Solar and Stellar Astrophysics
Angular momentum transport in the convection zone of a 3D MHD simulation of a rapidly rotating core-collapse progenitor
Ryota Shimada, Lucy O. McNeill, Vishnu Varma et al. (+3 more)
Rotation and
magnetic fields in the cores of evolved massive
stars in their final phase are thought to play an important role in the subsequent
supernova explosion and the formation of a compact object, especially in hyperenergetic explosions. However, the interplay between rotation,
magnetic fields, and convection up to the final collapse is a nonlinear, multidimensional effect that is difficult to capture with standard one-dimensional (1D)
stellar evolution models. We quantify the
magnetic angular momentum (AM) transport in the convective oxygen burning shell in a three-dimensional (3D) rotating core-collapse progenitor model. We find that the radial direction of
magnetic AM transport is directly related to the Rossby number of the convective oxygen shell. We also analyze the
magnetic energy, which sets the amplitude of the
magnetic AM flux. The
magnetic energy is determined both by rotation and the
nuclear energy generation rate analogously to low-mass
stars like the Sun. Based on these results, we construct a 1D model of
magnetic AM transport in the convection zone for the first time in terms of properties of a given
stellar evolution model. This model successfully reproduces the AM transport in the 3D model when the convective dynamo is in a quasi-steady state. Notably, our model for radial AM transport is the first to account for inward AM flux. This may result in interesting differences compared to the conventional treatment of
magnetic AM transport in
stellar evolution models, which assume AM is transported outward by a purely diffusive process.
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All authors Ryota Shimada, Lucy O. McNeill, Vishnu Varma, Keiichi Maeda, Takaaki Yokoyama, Bernhard Müller
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Evaluation of QED cross sections in strong magnetic fields
Olavi Kiuru
Quantum electrodynamics (QED) becomes nonlinear when the
magnetic field strength surpasses the critical Schwinger limit $B_Q \approx 4.41\cdot 10^{13}$ G. This limit is surpassed, for example, in the magnetospheres of a specific class of
neutron stars known as magnetars, which has important consequences for magnetospheric
plasma dynamics due to modifications in scattering cross sections. Using a formalism previously applied to the study of
magnetic catalysis, I calculate the cross sections of all tree-level 1-to-2, 2-to-1, and 2-to-2 particle QED scattering processes that do not include a
photon propagator. The calculations are done in a strong background
magnetic field and the results are implemented into an open-source Python package. This article focuses on presenting the formalism and computational techniques required for the calculations, while the impact of the results on, e.g., magnetospheric
plasma dynamics is discussed in a companion letter (Kiuru et al. 2026).
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Solar and Stellar Astrophysics
Formation and Evolution of [Wolf-Rayet] Planetary Nebulae through a Late Thermal Pulse
J.B. Rodríguez-González, R. Orozco-Duarte, J. A. Toalá et al. (+5 more)
We present the first radiation-hydrodynamical simulations of the formation of a born-again planetary nebula (PN) triggered by a late thermal pulse (LTP). The 2D radiation-hydrodynamic simulations, performed with the pluto code, have been consistently coupled to
stellar evolution calculations using the Modules for Experiments in
Stellar Astrophysics (mesa) code. Very particularly the
stellar evolution model uses (i) updated opacity tables for H-deficient, C-rich mixtures during the LTP, and (ii) a mass-loss prescription tailored for H-deficient [Wolf-Rayet]([WR])-type winds during the post-LTP phase. Our
stellar model reproduces the nearly complete depletion of H expected after an LTP event, while matching the observed abundances and spectral types of iconic [WR]-type central
stars of PNe. The simulations show for the first time that the H-deficient LTP ejecta forms a transient double-shell structure which, after $\sim$1000 yr, becomes fully mixed with the H-rich PN. The ejecta mass ($\sim3.4\times10^{-4}$~M$_\odot$) is too small to leave a lasting imprint on the nebular abundances, predicting H-rich PNe around [WR] central
stars. The injection of LTP material into the hot bubble drives
turbulence, clump formation, and enhanced mixing, providing an explanation to the larger expansion velocities and larger turbulent nebular structures of PNe with [WR] central
stars compared to those with H-rich central
stars. These results provide robust support for the born-again scenario as the origin of H-deficient [WR] central
stars within H-rich PNe.
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All authors J.B. Rodríguez-González, R. Orozco-Duarte, J. A. Toalá, M. M. Miller Bertolami, H. Todt, M.A. Guerrero, L. Conmy, R. Kuiper
Cosmology and Nongalactic Astrophysics
Extracting Cosmological Information from Lightcone Data: A Comparison of CNNs and Summary-Statistic-Based Approaches
Min Zhiwei, Xiao Xu, Jiang Zhujun et al. (+9 more)
Lightcone observations are the natural data format of
galaxy surveys, but their evolving geometry breaks the translational
symmetry assumed by standard convolutional neural networks (CNNs). In particular, applying CNNs to 3D gridded lightcone data implicitly treats the line-of-sight direction as translationally invariant, despite encoding
cosmic time
evolution. We propose a simple alternative (CNN+2D) that divides the lightcone into
redshift slices, projects each onto a HEALPix sphere, and analyzes them with a 2D CNN. Using AbacusSummit
halo lightcone mocks ($0.3<z<0.8$, $40^\circ\times40^\circ$), we compare this approach with fully connected networks (FC) applied to different summary statistics, including spherical harmonic coefficients ($a_{\ell m}$), wavelet scattering transform (WST) coefficients, and the angular two-point correlation function (2PCF), along with standard 2PCF likelihood and Fisher forecasts. We find that multiple statistics beyond CNNs can achieve competitive performance: FC networks combined with $a_{\ell m}$ and especially WST significantly outperform 2PCF-based methods, with FC+WST yielding the best overall parameter constraints across cosmologies. Meanwhile, for a fiducial cosmology with multiple realizations, the CNN+2D approach achieves the smallest statistical uncertainties. These results demonstrate that both learned features and carefully constructed summary statistics can effectively extract cosmological information from lightcone data, providing flexible and robust analysis strategies for upcoming surveys such as DESI, Euclid, and CSST.
