Astrophysics of Galaxies
The quest for high-redshift radio galaxies II. Discovery of the most powerful known radio galaxy at z=4.946
B.Balmaverde, A.Capetti, M.Chiaberge et al. (+3 more)
As part of our quest for high-
redshift radio galaxies (HzRGs), we present the results obtained from optical spectroscopy leading to the confirmation of one HzRG candidate selected using the Lyman break technique. The optical emission, associated with the
radio source TXS 2354+015, exhibits a prominent drop in the r band, which is characteristic of sources at z~5. The optical spectrum shows a bright asymmetric emission line, with a large equivalent width of ~900 Angstrom. Its identification with the Ly$\alpha$ line is confirmed by the detection of the NV$\lambda$1640, leading to a
redshift estimate of z=4.946. Its broadband
radio spectrum is well reproduced using a power law with a slope of 0.94. The
radio luminosity at the rest frame frequency of 500 MHz is 6.2e29 W/Hz. This result makes this source the most powerful
radio galaxy currently known.
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All authors B.Balmaverde, A.Capetti, M.Chiaberge, F.Massaro, M. Coloma Puga, A. Jimenez-Gallardo
High Energy Astrophysical Phenomena
Probing the Metallicity Dependence of Fast Radio Burst Progenitors with CHIME/FRB Outrigger Dwarf Host Galaxies
Y. Dong, W. Fong, K. Nimmo et al. (+24 more)
Using the fast
radio bursts (FRBs) localized with the CHIME/FRB Outriggers between February and October 2025, we conduct a systematic search for dwarf host
galaxies. We identify and characterize eight host
galaxies for one repeating and seven apparently non-repeating FRBs, newly classifying five hosts as dwarfs with stellar masses of $\log(M_\ast/M_\odot) \approx 8.1-9.1$. We measure their gas-phase
metallicities and, when combined with hosts from the literature, finding that repeating and non-repeating FRBs have statistically distinct
metallicity distributions. Non-repeating FRBs inhabit relatively metal-rich environments ($12 + \rm log( O/H) \gtrsim 8.35$) across the full observed mass range, while repeating FRBs have significant preference for dwarf
galaxies with $12 + \rm log( O/H) \lesssim 8.35$. Almost all repeaters associated with persistent
radio sources (PRSs) are in dwarfs with $12 + \rm log( O/H) \lesssim 8.15$, suggesting a connection between repeaters in metal-poor dwarf environments and PRS formation. We also calculate the host dispersion measure ($\mathrm{DM}_{\rm host}$), Faraday rotation measure ($\mathrm{RM}_{\rm host}$), and scattering timescale ($\tau_{\rm host,1~GHz}$) for 54, 37, and 24 FRBs, respectively, including both our sample and FRBs in the literature. We find no significant ($>3\sigma$) correlation between host
metallicity and $\mathrm{DM}_{\rm host}$, $\mathrm{RM}_{\rm host}$, or $\tau_{\rm host,1~GHz}$. The distinct host
metallicities of apparently non-repeating and repeating FRBs may reflect
metallicity-dependent massive-
star evolution, with repeating FRBs and PRSs requiring more extreme magnetar birth
spins than the predominantly non-repeating FRB population.
