

We investigate how the external medium surrounding prestellar cores affects the star formation process by conducting three-dimensional resistive magnetohydrodynamic simulations. The initial cores follow critical Bonnor-Ebert profiles and are embedded in environments with different ambient densities. The simulations follow the evolution at least until the envelope mass within a radius equal to twice the critical Bonnor-Ebert radius drops to 35% of the initial cloud mass. We reveal that in environments with higher external density, enhanced mass inflow from the envelope leads to Bondi-like accretion as the protostellar mass increases. The continued inflow substantially increases the final stellar mass, resulting in star formation efficiencies that appear to exceed unity in dense environments. The external medium also influences the evolution of circumstellar disks and protostellar outflows: with the high-density external medium, disks grow rapidly but their mass becomes smaller relative to the protostellar mass, and the outflow is sustained over a long duration. However, the ratio of angular momentum removed by outflows and magnetic braking to that introduced by inflowing gas decreases with increasing external density. These results suggest that the density of the external medium regulates not only protostellar mass growth but also the inflow-outflow balance and angular momentum transport in magnetized, rotating star-forming cores.
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Instrumentation and Methods for Astrophysics

LBT Italia: Current Achievements and Future Directions

Silvia Tosi, Ester Marini, Felice Cusano et al. (+3 more)

The Large Binocular Telescope (LBT) is a world-leading astronomical observatory, where the italian partnership has played an important role in increasing the telescope's productivity, both through an optimized observing strategy and through peer-reviewed publications that are well recognized by the international astronomical community. This manuscript provides an updated overview of the active and past instruments at LBT, together with the key usage statistics. In particular, we analyze the operational performance recorded in the LBT Italia night logs during INAF's observing time and assess the scientific impact of each instrument. Between 2014 and 2025 LBT Italia produced an average of 14 referred publication per year, based on an annual average of 311 hours of on-sky time. This corresponds to approximately 2.2 nights of telescope time per publication. The results of this analysis are placed in an international context to evaluate the competitiveness of LBT, and we outline future perspective for scientific exploitation.
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All authors Silvia Tosi, Ester Marini, Felice Cusano, Andrea Rossi, Roberto Speziali, Roberta Carini

Astrophysics of Galaxies

Tracing Cloud Formation and Evolution Through 3D Magnetic Field Mapping

Mehrnoosh Tahani, Laura Fissel, Enrique Lopez Rodriguez et al. (+1 more)

We propose to use the unprecedented polarization sensitivity of PRIMA's PRIMAger Polarization Imager and its high resolution in Band 1 (92 $\mu$m) to map magnetic fields across two contrasting molecular cloud environments: the well-studied Perseus cloud and the isolated Musca filament. This comparative study will leverage the existing VLA radio observations that provide line-of-sight magnetic field component of the Perseus cloud, along with upcoming POSSUM survey results for Musca, to construct the first detailed 3D magnetic field vector maps at sub-parsec resolution. Perseus, with its known formation history through interstellar structure (e.g., bubble) interactions, will reveal how magnetic fields evolve during active star formation phases, while Musca, an isolated filament with lower star-formation activity, will show magnetic field morphology in early evolutionary stages. With PRIMA's resolution of 0.01 pc for Perseus and $<0.01$ pc for Musca, we will resolve magnetic field structures at scales necessary for understanding cloud fragmentation and star formation efficiency, and the roles that magnetic fields play in these processes. Our survey will require approximately 1438 hours to cover 42 deg$^2$ of Perseus and 12 deg$^2$ of Musca. With this, we aim to provide the first comprehensive view of how environment and evolutionary state may influence magnetic field evolution in molecular clouds and how magnetic fields influence cloud formation, fragmentation, and star formation.
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All authors Mehrnoosh Tahani, Laura Fissel, Enrique Lopez Rodriguez, Kate Pattle