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All authors Min Zhiwei, Xiao Xu, Jiang Zhujun, Xiao Liang, Yin Fenfen, Ding Jiacheng, Miao Haitao, Chen Shupei, Lin Qiufan, Wang yang, Zhang Le, Li XiaoDong
Instrumentation and Methods for Astrophysics
Conditional Neural Bayes Ratio Estimation for Experimental Design Optimisation
S. A. K. Leeney, T. Gessey-Jones, W. J. Handley et al. (+3 more)
For frontier experiments operating at the edge of detectability, instrument design directly determines the probability of discovery. We introduce Conditional Neural Bayes Ratio Estimation (cNBRE), which extends neural Bayes ratio estimation by conditioning on design parameters, enabling a single trained network to estimate Bayes factors across a continuous design space. Applied to 21-cm
radio cosmology with simulations representative of the REACH experiment, the amortised nature of cNBRE enables systematic design space exploration that would be intractable with traditional point-wise methods, while recovering established physical relationships. The analysis demonstrates a ~20 percentage point variation in detection probability with
antenna orientation for a single night of observation, a design decision that would be trivial to implement if determined prior to
antenna construction. This framework enables efficient, globally-informed experimental design optimisation for a wide range of scientific applications.
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All authors S. A. K. Leeney, T. Gessey-Jones, W. J. Handley, E. de Lera Acedo, H. T. J. Bevins, J. L. Tutt
Earth and Planetary Astrophysics
The atmosphere of K2-18 b: The role of hazes, clouds and photoelectrons
P. Lavvas, R. Liu, G. Tinetti et al. (+3 more)
The atmospheric characterisation of temperate
exoplanets is becoming accessible with JWST, providing a critical connection between
Solar System
planets and the more commonly observed hot-Jupiters. K2-18 b, a temperate sub-Neptune orbiting an M
dwarf, has emerged as a
benchmark case following extensive JWST observations and ongoing debate regarding its atmospheric composition. We investigate K2-18 b using a self-consistent forward model to constrain its
metallicity, composition, and thermal structure, with particular emphasis on the role of disequilibrium chemistry, photochemical hazes and clouds. For the first time in this context, we also assess the impact of photoelectrons on the atmospheric chemistry of an
exoplanet. We explore a wide range of
metallicities and intrinsic temperatures, evaluate haze and cloud formation, and compare the resulting transmission spectra with available JWST observations from multiple independent pipelines. We find that a high
metallicity (200-400xsolar) H2-rich atmosphere consistently reproduces the observed transit spectra, independent of the data reduction pipeline used. The atmospheric composition is strongly shaped by disequilibrium chemistry, with CH4 dominating the spectrum alongside contributions from CO2 and OCS, and a potential contribution from C2H4 at mid-infrared wavelengths. Photoelectrons enhance the production of several disequilibrium species, particularly nitrogen-bearing molecules. Photochemical hazes play a key role in shaping the thermal structure, producing a temperature minimum near the 10-100 mbar range that enables efficient H2O condensation, suppressing its gaseous abundance. Under sufficiently strong haze cooling, NH4SH condensation provides a natural explanation for the apparent absence of NH3 in the observed spectra. No additional molecular species beyond those considered here are required to reproduce the observed spectra.
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All authors P. Lavvas, R. Liu, G. Tinetti, S. Paraskevaidou, P. Drossart, A. Coustenis
High Energy Astrophysical Phenomena
NuSTAR's Intentional Stray Light Observation of Scorpious X-1
S. Li, R. M. Ludlam, M. Sudha et al. (+8 more)
We present the first spectral analysis of Scorpius X-1 (Sco X-1) using intentional stray light (SL) observations taken by NuSTAR. Unlike focused observations that have high telemetry load when observing bright sources, intentional SL observations can help reduce the telemetry and reduce the effect of dead time, thereby maximizing the on-source exposure time; all of which are critical for extremely bright sources that exhibit short timescale variability like Sco X-1. The intentional SL observation of Sco X-1, taken in 2023, captured the source primarily in the flaring branch (FB) of the Z track. We performed spectral modeling of the continuum and reprocessed emission. A combination of thermal and Comptonization components (modeled with thcomp) provided a robust fit to the continuum. We test both scenarios for Comptonized emitting regions arising from the
accretion disk and close to the
neutron star, which provides comparable fit statistics. Reflection was modeled with the relxillNS model, enabling measurements of disk inclination consistent with prior
radio and IXPE studies and comparison of inner disk radius to the emission radii of the thermal components. Overall, the results from the intentional SL data provide comparable results to literature on the focused NuSTAR data of Sco X-1 in the FB or taken contemporaneously. The success of this observation demonstrates the capability of SL data to yield high-quality spectral constraints comparable to focused observations, offering a powerful avenue for studying bright X-ray binaries with NuSTAR.
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All authors S. Li, R. M. Ludlam, M. Sudha, M. C. Brumback, D. J. K. Buisson, B. M. Coughenour, A. Di Marco, B. W. Grefenstette, F. La Monaca, G. Mastroserio, S. Rossland
High Energy Astrophysical Phenomena
Relativistic Tidal Disruption in Black Hole and Wormhole Backgrounds
Pritam Banerjee, Kowsona Chakraborty, Niles Mondal et al. (+1 more)
Black holes (BHs) and wormholes (WHs) are characterized by distinct spacetime geometries, whose differences become pronounced close to the central objects. A useful way to probe such differences is via the dynamics of
stellar tidal disruption events in the regime of strong
gravity. Here, using a general relativistic smoothed particle hydrodynamics code inspired from an
algorithm developed by Liptai and Price, we perform a suite of numerical simulations of
solar mass polytropic
stars in the background of supermassive Schwarzschild BHs and similar mass exponential WHs. Important differences between the two geometries near the BH event horizon or the WH throat is provided by the distinct outcomes of such events. For a given impact parameter, BH backgrounds lead to greater
tidal stripping compared to WHs ones and further, the critical impact parameter, beyond which the
star undergoes full
tidal disruption is higher for WH backgrounds compared to BHs. We further study the differences in observable peak fallback rates in the two backgrounds. We also provide a quantitative explanation for the tendency of
stars in partial
tidal disruptions to retain larger cores around more massive centers, by computing
tidal stresses in a
Fermi normal coordinate system and introducing an appropriate measure of
stellar compactness. Finally, we suggest a way to observationally distinguish BH and WH backgrounds, based on the properties of different observables.