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All authors Y. Dong, W. Fong, K. Nimmo, N. Loudas, B.C. Andersen, S. Andrew, A. Cai, S. Chatterjee, A.M. Cook, A.P. Curtin, T. Eftekhari, B.M. Gaensler, J. Hessels, V.M. Kaspi, A. Khan, C. Leung, L. Mas-Ribas, K. Masui, A. Moroianu, A.B. Pearlman, J.X. Prochaska, M.W. Sammons, P. Scholz, K. Shin, S. Simha, M. Woodland, Z. Zhuang
Cosmology and Nongalactic Astrophysics
Wave-Optics Imprints of Warm Dark Matter Subhalos with Prompt Cusps on Strongly Lensed Gravitational Waves
Bhashin A. Thakore and Shin'ichiro Ando
Dark matter
halos are expected to form with a
prompt $\rho \propto r^{-3/2}$ density cusp at their centres, and in warm dark matter (WDM) cosmologies these cusps can dominate the inner structure of the low-mass subhalos that survive free-streaming suppression. We investigate whether that inner structure is visible to gravitational waves lensed in the wave-optics (WO) regime. Extending the strong
lensing WO diffraction-integral framework to WDM, we generate subhalo populations with the sashimi-w semi-analytic model, assign each subhalo a
prompt cusp through a cusp-
halo relation, and compute the frequency-dependent amplification factor $F(f)$ across the LISA band over 500 independent realisations for $m_\chi \in \{6, 10, 20, 40, 80, 100\}$~keV. The signal is governed by the overlap between the WDM-suppressed subhalo mass function and the $m_{\rm sub} \sim 10^{4}$ to $10^{7}\,M_\odot$ range to which the LISA band is sensitive. Modulations are negligible for $m_\chi \lesssim 10$~keV, reach the percent level by 40~keV, and then saturate to a CDM-like plateau, so the observable reliably probes $m_\chi$ only over the intermediate range $\sim 20$ to 40~keV. Repeating the 40~keV ensemble on identical subhalo catalogs with the cusp amplitude set to zero, we find that
prompt cusps enhance the amplitude modulation only mildly. Where cusps make up a large fraction of the subhalo mass, free-streaming has already depleted the signal-carrying mass range, and where that range is populated, the cusp lies well inside the Fresnel radius, to which the diffraction integral responds through projected enclosed mass rather than central density. A percent-level detection in a strongly lensed massive black-hole binary would therefore establish the presence of substructure on Fresnel scales without diagnosing its inner profile.
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Instrumentation and Methods for Astrophysics
A Practical Primer on Software Citation in Research
Floor S. Broekgaarden, Phil R. Van-Lane, Sasha Levina et al. (+9 more)
Software underlies virtually all modern research, yet citation practices for software remain inconsistent and often inadequate. This short primer offers practical guidance in two directions: how to properly cite the software you use in your research, and how to make your own software easy for others to cite. We describe a seven-step workflow for citing software and a five-step workflow for making your software citeable, along with the community tools and resources that support each step. We also address common questions about what software, and how much, to cite. The guidance is field-independent; we use astronomy as a running example throughout, and readers in other disciplines can substitute the equivalent tools and conventions of their own community. Our goal is to lower the practical barrier to good software citation practice and to support a research culture in which software receives the scholarly credit it deserves.
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All authors Floor S. Broekgaarden, Phil R. Van-Lane, Sasha Levina, Ahmed Bello, Sandra Gesing, Daniel S. Katz, Bhavesh Patel, Pengyin Shan, Samantha Teplitzky, Simon Thill, Peter K. G. Williams, Andrea Zonca
Earth and Planetary Astrophysics
Just a Phase? Weakening Vertical Shear Instability Explains Class II Disk Morphologies: Simulations with dust coagulation, sedimentation, thermal relaxation, and backreaction
Thomas Pfeil, Alexandros Ziampras, Shangjia Zhang et al. (+2 more)
The Vertical Shear Instability (VSI) is known to create
turbulence and strong vertical mixing in protoplanetary disks if thermal relaxation is sufficiently fast. In simulations where this condition is met, VSI can loft dust particles to large altitudes, creating a vertically extended appearance in mock millimeter-wavelength observations, which is inconsistent with the morphology of the majority of observed class II disks. We present simulations of protoplanetary disks with VSI that are consistent with the observed thin-disk geometries, while maintaining the commonly observed bowl-shaped morphology in scattered light images at micrometer wavelength. We show that this outcome arises naturally when the effects of dust coagulation, sedimentation, and dust-gas thermal accommodation are taken into account. Sedimentation-driven coagulation removes large amounts of dust from the disk atmosphere, in the process slowing down the dust-driven cooling of the gas. At the same time, a dense midplane layer of millimeter-sized grains forms, which exerts aerodynamic drag on the gas. This results in the termination of the VSI's corrugation mode. Only weak VSI activity remains in the upper and lower hemispheres. These processes occur on the typical dust growth timescale and suppress strong VSI-induced
turbulence within a few hundred thousand years. VSI could thus generally be restricted to the class I evolutionary stages of protoplanetary disks.