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

Symmetry Energy of 2+1-flavor dense quark matter from perturbative QCD

Isabella Danhoni, Yumu Yang, Mauricio Hippert et al. (+1 more)

The symmetry energy expansion was developed to connect isospin symmetric matter probed in nuclear experiments to asymmetric matter found in neutron stars. Using the isospin asymmetry derived from the Gell-Mann-Nishijima formula, we derive the symmetry energy expansion for quark matter that has unique properties compared to hadronic matter. To test our methods, we use perturbative Quantum Chromodynamics (pQCD) calculations at next-to-leading-order, where realistic quark masses can be included. We find that pQCD at electroweak equilibrium is not isospin symmetric but rather obtains a small skewness term in the symmetry energy expansion. We predict that if equations of state for nuclear matter must match pQCD results, then a non-monotonic dip in the symmetry energy would appear.
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All authors Isabella Danhoni, Yumu Yang, Mauricio Hippert, Jacquelyn Noronha-Hostler

High Energy Astrophysical Phenomena

Rest-frame Optical Spectroscopy of $z \sim 2$ Quasars with Steep Hard X-ray Spectral Shapes: X-ray Selection of Super-Eddington Accretion and Verification

Ying Chen, Bin Luo and Jian Huang

Super-Eddington accretion is a crucial phase in the growth of supermassive black holes. However, identifying super-Eddington accreting quasars observationally is challenging due to uncertain black-hole mass estimates and other complications. The Eddington ratio parameter does not represent accurately the accretion rate in the super-Eddington regime. On the other hand, super-Eddington accreting quasars appear to show large hard X-ray (rest-frame > 2 keV) power-law photon indices, and they also exhibit distinct optical spectral features including weak [O III] $\lambda 5007$ emission and strong Fe II emission. We test steep X-ray photon-index selection of super-Eddington accreting quasars by obtaining Palomar 200-inch Hale Telescope near-infrared spectra for a pilot sample of nine $\Gamma=2.0-2.6$ quasars at $z\approx1.4-2.5$. We derive H$\beta$-based single-epoch virial black-hole masses (median value $\rm 4.3 \times 10^{8}~M_{\odot}$) and Eddington ratios (median value 0.6). The Eddington ratio distribution is consistent with that of the comparison sample, which is a flux-limited sample of quasars at $z\approx1.5-3.5$ with near-infrared spectroscopy. But our super-Eddington candidates do show statistically weaker [O III] emission ($P_{\rm null}=0.0075$) and marginally stronger Fe II emission ($P_{\rm null}=0.06$). We also find one candidate with broad (width of 1960 km/s) and blueshifted (690 km/s) [O III] $\lambda 4959$ and [O III] $\lambda 5007$ lines, which probably originate from a strong [O III] outflow driven by super-Eddington accretion. Overall, the steep X-ray photon-index selection of super-Eddington accreting quasars appears promising. But a larger sample is needed to assess further the reliability of the selection.
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Monday 27 October

Solar and Stellar Astrophysics · Cross-listed from hep-ph

Weak interactions and the gravitational collapse

Domenec Espriu

The chart of nuclei could be enlarged with a branch describing neutron stars that are huge nuclei of a few solar masses held together by gravity force and sustained by the pressure due to the degenerate Fermi sea. We contend in this manuscript that yet another branch could be added: objects with a large weak charge, with masses around $10^{-3}$ solar masses and having radii of a few meters, very compact, only slightly larger than their Schwarzchild radius, and sustained by the pressure generated by the weak force due to $Z$ exchange. This interaction, insignificant in normal neutron stars, could become dominant when ultrahigh densities are reached due to the action of gravity and lead to stable configurations if the appropriate conditions are met. They would constitute a physical realization of the equation of state proposed by Zeldovich some decades ago.
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Solar and Stellar Astrophysics · Cross-listed from physics.ins-det

Towards a comprehensive study of the 14N(p,g)15O astrophysical key reaction: Description of the experimental technique including novel target preparation