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All authors Pritam Banerjee, Kowsona Chakraborty, Niles Mondal, Tapobrata Sarkar
Instrumentation and Methods for Astrophysics
Tomo-V – a New Tool for Doppler Tomography
P.V. Kaygorodov
In this paper, a new tool for Doppler
tomography, Tomo-V (https://tomo-v.inasan.ru) that is developed based on the algebraic reconstruction technique (ART) has been presented. Previously, the ART method has not been widely used in
tomography, as its direct implementation was computationally complex. The author has developed a fast version of this
algorithm, which allowed it to be implemented within a web application that runs at acceptable speed in a browser on a personal computer. This method can be used to obtain sharp tomographic images from blurred profiles. Furthermore, the method has demonstrated excellent results in reconstructing images from noisy data, from a small number of profiles, and from profiles contaminated by absorption lines and emission from the expanding envelope. Tomo-V also includes tools for analyzing the resulting tomograms, allowing the position of
accretion disks and Roche lobes to be displayed on the tomogram, as well as back-projecting the tomographic image onto flow elements in spatial coordinates. The paper is partially based on a report presented at the Modern
Stellar Astronomy 2025 conference.
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Instrumentation and Methods for Astrophysics
Quadratic shift-and-stack for Ground-Based Optical Detection of Faint Cislunar Objects
Qi Li, Yuhui Zhao, Chengxing Zhai et al. (+2 more)
Detecting faint objects in cislunar space using ground-based optical
telescopes is difficult because of their low brightness, strong lunar background, and complex, nonlinear apparent motion. Traditional shift-and-stack techniques based on linear motion assumption suffer signal trailing loss due to significant nonlinear motion during long integrations, thus producing a degraded signal-to-noise ratio (SNR). In this paper, we first derive a theoretical criterion based on the point spread function to determine the maximum applicable integration time for linear-motion stacking. We then propose a quadratic shift-and-stack (QSS) method to correct for the first-order nonlinear motion, namely the angular acceleration of cislunar targets. Simulations of typical cislunar orbits verify this theoretical criterion and show that the QSS method significantly improves SNR from stacking and can enhance the detection limit by up to 1
stellar magnitude compared with the linear-motion stacking method. Furthermore, tests using observational data of the cislunar object Tiandu-1 confirm that while linear stacking degrades after a 29-minute integration due to trajectory
curvature, the QSS method achieves continuous SNR improvement over a 46-minute integration, outperforming the peak SNR of the linear method by 31%.
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All authors Qi Li, Yuhui Zhao, Chengxing Zhai, Yang Wang, Yi Han
High Energy Astrophysical Phenomena
The Gravitational-Wave Power Gap in Core-Collapse Supernovae: Insights from 60 Axisymmetric Simulations
Haakon Andresen, Xingzao Li, Aurore Betranhandy et al. (+3 more)
We analyse the gravitational-wave emission from 60 two-dimensional core-collapse
supernova simulations. The models cover a range of progenitors and equations of state. We focus on the narrow frequency interval in the gravitational-wave spectrum where the emitted power is strongly suppressed (the power gap) and how its central frequency relates to the physical properties of the simulations. We find that the power-gap frequency exhibits strong and systematic correlations with the properties of the inner core of the forming
neutron star, for example the sound speed, suggesting that the gap encodes information about the behaviour of matter at extreme densities. We further examine how well several mechanisms proposed in the literature account for the presence and
evolution of the gap in our simulations. Finally, we explore a scenario in which the gap arises from destructive interference between a narrow oscillation mode and a broadband background signal, demonstrating that such an interaction can produce a sharp minimum in the emitted gravitational-wave power.
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All authors Haakon Andresen, Xingzao Li, Aurore Betranhandy, Evan P. O'Connor, Shuai Zha, Sean M. Couch
Astrophysics of Galaxies
Population III star formation in an X-ray background: V. Environmental dependence and halo occupation probability
Jongwon Park and Massimo Ricotti
An X-ray background in the early Universe enhances molecular hydrogen formation, the main coolant of
primordial gas, thereby lowering the threshold for Pop III
star formation. Continuing our series on X-ray impacts on Pop III
star formation, we investigate how a soft X-ray background promotes Pop III
star formation using cosmological zoom-in simulations of ten
cosmic volumes spanning a range of
halo number densities. Each volume is irradiated by the Lyman-Warner (LW) H$_{2}$ dissociating background and a weak (J$_{21} \sim 10^{-5}$), soft ($E \sim 0.2-2.0$ keV) X-ray background produced by pair-instability SNe (PISNe) from Pop III
stars and calculated self-consistently as described in a companion paper. We also compare the same simulations with and without X-rays to isolate the X-ray effect. The background promotes Pop III
star formation in two ways: (1) by reducing the mean host
halo mass by a factor of $\sim 2-3$, and (2) by enabling Pop III
star formation in
haloes that would otherwise remain sterile, thereby increasing the
halo occupation fraction. The resulting gain in Pop III number density is largest in underdense regions (a factor of $\approx 3$ on average, reaching up to 7). In the most extreme case, Pop II
stars form only in the presence of X-rays and the gas-phase
metallicity rises by an order of magnitude, suggesting that
dwarf galaxies in underdense regions may be significantly influenced by an early X-ray background. We also provide fitting functions for the
halo occupation probability of Pop III
stars as a function of
redshift for both X-ray and LW-only simulations, which can serve as inputs for semi-analytic models.