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All authors Thomas Pfeil, Alexandros Ziampras, Shangjia Zhang, Philip J. Armitage, Yan-Fei Jiang
Instrumentation and Methods for Astrophysics
The shell around VY Canis Majoris in SPHEREx is likely an artifact
Viraj Karambelkar, Yashvi Sharma and Kishalay De
Recently, the presence of a large shell around the bright hypergiant
star VY Canis Majoris was reported in images from the SPHEREx mission. We report similar shells around other bright
stars at similar locations in SPHEREx Band 1 images, suggesting that this shell is not astrophysical but instead a detector artifact.
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Instrumentation and Methods for Astrophysics
AstroGenesis: A Domain-Specific Multi-Agent AI for Astrophysical Research
N. Sahakyan, M. Khachatryan, A. Mahabal et al. (+13 more)
Modern astrophysical research requires the integration of rapidly expanding scientific literature, heterogeneous observational data, and increasingly complex physical models. We introduce AstroGenesis (https://astrogenai.com), a domain-specific multi-
agent AI framework that integrates literature
retrieval, multiwavelength data access and analysis, theoretical modeling, and research ideation within a unified research environment.The current implementation focuses on blazar research, with specialized
agents coordinated by a Supervisor
Agent and Planner/Replanner architecture. These
agents provide capabilities for retrieving and synthesizing literature, accessing and analyzing multiwavelength observations, performing physical modeling, and identifying research directions. A central component is the Theoretical Modeling
Agent, which uses pretrained neural-network surrogate models to enable efficient broadband and multimessenger modeling through natural-
language interaction. The framework provides natural-
language access to science-ready multiwavelength observational data and
retrieval-grounded literature through a multi-stage
retrieval and ranking pipeline. The literature-
retrieval system was evaluated using two
benchmarks: a single-paper
benchmark, in which each question targets one publication, and a multi-paper
benchmark, in which questions may require evidence from several publications. At least one relevant publication was retrieved among the top five results for 76.6% of the single-paper questions and 79.2% of the multi-paper questions. Representative workflows demonstrate how literature, observational data, physical modeling, and hypothesis generation can be combined within traceable analyses. The framework is extensible to additional astrophysical domains, with the goal of streamlining research workflows and enabling efficient, connected, and reproducible scientific investigations.
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All authors N. Sahakyan, M. Khachatryan, A. Mahabal, D. Pasham, A. Khachatryan, V. Markosyan, N. Unkovskii, V. Vardanyan, D. Bégué, P. Giommi, G. Harutyunyan, D. Israyelyan, A. Tramacere, A. Casotto, Y. Wang, D. Li
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Finite-Temperature Axion-Admixed Neutron Stars in a Quarkyonic Crossover Framework
S. K. Patra, D. Dey, Jeet Amrit Pattnaik et al. (+1 more)
We analyze the effect of
axion contribution on the mass, radius and dimensionless deformability of a
neutron star (NS) at finite temperature. Although the cooling of an NS is mainly due to the emission of
neutrinos, additional cooling cannot be ruled out due to the emission of
axions. The existence of an
axion is needed for addressing the strong CP problem within the standard model. The Peccei-Quinn (PQ)
symmetry breaking mechanism generates
axions. They are pseudo-Nambu-Goldstone
bosons. Their mass is extremely small but non-zero. This naturally resolves the fine-tuning problem of the strong CP-violating parameter ${\theta} \lesssim 10^{-10}$. We propose that a finite temperature NS feature a
quark core surrounded by a baryonic medium admixed with the
axions, which are pseudo scalar Goldstone
bosons and are considered as strong candidates for the dark matter (DM). Unlike the original quarkyonic model, we formulate a quarkyonic-inspired smooth crossover equation of state (EoS) at finite temperatures. This smooth crossover avoids thermodynamic instabilities found in sharp first-order constructions. We add the axionic EoS to the finite temperature quarkyonic one and solve the Tolman-Oppenheimer-Volkoff equations to estimate the properties of the NS both with and without taking the
axion into account at different temperatures. We find that the production of
axions is maximum within a radius of $5-11$ km in the
star's interior; however, the impact on the mass is significant, i.e., $\sim 60\%$ of
axion mass concentrated in the central region of the
star. We also find that the effect of temperature on the mass of NS is marginal unlike the radius. In general, the influence of
axions is significant for the observational properties of NS. These results highlight the pivotal role of
axion physics in
neutron star phenomenology.