A. Compagnucci, A. Formicola, M. Campostrini et al. (+46 more)

While the 14N(p,g)15O reaction plays a key role in the hydrogen-burning processes in various stellar conditions, its reaction rate is not known with sufficient precision. Therefore, the first scientific project at the recently launched Bellotti Ion Beam Facility of the Laboratori Nazionali del Gran Sasso was the measurement of the 14N(p,g)15O reaction cross section in the proton energy range between 250 and 1500 keV. In this paper, the experimental techniques are summarized with special emphasis on the description of solid state nitrogen target production and characterization. The first results of the reaction yield measured at 55 deg detection angle are also presented.
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All authors A. Compagnucci, A. Formicola, M. Campostrini, J. Cruz, M. Aliotta, C. Ananna, L. Barbieri, F. Barile, D. Bemmerer, A. Best, A. Boeltzig, C. Broggini, C.G. Bruno, A. Caciolli, F. Casaburo, F. Cavanna, G.F. Ciani, P. Colombetti, P. Corvisiero, L. Csedreki, T. Davinson, R. Depalo, A. Di Leva, Z. Elekes, F. Ferraro, Zs. Fülöp, A. Guglielmetti, C. Gustavino, Gy. Gyürky, G. Imbriani, M. Junker, M. Lugaro, P. Marigo, J. Marsh, E. Masha, R. Menegazzo, V. Paticchio, D. Piatti, P. Prati, D. Rapagnani, V. Rigato, D. Robb, L. Schiavulli, R. S. Sidhu, J. Skowronski, O. Straniero, T. Szücs, S. Turkat, S. Zavatarelli

High Energy Astrophysical Phenomena

Cosmological Evolution of Gamma Ray Bursts

Sujay Champati, Vahé Petrosian and Maria G. Dainotti

Gamma-ray bursts (GRBs) are classified as long (LGRBs) and short (SGRBs), with collapsars and compact-object mergers (NS-NS or NS-Black Holes) as progenitors, respectively. LGRBs are expected to follow the cosmic star formation rate (SFR), while SGRBs follow a delayed version of the SFR. However, this division has come under question, most prominently by observational evidence of an excess of LGRBs at low redshifts by several investigations, summarized in \cite{Petrosian_2024}. Two recent observations of low-redshift LGRBs show associations with kilonovae. Both of these indicate compact mergers as a potential source of LGRBs as well. Most results showing this separation are based on analyses of small (less than 200) samples of LGRBs with measured redshifts. The aim of this paper is to use a larger sample of LGRBs. The number of LGRBs with measured redshifts has increased by more than a factor of 2 over the last decade. To this data set we add a sample of LGRBs whose redshifts are estimated using a machine learning (ML) method (\cite{Narendra_2025}). To account for the observational selection bias due to redshift measurements, we use the non-parametric, non-binning Efron-Petrosian method to establish the degree of correlation between luminosity and redshift, the luminosity evolution, and then use the Lynden-Bell $C^-$ method to obtain the luminosity function. We find a low redshift excess for the larger sample with measured redshifts. Adding the sources with ML-estimated redshifts, which shows overabundance of the mid-range redshifts, the excess is reduced.
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Solar and Stellar Astrophysics

Six binary brown dwarf candidates identified by microlensing

Cheongho Han, Chung-Uk Lee, Ian A. Bond et al. (+57 more)