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Astrophysics of Galaxies
Population III star formation in an X-ray background: IV. On-the-fly calculation of radiation backgrounds and their impact on the intergalactic medium
Jongwon Park and Massimo Ricotti
In this paper, part of a series on the effects of X-ray sources in promoting Population III (Pop III)
star formation, we investigate the ionisation and heating of the intergalactic medium (IGM) and the consequent enhancement of molecular hydrogen (H$_{2}$) and Pop III formation using cosmological zoom-in simulations. We adopt a minimal X-ray feedback model in which X-rays originate solely from Pop III
supernovae, and compute the global X-ray and Lyman-Werner (LW) radiation backgrounds on-the-fly during the simulation of a mean-density region of the Universe. This approach self-consistently captures the feedback loop between Pop III
stars and the radiation backgrounds they produce. Pop III
supernovae generate a weak X-ray background (J$_{\mathrm{X,21}} \sim 10^{-5}$) and a moderate LW background (J$_{\mathrm{LW,21}} \sim 10^{-1}$); the latter intensifies below $z \approx 12$ (J$_{\mathrm{LW,21}} \sim 10^{1}-10^{2}$) with the onset of Pop II
star formation. Applying these backgrounds to regions of varying mean density produces a net positive X-ray feedback that increases the Pop III number density, with stronger enhancement in underdense regions. The positive feedback is more pronounced when the X-ray background is computed on-the-fly rather than by post-processing, demonstrating the importance of the feedback loop. The X-ray background also raises the Thomson scattering optical depth at high
redshift, while the total optical depth remains consistent with Planck 2018 constraints. Because our model includes only Pop III
supernovae as X-ray sources, it represents the most conservative scenario; stronger X-ray feedback is expected when additional sources are included, as will be explored in future work.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Circular orbits in spherically symmetric spacetimes and BSW effect with nonzero force
Hryhorii Ovcharenko and O. B. Zaslavskii
We consider circular particle motion under the action of an unspecified force in a static spherically symmetric spacetime. We derive the machinery that allows one to find the force acting on a circular particle and deduce whether its position is stable or not. This also allows one to extend the definition of ISCO to the case of a non-zero external force. By conducting the near-horizon expansion, we obtain that for any non-extremal black holes, the acceleration for extremal ones is finite, and for ultraextremal (multiple) horizons it tends to zero. Applying the derived machinery to the case of the Schwarzschild metric assuming that a force is constant, we scrutiny how the number of orbits for a given force depends on its value. In particular, if a force is big enough, an additional branch of solutions appears that was absent in the case of geodesic motion. Then, for various circular orbits, we numerically investigate their stability. A similar problem is solved for the Reissner-Nordstrom (RN) metric and uncharged particles. It appears that for the near-extremal and extremal RN black holes, there exist near-horizon circle trajectories (in contrast to the nonextremal case). For the ISCO, the dependence of the orbit radius on $\kappa$ (the surface
gravity) is similar to that in the case of neutral particles moving in the background of rotating black holes. In addition, two scenarios of high-energy particle collisions near such orbits are considered, and it is found that dependence on $\kappa$ is also similar to that for rotating black holes.
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High Energy Astrophysical Phenomena
Particle Acceleration in Cassiopeia A Revealed by Broadband High-Energy Spectrum
Bo-Tao Li, Wei Wang and Zhuo Li
Recently, the GeV–sub-PeV spectrum of
supernova remnant (SNR) Cassiopeia A (Cas A), one of the youngest and most well-studied SNRs in our
Galaxy, has been updated by observations of
Fermi-LAT and LHAASO. We revisit Cas A with our previous shell-plus-jet asymmetric model and investigate its particle acceleration ability. The broadband fitting results suggest that the double-peaked gamma-ray spectrum can be well attributed to
proton-
proton (PP) collisions and inverse Compton scattering within the SNR shell, while the synchrotron emission from a jet component with velocity of $\sim0.1c$ can account for the hard X-ray emission up to 220 keV. Furthermore, the PP collisions in the jet can produce a sub-PeV emission, but constrained by the LHAASO-KM2A limit to a flux below $\sim 1\times10^{-14}\rm erg/(cm^2s)$ at 100 TeV. The energy of accelerated
protons in the jet of Cas A could be up to $5\times10^{47}$ erg, which, assuming that the PeV
cosmic ray distribution is clumpy in the
Galaxy with the clump size comparable to the thickness of the
Galactic plane, derives a
proton flux consistent with the observed one at 1 PeV, implying that the Cas A-like SNRs can still be PeVatrons in the
Galaxy. It is encouraging for LHAASO and future
telescopes to detect or constrain Cas A spectrum above 100-TeV more precisely.
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Solar and Stellar Astrophysics
Energy Transport and Heating by Non-Thermal Electrons in a Turbulent Solar Flare Environment
A. Gordon Emslie and Eduard P. Kontar
The impulsive phase of a
solar flare is known to generate strong
turbulence and to transfer
magnetic energy into accelerated electrons. Recognizing the importance of angular
diffusion on the dynamics of the accelerated electrons, we extend previous treatments by deriving analytic solutions for the electron flux and associated energy deposition in two regimes: scattering dominated by inelastic Coulomb collisions and scattering dominated by elastic interactions with turbulent scattering centers. We show that the
turbulence-dominated scattering term strongly reshapes the spatial distribution of the
plasma heating: compared to the traditional collisional thick-target approach, turbulent scattering could lead to an order-of-magnitude increase in coronal heating and an even greater suppression of chromospheric heating. Scattering also acts to reduce the anisotropy of the electron distribution and so reduces the net current associated with the nonthermal electrons. The return-current Ohmic heating is accordingly reduced to a level that renders it negligible compared to direct collisional heating. The results have significant implications for models of atmospheric response to impulsive phase energy release, in particular chromospheric evaporation,
flare-driven coronal heating, the formation of loop-top hard X-ray sources, and the longstanding discrepancy between modeled and observed soft X-ray line profiles.