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All authors S. K. Patra, D. Dey, Jeet Amrit Pattnaik, R. N. Panda
Astrophysics of Galaxies
A sub-100 pc view at z~5 of a Multiply-Imaged Massive Quiescent Galaxy
Richard Pan, Danilo Marchesini, Joseph F. V. Allingham et al. (+34 more)
Recent James Webb Space
Telescope spectroscopic surveys reveal an abundance of rapidly assembled early
galaxies in the first billion years. Cosmological simulations struggle to reproduce this population because models require a rapid, highly efficient conversion of baryons into
stars followed by an abrupt cessation of
star-formation, known as quenching, in the early Universe. Testing these theoretical models remains difficult because high-
redshift field
galaxies appear compact and unresolved. This lack of resolution makes it impossible to distinguish compaction-driven quenching from secular
evolution. Here we present VENUS-CLJ0152-QG1, a massive post-starburst
galaxy at $z=5.18\pm0.15$, with inferred low-levels of
star-formation in the last 30 Myr. The foreground cluster CL J0152.7-1357 gravitationally lenses the system into three images with median magnifications of $\mu \sim$ 7, 11, and 0.6. This geometry yields a physical resolution of $\sim 70$ pc, a factor of $\sim 7$ better than the JWST/NIRCam fundamental blurring limit (full-width half-maximum of $\sim$0.48 kpc at $z\sim5$). Our two-dimensional mapping reveals a half-light radius twice as large as expected, a central stellar mass surface density half a dex lower than field analogs, and off-center ionized gas emission. Together, these features show that VENUS-CLJ0152-QG1 abruptly ceased
star formation in the absence of a compaction event or an obvious active galactic
nucleus. Consequently, this
galaxy shows that unresolved observations likely overestimate the global densities of early
galaxies, and that theoretical models require alternative pathways to quench massive sources without relying on compaction or unobscured AGN.
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All authors Richard Pan, Danilo Marchesini, Joseph F. V. Allingham, Seiji Fujimoto, Adi Zitrin, Dan Coe, Vasily Kokorev, Lukas J. Furtak, Jacqueline Antwi-Danso, Yoshihisa Asada, Franz E. Bauer, Maruša Bradač, Larry D. Bradley, Chloe M. Cheng, Pratika Dayal, Andreas L. Faisst, Brenda L. Frye, Norman A. Grogin, Tiger Yu-Yang Hsiao, Gourav Khullar, Anton M. Koekemoer, Conor Larison, Ray A. Lucas, Vladan Markov, Nicholas S. Martis, Minami Nakane, Gaël Noirot, Johan Richard, Massimo Ricotti, Luke Robbins, Fengwu Sun, Francesco Valentino, Eros Vanzella, Chris Willott, Rogier A. Windhorst, Hiroto Yanagisawa, Anita Zanella
High Energy Astrophysical Phenomena
First Pre-peak Ultraviolet Spectrum of a Tidal Disruption Event: A Fast Outflow Revealed Prior to Maximum Light in TDE2025aarm
Erica Hammerstein, Ryan Chornock, Jean Somalwar et al. (+32 more)
The tidal disruption and eventual
accretion of a
star by a massive black hole can lead to the launching of outflows and winds that encode important information about the tidal disruption and
accretion processes. However, little is known about the existence and behavior of these outflows before optical light-curve peak, when processes such as stream-stream collisions and disk formation may be important. Here, we present the first pre-peak ultraviolet (UV) spectrum of a tidal disruption event (TDE), obtained $\sim 20$ days before optical maximum light of the nearby (
redshift $z=0.0137$) TDE2025aarm, along with quasi-simultaneous infrared (IR) through X-ray observations. Our HST/STIS spectrum shows strong evidence for an early-time outflow through broad near-UV (NUV) and far-UV (FUV) absorption lines blueshifted by $\sim$10,000 km s$^{-1}$, including two new UV broad absorption features not yet identified in a TDE. We find that the FUV–IR continuum deviates significantly from a blackbody ($f_\lambda \propto \lambda^{-3.08}$), which we interpret as a signature of reprocessing through the outflow. This deviation implies that the bolometric luminosity in optical TDEs may be underestimated by a significant factor ($\sim$9 in this case) when inferred from single-temperature blackbody fits to NUV–optical photometry alone. This work further confirms that TDEs are capable of launching fast outflows at very early times and emphasizes the importance of
prompt FUV spectroscopic observations of TDEs that can capture the full continuum emission and energetics.