In this study, we analyze microlensing events from the 2023 and 2024 observing seasons to identify cases likely caused by binary systems composed of BDs. By applying criteria that the binary-lens events exhibit well-resolved caustics, short time scales ($t_{\rm E} \lesssim 9$ days), and have small angular Einstein radii ($\theta_{\rm E} \lesssim 0.17$~mas), we identify six candidate binary BD events: MOA-2023-BLG-331, KMT-2023-BLG-2019, KMT-2024-BLG-1005, KMT-2024-BLG-1518, MOA-2024-BLG-181, and KMT-2024-BLG-2486. Analysis of these events leads to models that provide precise estimates for both lensing observables, $t_{\rm E}$ and $\theta_{\rm E}$. We estimate the masses of the binary components through Bayesian analysis, utilizing the constraints from $t_{\rm E}$ and $\theta_{\rm E}$. The results show that for the events KMT-2024-BLG-1005, KMT-2024-BLG-1518, MOA-2024-BLG-181, and KMT-2024-BLG-2486, the probability that both binary components lie within the BD mass range exceeds 50%, indicating a high likelihood that the lenses of these events are binary BDs. In contrast, for MOA-2023-BLG-331L and KMT-2023-BLG-2019L, the probabilities that the lower-mass components of the binary lenses lie within the BD mass range exceed 50%, while the probabilities for the heavier components are below 50%, suggesting that these systems are more likely to consist of a low-mass M dwarf and a BD. The brown-dwarf nature of the binary candidates can ultimately be confirmed by combining the measured lens-source relative proper motions with high-resolution imaging taken at a later time.
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All authors Cheongho Han, Chung-Uk Lee, Ian A. Bond, Andrzej Udalski, Michael D. Albrow, Sun-Ju Chung, Andrew Gould, Youn Kil Jung, Kyu-Ha Hwang, Yoon-Hyun Ryu, Yossi Shvartzvald, In-Gu Shin, Jennifer C. Yee, Weicheng Zang, Hongjing Yang, Sang-Mok Cha, Doeon Kim, Dong-Jin Kim, Seung-Lee Kim, Dong-Joo Lee, Yongseok Lee, Byeong-Gon Park, Richard W. Pogge, Przemek Mróz, Michał K. Szymański, Jan Skowron, Radosław Poleski, Igor Soszyński, Paweł Pietrukowicz, Szymon Kozłowski, Krzysztof A. Rybicki, Patryk Iwanek, Krzysztof Ulaczyk, Marcin Wrona, Mariusz Gromadzki, Mateusz J. Mróz Michał Jaroszyński, Marcin Kiraga, Fumio Abe, David P. Bennett, Aparna Bhattacharya, Akihiko Fukui, Ryusei Hamada, Stela Ishitani Silva, Yuki Hirao, Asahi Idei, Shota Miyazaki, Yasushi Muraki, Tutumi Nagai, Kansuke Nunota, Greg Olmschenk, Clément Ranc, Nicholas J. Rattenbury, Yuki Satoh, Takahiro Sumi, Daisuke Suzuki, Takuto Tamaoki, Sean K. Terry, Paul J. Tristram, Aikaterini Vandorou, Hibiki Yama

High Energy Astrophysical Phenomena

Testing common approximations of neutrino fast flavor conversion

Erick Urquilla and Lucas Johns

A new chapter is opening in the theory of core-collapse supernovae and neutron star mergers as simulations of these events begin to incorporate fast flavor conversion (FFC) and other forms of neutrino flavor mixing. Using numerical experiments, we show that the approximations of FFC that have been implemented so far are limited by at least two of three factors: (1) approximating continuous evolution as a discrete sequence of instabilities, (2) using spatially homogeneous asymptotic states, and (3) assuming that FFC must be accompanied by instability. The factors we identify in this work will be important considerations as the research area progresses from initial exploratory studies to more quantitatively precise assessments.
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Astrophysics of Galaxies

MAGNUS II: Rotational support of massive early-type galaxies decreased over the past 7 billion years

Pritom Mozumdar, Michele Cappellari, Christopher D. Fassnacht et al. (+1 more)