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High Energy Astrophysical Phenomena
Probing anisotropic particle acceleration and limb-brightening in Centaurus A's jet
Felix Glaser, Christian M. Fromm, Luca Ricci et al. (+4 more)
Relativistic jets are among the most fascinating objects in the Universe, and recent high-resolution Very Long Baseline Interferometric (VLBI) observations, including the Global mm-VLBI Array and the Event Horizon
Telescope (EHT), are able to resolve their structure close to their launching site. These observations reveal strongly limb-brightened jet structures for Centaurus A (Cen A), M 87 and 3C 84. Thus, the question arises which physical mechanism can generate the limb-brightened structure, and if this structure is common for jets from low-luminosity active
galactic nuclei (LLAGN) seen under large viewing angles. Therefore, as a pilot study, we aim to model the EHT observations of Cen A. We performed a 3D two-temperature general-relativistic magnetohydrodynamic (GRMHD) simulation of an accreting supermassive black hole (SMBH) and jet launching to study the
plasma dynamics and computed the connected emission via general relativistic radiative transfer (GRRT) calculations considering possible anisotropies in the distribution of the radiating particles. In order to adjust our simulations to the EHT observations of Cen A, we carried out a
Bayesian fitting in the
Fourier plane. We find that GRMHD simulations of magnetically arrested disks (MADs) combined with anisotropically emitting particle distributions along the direction of the
magnetic field, parametrized by a value $\eta=0.07$, are able to mimic the recent EHT observations of Cen A. In addition, we extracted a black hole mass of $M_\mathrm{BH} = 6\times10^7 M_\odot$ and a viewing angle of $\vartheta=72\deg$. Our obtained model can reproduce key features of the EHT and Atacama Large Millimeter/submillimeter Array (ALMA) observations in total and polarized emission. Finally, we predict that the black hole shadow in Cen A will be observable at a frequency of $\sim$ 3 THz.
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All authors Felix Glaser, Christian M. Fromm, Luca Ricci, Yosuke Mizuno, Matthias Kadler, Karl Mannheim, Michael Janssen
High Energy Astrophysical Phenomena
An energetic dirty fireball detected in soft X-rays
C.-Y. Dai, J. Quirola-Vásquez, Y.-H. Wang et al. (+76 more)
The collapse of massive
stars drives explosions that power relativistic fireballs. If only a small amount of matter is entrained, such clean fireballs can expand with Lorentz factors $\Gamma> 100$, accounting for gamma-ray bursts (GRBs). It has been hypothesized that energetic explosions with more
baryon contamination, dubbed “dirty fireballs”, may exist in nature, but they have not been observed. Here we report the observation of an extragalactic fast X-ray transient, EP241113a, detected by Einstein Probe. Compared to GRBs, it has a similar isotropic energy of $1.4\times 10^{51}$ erg, but significantly lower spectral peak energy. Theoretical modeling of its early X-ray afterglow suggests a relativistic jet with a low Lorentz factor of $\Gamma \sim 20$ aligned close to the line-of-sight, signifying the prototype of a dirty fireball.
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All authors C.-Y. Dai, J. Quirola-Vásquez, Y.-H. Wang, H.-L. Li, J. Yang, X.-L. Chen, A.-L. Wang, H. Sun, X.-Y. Wang, B. Zhang, P. G. Jonker, Y. Liu, W. Yuan, D. Xu, Z.-G. Dai, M. E. Ravasio, L. Piro, P. O'Brien, D. Stern, H.-M. Zhang, Y.-P. Yang, T. An, Y.-L. Qiu, L.-P. Xin, W.-X. Li, R.-Y. Liu, X.-F. Wu, C.-Y. Wang, D.-M. Wei, Y.-F. Huang, F. E. Bauer, W.-H. Lei, B.-B. Zhang, N.-C. Sun, H. Gao, V. S. Dhillon, J. An, C.-H. Bai, A. Martin-Carrillo, H.-Q. Cheng, J. A. Chacon Chavez, Y. Chen, G.-W. Du, J. N. D. van Dalen, A. Esamdin, Y.-Z. Fan, X. Gao, F. Harrison, J.-W. Hu, M.-Q. Huang, S.-M. Jia, A. J. Levan, C.-K. Li, D.-Y. Li, E.-W. Liang, S. Littlefair, X.-W. Liu, Z.-Y. Liu, Z.-X. Ling, D. B. Malesani, H.-W. Pan, A. Rodriguez, A. Rossi, D. Mata Sánchez, J. Sánchez-Sierras, X.-J. Sun, M. A. P. Torres, A. P. C. van Hoof, X.-F. Wang, Q.-Y. Wu, X.-P. Xu, Y.-F. Xu, Y.-W. Yu, C. Zhang, M.-H. Zhang, S.-N. Zhang, Y. Zhang, Y.-H. Zhang, Z.-P. Zhu
Astrophysics of Galaxies
Turning JWST/MIRI backgrounds into a survey of diffuse molecular hydrogen
E. Nigou, B. Godard, P. Guillard et al. (+3 more)
Context. A statistically significant sampling of H2 rotational excitation in the diffuse interstellar medium (ISM) is essential to identifying its excitation mechanisms and assessing the importance of H2 in the cooling of the gas and the regulation of thermal pressure. Aims. To complement the statistics provided by ancillary
telescopes, we conducted a search for pure rotational H2 emission lines in all publicly available background observations obtained with the Medium Resolution Spectrometer (MRS) aboard the JWST. Methods. The sample consists of 276 background observations acquired over the past three years. Departing from the standard pipeline, each uncalibrated MRS background file was reprocessed, enabling the analysis of H2 pure rotational emission. Lines of sight likely associated with
star-forming complexes were excluded to focus on emission from the diffuse ISM. The results were compared with FUSE absorption data and were analyzed in relation to the column densities of H and H2 and to
dust emission derived from HI4PI, Planck, and WISE data. Results. This analysis reveals widespread H2 emission throughout the
Galaxy. We report the first detections of the pure rotational S(4), S(5), and S(7) lines in the diffuse ISM. The S(1) line is detected along 84 lines of sight, corresponding to a detection rate of 41%. Its integrated intensity decreases steeply with
Galactic latitude, spanning nearly two orders of magnitude, in remarkable agreement with absorption measurements. The T\_34 and T\_35 excitation temperatures vary between 200 and $\sim$1000 K, are correlated with each other, and are anticorrelated with the column density of H2 , as expected from ancillary data. All lines of sight in the sample have undergone the H-H2 transition, at N\_H ___ 10 +20 cm -2 , and are partly molecular, with f\_H2 ___ 0.1. Under these conditions, the cooling rate associated with the S(1) line, expressed per hydrogen atom, is found to be remarkably constant, with a characteristic value of $\sim$4x10 -27 erg s-1 H-1. Conclusions. This study demonstrates that the high sensitivity of the JWST enables measurements that both strengthen and complement those from absorption studies. Observations collected over just a fraction of JWST's lifetime have already yielded detections along dozens of lines of sight, significantly expanding the statistical sample of H2 rotational excitation in the diffuse ISM.
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All authors E. Nigou, B. Godard, P. Guillard, G. Pineau Des Forêts, M A Miville-Deschênes, P. Lesaffre
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Neutron star structure and nuclear matter properties from a general Walecka-type model with Bayesian analysis
Yao Ma and Jia-Ying Xiong
We establish a
Bayesian analysis framework with a general Walecka-type relativistic mean-field model to study dense
nuclear matter under constraints from
nuclear matter properties and
neutron star observations. With experimental and observational data well described, we find that pure hadronic descriptions can generate a peak structure in sound velocity by $\omega$, $\rho$, $\sigma$, and $a_0$
meson mixing, which is crucial for describing both medium and massive
neutron stars. As the peak structure is frequently interpreted as a signature of phase transitions, our findings provide a new perspective on the microscopic origin of the sound velocity peak just with pure hadronic matter.
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Earth and Planetary Astrophysics
The role of inner disk edges in shaping ultra-short-period planet systems around late M dwarfs
S. N. Brandenberger, M. Sanchez, N. Van der Marel et al. (+2 more)
Close-in rocky
planets are the most common type of
exoplanets around late M
dwarfs, ranging from more temperate worlds to highly irradiated lava
planets with molten surfaces, and many theoretical studies have attempted to explain their formation. However, the origin of rocky
planets with orbital periods shorter than one day, known as ultra-short-period (USP)
planets, remains uncertain. We aim to investigate whether the formation and survival of USP
planets is connected to the location of the inner edge of the protoplanetary disk, considering different disk edge prescriptions. We use N-body simulations that include
planet-disk interactions,
star-
planet tidal interactions, and relativistic corrections, applied to a sample of lunar-mass planetary seeds growing via pebble
accretion in a low-viscosity disk ($\alpha_t = 10^{-4}$). The inner edge of the disk is modeled in three ways: as a fixed close-in edge, as an outward-evolving edge set by the magnetospheric truncation radius, and as an inward-evolving edge defined by the corotation radius. USP
planet formation appears to be tightly controlled by the location of the disk's inner edge. Our simulations show that only the close-in-fixed-edge Scenario and the inward-evolving-edge Scenario are capable of producing USP
planets, as
planets tend to follow the movement of the disk's inner edge. This suggests that USP
planet formation is favored when the inner edge remains close to the corotation radius of a rapidly rotating
star.
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All authors S. N. Brandenberger, M. Sanchez, N. Van der Marel, A. A. Vidotto, Y. Miguel
Astrophysics of Galaxies
The evolution of the sizes and angular momentum content of galaxies in the COLIBRE simulations
Aaron D. Ludlow, Katy L. Proctor, Joop Schaye et al. (+12 more)
We analyse the sizes and specific angular momentum content of
galaxies in the Colibre cosmological hydrodynamical simulations spanning two orders of magnitude in mass resolution. We compare the predicted size-mass and angular momentum-mass relations to a broad range of observational measurements spanning
redshifts $z=0$ to $4$. At $z=0$, Colibre reproduces observed size-mass relations over the sampled mass range $10^8 \lesssim M_\star/{\rm M_\odot}\lesssim 10^{11.5}$, and for multiple size definitions, including two- and three-dimensional
stellar half-mass radii, half-light radii across several wavelengths, as well as alternative measures such as baryonic half-mass radii and characteristic radii defined by
stellar surface density thresholds. The simulations also recover the observed segregation of
galaxies in the size-mass plane by morphological type and
star formation rate, and reproduce the distinct, approximately parallel sequences followed by
star-forming discs and quenched spheroids in the
stellar specific angular momentum-mass plane. The angular momentum content of
star-forming Colibre
galaxies matches that of observed systems out to $z\approx 1.5$. At higher
redshifts, massive
galaxies ($ 10^{9.5}\lesssim M_\star/{\rm M_\odot}\lesssim 10^{11}$) in the simulations are somewhat smaller than observed, and the separation between
star-forming and passive populations in the size-mass plane is reduced relative to observations, while at lower masses the agreement remains good. This apparent discrepancy may reflect the effects of
dust attenuation, which is neglected in our analysis and may preferentially obscure the central regions of observed systems. Overall, our findings highlight the close connection between
galaxy size, angular momentum, and morphology over
cosmic time.
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All authors Aaron D. Ludlow, Katy L. Proctor, Joop Schaye, Filip Huško, Victor J. Forouhar Moreno, Danail Obreschkow, Evgenii Chaikin, Matthieu Schaller, Sylvia Ploeckinger, Alejandro Benítez-Llambay, Kyle A. Oman, Robert J. McGibbon, James W. Trayford, Carlos S. Frenk, Alexander J. Richings
High Energy Astrophysical Phenomena
Challenges in Binary Pulsar Timing Detection of Dark Matter Subhalos
Zheng-Long Wang, Zi-Qing Xia, Yue-Lin Sming Tsai et al. (+1 more)
Recently, binary
pulsar timing has been proposed as a viable probe of dark matter subhalos with masses of $\sim 10^7\,M_{\odot}$ in the
solar neighborhood. We present a comprehensive analytical framework that incorporates the subhalo mass function, projection effects of line-of-sight acceleration, and the spatiotemporal
geometric requirements for joint detection by binary systems, enabling a quantitative evaluation of the detectability of nearby subhalos. Applying this framework to the current binary
pulsar sample, we find a probability $\leq 1.7 \times 10^{-4}$ of detecting at least one subhalo within the effective volume. An independent timing residual analysis shows no statistically significant excess in line-of-sight accelerations beyond predictions from data-driven
Galactic gravitational potential models. These results place stringent constraints on detecting $<10^8~M_{\odot}$ dark matter subhalos with existing
pulsar timing data, aligning with the theoretical expectation that such subhalos have a low survival probability in the
solar neighborhood. A low detection prospect still holds even for future Square Kilometre Array observations.