Understanding how the internal kinematics of massive galaxies evolve is key to constraining the physical processes that drive their assembly. We investigate the evolution of rotational support in massive ($\log M_{\ast}/M_{\odot} \geq 10.6$) early-type galaxies (ETGs) over the past $\sim$7 Gyr. We use MUSE integral-field spectroscopic (IFS) data for 212 ETGs at intermediate redshift ($0.25 < z < 0.75$) from the MAGNUS sample. We compare their kinematics to a carefully matched local sample of 787 ETGs ($z \leq 0.05$) from the MaNGA survey. Using the specific stellar angular momentum proxy, $\lambda_R$, we quantify the balance between ordered rotation and random motions. We derive intrinsic $\lambda_R$ values by applying a uniform correction for seeing and point-spread function (PSF) effects to both samples. We find a significant evolutionary trend: the intermediate-redshift ETGs are systematically more rotationally supported than their local counterparts. The median PSF-corrected $\lambda_R$ for the MAGNUS sample is $0.48 \pm 0.05$, substantially higher than the median of $0.34 \pm 0.03$ for the matched MaNGA sample. This corresponds to a positive slope in the $\lambda_R-z$ relation of $\mathrm{d} \lambda_R / \mathrm{d} z = 0.3 \pm 0.04$ for the combined sample. The decline in rotational support is most pronounced for the most massive galaxies ($\log M_{\ast}/M_{\odot} > 11.3$). Our results provide robust evidence that massive ETGs have undergone significant kinematic evolution, losing angular momentum as they evolve towards the present day, consistent with theoretical models where processes such as dry mergers play a crucial role in shaping the dynamical state of galaxies.
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All authors Pritom Mozumdar, Michele Cappellari, Christopher D. Fassnacht, Tommaso Treu

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

Vacuum breakdown around a Kerr black hole surrounded by a magnetic field

C. Cherubini, R. Moradi, J. A. Rueda et al. (+1 more)

We present the invariant characterization of the region where vacuum breakdown into electron-positron ($e^+e^-$) pairs occurs due to an overcritical electric field, the dyadoregion, in the case of a Kerr black hole (BH) in the presence of an external, asymptotically uniform test magnetic field aligned with the BH rotation axis, using the Wald solution. We calculate the dyadoregion morphology, the electromagnetic energy available to the pairs, the pair-creation rate, the pair number density, the average energy per pair, and the pair energy density and pressure. These results provide initial conditions for simulating the subsequent dynamics of the pair-produced plasma and astrophysical applications in the context of high-energy transients involving BHs in strong electromagnetic fields.
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All authors C. Cherubini, R. Moradi, J. A. Rueda, R. Ruffini

Astrophysics of Galaxies

MAGNUS I: A MUSE-DEEP Sample of Early-type Galaxies at Intermediate Redshift

Pritom Mozumdar, Michele Cappellari, Christopher D. Fassnacht et al. (+1 more)

We present a sample of 213 early-type galaxies (ETGs) at redshifts $0.25 < z < 0.75$. We combine deep integral-field spectroscopy from the MUSE-DEEP survey with high-resolution HST imaging to study the structure, kinematics, and stellar populations of these galaxies. We measure spatially resolved stellar kinematics and use the specific angular momentum proxy, $\lambda_R$, to classify galaxies into fast and slow rotators. We find a slow rotator fraction consistent with local Universe samples, suggesting little evolution in the massive ETG population since $z \sim 1$. The kinematic and photometric axes of fast rotators are generally well-aligned, similar to their local counterparts. We find that global stellar population properties, such as age, metallicity, and mass-to-light ratio ($M_*/L$), correlate strongly with the central velocity dispersion ($\sigma_\mathrm{e}$), following trends established for local ETGs. Slow rotators are typically more massive, have higher $\sigma_\mathrm{e}$, and are more metal-rich than fast rotators. Our findings indicate that the fundamental structural, kinematic, and stellar population scaling relations of massive ETGs were already in place by $z \sim 0.75$, suggesting their evolutionary pathways have remained stable over the last $\sim 7$ Gyr.
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All authors Pritom Mozumdar, Michele Cappellari, Christopher D. Fassnacht, Tommaso Treu

Earth and Planetary Astrophysics

Wind-AE: A Fast, Open-source 1D Photoevaporation Code with Metal and Multi-frequency X-ray Capabilities