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All authors Zheng-Long Wang, Zi-Qing Xia, Yue-Lin Sming Tsai, Yi-Zhong Fan
Astrophysics of Galaxies
ROLLIN': Rotating globular cluster simulations. I. The kinematic evolution of realistic direct N-body models
P. Bianchini, A. L. Varri, A. Askar et al. (+2 more)
Internal rotation has emerged as a fundamental feature of globular clusters (GCs), yet its origin and long-term
evolution remain poorly understood. We explore the
evolution of rotating GCs over a Hubble time under the combined influence of two-body relaxation,
tidal field, and
stellar evolution. We introduce the ROLLIN' simulations, a suite of 25 N-body models characterized by a realistic number of
stars from 250k to 1.5M, ran with the direct N-body code NBODY6++GPU and evolved for 14 Gyr. With present-day masses of 5 x 10^4 - 5x10^5 M_sun, the models cover the parameter space of low-density MW GCs. Our analysis reveals that rapidly rotating GCs experience earlier and more pronounced core collapse, efficiently segregating massive objects and remnants in their centers within the first few 100 Myr. In the long-term, internal rotation declines and a correlation emerges between rotation and GC mass, in agreement with observations. The primary driver of this
evolution is mass loss, capturing both internal (
stellar evolution, evaporation) and external processes (
tidal stripping). The velocity anisotropy also evolves in response to mass loss: GCs initially near isotropy develop radial anisotropy, peaking around 40% mass loss, before progressing toward isotropy or tangentiality. The GC orbital history also plays a role, as retrograde rotators retain rotation more effectively than prograde rotators. Finally, we quantify the long-term changes of GCs after 12 Gyr: (1) The surface density decreases by up to 2 orders of magnitude. (2) The half-mass radius increases by a factor of 3-5. (3) The rotation decreases by a factor >5 for GCs that have lost >50% of their mass. The ROLLIN' simulations demonstrate that angular momentum is crucial to understand the origin,
evolution, and survival of GCs. These models provide a
benchmark for interpreting GC observations in the local and high-z Universe.
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All authors P. Bianchini, A. L. Varri, A. Askar, A. Marklund, A. Mastrobuono-Battisti
High Energy Astrophysical Phenomena
Single-Pulse Study of the Pseudo-nulling Pulsar PSR J1820-0509 Based on FAST Observations
Zefeng Tu, Rushuang Zhao, Hui Liu et al. (+14 more)
Using two observations obtained with the Five-hundred-meter Aperture Spherical
radio Telescope (FAST), we present a detailed single-pulse analysis of the high-nulling
pulsar PSR J1820-0509. We measure an exceptionally high nulling fraction of approximately 81.78%, significantly exceeding previous estimates from Parkes observations. The single-pulse energy distribution exhibits a clear bimodal structure, consistent with classical nulling behavior. However, stacking the identified null pulses reveals a statistically significant residual profile above the noise level, indicating that the nulls correspond to a very weak emission state rather than a complete cessation of
radio emission. The
pulsar shows clustered burst activities spanning several hundred rotation periods, with prominent quasi-periodicities at 1191 +/- 81 and 590 +/- 15 pulse periods in the two observations. Based on temporal clustering and integrated profile morphology, we identify three distinct emission modes (A, B, and C) and a pseudo-null state (D). These modes exhibit systematic differences in pulse morphology, polarization, and energy statistics. The pulse width-energy relations reveal clear transitions between low- and high-energy regimes. The energy distributions of Modes A and C are well described by lognormal functions, while Mode B follows a composite Gaussian-lognormal distribution. These results suggest that the
radio emission of PSR J1820-0509 is governed by multiple quasi-stable magnetospheric states. The presence of weak emission during pseudo-nulls, together with systematic mode-dependent variations, supports the interpretation that
pulsar nulling reflects transitions between different magnetospheric activity levels rather than a complete shutdown of emission.
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All authors Zefeng Tu, Rushuang Zhao, Hui Liu, Biping Gong, D.Li, P.Wang, Chenchen Miao, Q.J.Zhi, S.J.Dang, S.D. Wang, Q. Zhou, Z.J. Zhang, Xu Zhu, R.W. Tian, H.W.Xu, Yi Zhou, D.Y. Yan
High Energy Astrophysical Phenomena
Inherent self-consistency of the electron fraction between neutrino-dominated accretion flows and their progenitors
Rui-Qi Cui and Tong Liu
Stellar-mass black holes (BHs) surrounded by
neutrino-dominated
accretion flows (NDAFs) are a leading central engine of gamma-ray bursts (GRBs). In this work, we investigate the electron fraction distribution in NDAFs with or without disk
outflows for different
accretion rates, BH
spins, and
outflow rates. As the results, for the cases of the massive disks at relatively low
accretion rates, the outer boundary of the disks are predominantly advection-cooled, yielding electron fractions of \(Y_{\rm e} \sim 0.5\), as expected for massive collapsar progenitors. By contrast, in the cases of lower-mass disk at high
accretion rates,
neutrino cooling becomes highly efficient and mildly electron-degenerate disks emerge, characterized by \(Y_{\rm e} \lesssim 0.38\) at the outer boundary of the disk, even for the strong
outflows, which is consistent with materials from compact object merger scenarios. Moreover, we find that these trends remain robust across different BH
spins. Consequently, the self-consistent agreement between the electron fraction properties at the outer boundaries of NDAFs and those expected from GRB progenitors provides effectively support for NDAFs serving as the GRB central engines.
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Solar and Stellar Astrophysics
Direct evidence for magnetohydrodynamic disk winds driving rotating outflows in protostar HOPS 358
Chul-Hwan Kim, Jeong-Eun Lee, Doug Johnstone et al. (+4 more)
Angular momentum removal is a fundamental requirement for
star and
planet formation, yet the mechanisms driving this process remain debated. Magnetohydrodynamic disk winds, launched along
magnetic field lines from extended disk regions, offer a promising solution, particularly in regions where magnetorotational
turbulence is weak. Here we present high-resolution Atacama Large Millimeter/submillimeter Array observations of the Class 0 protostar HOPS 358, revealing a rotating, nested
outflow structure traced by H2CO, SO, and CH3OH emission. The
outflow preserves the disk's rotational sense and is aligned with the disk axis, providing direct observational evidence for a magnetically launched disk wind. From the measured kinematics, we derive a dimensionless
magnetic lever arm of approximately 2.3 and constrain the wind-launching region to radii of 10-18 astronomical units within the
planet-forming zone. These results demonstrate that magnetohydrodynamic disk winds operate during the deeply embedded phase, efficiently extracting angular momentum while shaping disk
evolution and establishing initial conditions for
planet formation.
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All authors Chul-Hwan Kim, Jeong-Eun Lee, Doug Johnstone, Gregory J. Herczeg, Chin-Fei Lee, Logan Francis, Patrick D. Sheehan
High Energy Astrophysical Phenomena
Exploring LSST's capabilities for early detection of outbursts in low-mass X-ray binaries
Susmita Sett, Arash Bahramian, Kristen Dage et al. (+2 more)
Following long periods of quiescence, low-mass X-ray binaries can exhibit intense X-ray outbursts triggered by instabilities within the
accretion disk. These outbursts can sometimes be detected in optical wavelengths before being detected in X-rays, acting as an early onset warning and enabling a deep study of
accretion disk properties informed by the lag between optical and X-ray rise. We explore the potential of Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) to detect these outbursts early through optical observations. We evaluate the capabilities of LSST based on currently planned survey cadence, filter-specific depth, and other observational factors that affect early detection. We develop and apply an extended metric to assess outburst detectability and recovery fraction. We find that despite inherent potential for early detection of XRB outbursts, the currently planned survey strategy makes it challenging to detect early onset of XRBs. Lastly, we demonstrate how this estimate can be used to infer the wider LMXB population in the
Galaxy as the LSST progresses.
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All authors Susmita Sett, Arash Bahramian, Kristen Dage, David Russell, William I.Clarkson
High Energy Astrophysical Phenomena
The muon charge asymmetry and the directional distribution of thunderstorm events observed by the GRAPES-3 muon telescope
B. Hariharan, S.K. Gupta, Y. Hayashi et al. (+12 more)
The electric fields inside thunderstorms can significantly modify the intensity of secondary
cosmic ray
muons at the ground level, producing measurable variations in their intensity ($\Delta$I$_{\mu}$). By utilizing the decade-long observations of thunderstorms (April 2011-December 2020) by the GRAPES-3
muon telescope (G3MT), a directional asymmetry in $\Delta$I$_{\mu}$ is observed, with nearly six times more events being detected from the east than the west directions. Using detailed CORSIKA Monte Carlo simulations, it is shown that this asymmetry is caused by the variations of the
muon charge ratio R$_\mu$ (N$_{\mu^+}$/N$_{\mu^-}$). The anisotropic R$_\mu$ in turn, is caused by the systematic changes in geomagnetic cutoff
rigidities, and subsequent selective filtering of predominantly positively charged primary
cosmic rays. As a consequence, the R$_\mu$ increases systematically from west to east across the G3MT field of view, enhancing the sensitivity of east directions to positively charged thunderstorm top. Monte Carlo simulations with constant R$_\mu$ show that the directional asymmetry disappears, demonstrating the
muon charge imbalance to be the dominant driver of the observed asymmetry. The dependence of R$_\mu$ on the hadronic interaction is also studied by comparing seven combinations high-, and low-energy hadronic interaction generators, which show a $\lesssim$7% spread in R$_\mu$, and $\lesssim$14% variation in the derived thunderstorm potentials. These results provide the first quantitative link between the
muon charge asymmetry caused by the geomagnetic field, and the directional distribution of thunderstorms, reinforcing the role of
muon observations as a probe of gigavolt potentials in atmospheric electrical structures.
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All authors B. Hariharan, S.K. Gupta, Y. Hayashi, P. Jagadeesan, A. Jain, S. Kawakami, H. Kojima, P.K. Mohanty, Y. Muraki, P.K. Nayak, A. Oshima, M. Rameez, K. Ramesh, L.V. Reddy, S. Shibata
Solar and Stellar Astrophysics
Toward a Comprehensive Grid of Cepheid Models with MESA. III. Evolutionary and Pulsation Relations for Models with Core and Envelope Overshooting
R. Smolec, O. Ziółkowska, R. Singh Rathour et al. (+2 more)
Evolutionary tracks for 2-8M$_\odot$ models, covering a [Fe/H]=$-$1.0 ($Z=0.0014$) to [Fe/H]=+0.2 ($Z=0.02$)
metallicity range are computed with Modules for Experiments in
Stellar Astrophysics, MESA, to investigate evolutionary and pulsation properties of classical, fundamental mode Cepheids. We examine in detail the effects of convective overshooting from the Main Sequence core, as well as from the convective envelope on the Red
Giant Branch. Mass loss is also included in a few model sets. Linear pulsation properties are derived consistently with a module of MESA, Radial
Stellar Pulsation, RSP. We provide edges of the classical Instability Strip, as well as ages, crossing times through the Instability Strip and period change rates. Period-Luminosity, Mass-Luminosity, Period-Radius and Period-Age relations are provided, both in analytical and tabular form. Their dependence on
metallicity, crossing number and overshooting parameters are investigated. Qualitative comparisons with classical Cepheids in the Milky Way and Magellanic Clouds as well as other theoretical relations are presented. We find satisfactory agreement for most of the observables and good match with other theoretical work, however reproducing short-period Cepheids in the Small Magellanic Cloud as well as Cepheid mass discrepancy pose a challenge for the presented models. Considering
metallicity effect of the Period-Luminosity relation, we find $\gamma\approx -0.20$ mag dex$^{-1}$, nearly independent on photometric pass band and in good agreement with recent observational studies. The magnitude of this effect depends on the underlying mass-luminosity relation, being stronger for relations that predict higher luminosities at a given mass.
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All authors R. Smolec, O. Ziółkowska, R. Singh Rathour, V. Hocdé, P. Wielgórski