Madelyn Broome, Ruth Murray-Clay, John McCann et al. (+1 more)

Throughout their lives, short period exoplanets (<100 days) experience X-ray and extreme-UV (XUV) stellar irradiation that can heat and photoionize planets' upper atmospheres, driving transonic outflows. This photoevaporative mass loss plays a role in both evolution and observed demographics; however, mass loss rates are not currently directly observable and can only be inferred from models. To that end, we present an open-source fast 1D, XUV multi-frequency, multispecies, steady-state, hydrodynamic Parker Wind photoevaporation relaxation model based on Murray-Clay et al. (2009,arXiv:0811.0006). The model can move smoothly between high and low flux regimes and accepts custom multi-frequency stellar spectra. While the inclusion of high-energy X-rays increases mass loss rates ($\dot{M}$), metals decrease $\dot{M}$, and the net result for a typical hot Jupiter is a similar $\dot{M}$, but a hotter, faster, and more gradually ionized wind. We find that mulitfrequency photons (e.g., 13.6-2000eV) are absorbed over a broader range of heights in the atmosphere resulting in a wind-launch radius, $R_{XUV}$, that is of order 10 nanobars for all but the highest surface gravity planets. Grids of H/He solar metallicity atmospheres reveal that, for typical hot Jupiters like HD 209458b, $R_{XUV}$~1.1-1.8$R_P$ for low-fluxes, meaning that the energy-limited mass loss rate, $\dot{M}_{Elim}(R)$, computed at $R=R_P$ is a good approximation. However, for planets with low escape velocities, like many sub-Neptunes and super-Earths, $R_{XUV}$ can be >>$R_P$, making it necessary to use $\dot{M}_{Elim}(R=R_{XUV})$ to avoid significantly underestimating mass loss rates. For both high escape velocities and large incident fluxes, radiative cooling is significant and energy-limited mass loss overestimates $\dot{M}$.
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All authors Madelyn Broome, Ruth Murray-Clay, John McCann, James E Owen

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

Imperfect dark matter with higher derivatives

Mohammad Ali Gorji

We introduce a higher-derivative action for dark matter whose energy-momentum tensor describes an imperfect fluid with nonzero pressure, energy flux, and anisotropic stress. In the limit where the higher-derivative couplings are switched off, the energy-momentum tensor reduces to pressureless dust. A systematic derivation follows from extending the singular conformal transformation used in the mimetic dark matter scenario to include higher-derivative terms while the resulting action is general and does not rely on the mimetic framework. On a homogeneous cosmological background, the dynamics coincides with that of pressureless dust, while in the presence of inhomogeneities the higher-derivative terms generate nonzero acceleration and vorticity, making it possible to avoid the formation of caustic singularities even if the strong energy condition satisfies. In particular, within the mimetic realization these terms can resolve the usual caustic pathology of mimetic dark matter.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Constraining the gravitational-wave emission of core-collapse supernovae with ground-based detectors

Jingwang Diao and Xingjiang Zhu

A gravitational-wave background (GWB) arising from the superposition of numerous unresolved gravitational-wave signals has yet to be detected. Potential contributing sources to such a background include compact binary coalescences (CBCs) and core-collapse supernovae (CCSNe). In this work, we place upper limits on the gravitational-wave energy emitted by CCSNe using cross-correlation measurements made with Advanced LIGO and Advanced Virgo detectors during their third observing run. Specifically, we obtain a $95\%$ credibility upper limit of $0.01~ {M_\odot c^2}$ while accounting for the contribution from CBC sources to a GWB. This result improves on previous constraint obtained from initial LIGO data by approximately two orders of magnitude. We also explore the detection prospects of third-generation ground-based detectors such as the Einstein Telescope and Cosmic Explorer for both individual CCSNe events and the GWB. Our results show that single events are likely to be detected prior to the GWB.
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