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All authors Erica Hammerstein, Ryan Chornock, Jean Somalwar, Raffaella Margutti, Brenna Mockler, Olivia Aspegren, Itai Sfaradi, Natalie LeBaron, Jonathan Carney, Alexei V. Filippenko, A.J. Nayana, Igor Andreoni, Thomas Brink, Peter J. Brown, Adam J. Burgasser, S. Bradley Cenko, Suvi Gezari, Xiaoshan Huang, Mansi M. Kasliwal, Jon M. Miller, Sasha Mintz, Sam Rose, Peter Senchyna, Joshua D. Simon, Emma Softich, Robert Stein, Yuhan Yao, WeiKang Zheng, Richard Dekany, Matthew J. Graham, Russ R. Laher, Josiah Purdum, Ben Rusholme, Jesper Sollerman, Stefan van der Walt
Instrumentation and Methods for Astrophysics
Differentiable astrophysics at scale: solving and differentiating ODE ensembles on the GPU
A. Spurio Mancini
Astronomers increasingly fit their models with gradient-based methods, such as
Hamiltonian Monte Carlo, which need the derivatives of the model with respect to its parameters. In many analyses a prediction requires solving a small system of ordinary differential equations (ODEs) for thousands to millions of parameter sets, and this ensemble of integrations often sets the cost of the analysis. We introduce to the astronomical community GRADSOLVE, a JAX library that moves this computation to graphics processing units (GPUs): it integrates each member of the ensemble in its own GPU thread with its own step size and returns the derivatives with respect to the parameters in the same pass. We measure the speed-up it provides in three examples from different fields of astronomy, stellar orbits in the Galactic potential, the expansion history of a dark-energy cosmology and the
spin precession of binary black holes, with every code held to the same accuracy requirement. For a million trajectories GRADSOLVE runs 8.5 to 1500 times faster than the serial CPU code of each example running on all 128 cores of a CPU, and several orders of magnitude faster than on one core. On the same GPU it is also 11 to 15 times faster than DIFFRAX, the state-of-the-art ODE library in JAX, in all three examples. With GRADSOLVE a million such integrations take seconds or less on one GPU, so gradient-based analyses that need ensembles of this size become routine. The code is publicly available at https://github.com/ECLIPSE-AI4Science/gradsolve.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Sterile Neutrino Dark Matter Cries for GeV Heavy Neutral Leptons
Marco Drewes, Yannis Georis, Juraj Klarić et al. (+2 more)
The ordinary and dark matter in the Universe may share a common origin in the framework of a minimal extension of the Standard Model by three right-handed
neutrinos. A pair of such heavy neutral leptons (HNLs) can give masses to
neutrinos, generate the baryon asymmetry at the electroweak scale and produce a large lepton asymmetry at the QCD scale, which is then resonantly transformed into an abundance of the third state that acts as sterile
neutrino dark matter. The minimality of this setup, known as
Neutrino Minimal Standard Model ($\nu$MSM), makes it highly predictive. Earlier attempts to pin down the properties of the HNLs based on the requirement to simultaneously explain the
neutrino masses as well as the baryonic and dark matter abundances were hampered by an incomplete understanding of the
quantum kinetic equations describing the HNLs throughout
cosmic history. We perform the first parameter scan of the $\nu$MSM in which this shortcoming has been overcome. We find that the $\nu$MSM provides a common explanation for all aforementioned phenomena only within a well-defined parameter space that is limited in all directions, with HNL masses kinematically accessible by the SHiP experiment as well as searches at the LHC and future lepton
colliders. Further predictions for the HNL decay branching ratios, CP-violation, and lepton number violation (LNV) make the model highly testable, bringing a discovery of the common origin of
neutrino masses and all matter in the Universe within reach of existing and planned experiments.
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All authors Marco Drewes, Yannis Georis, Juraj Klarić, Mikhail Shaposhnikov, Inar Timiryasov
High Energy Astrophysical Phenomena
Performance-portable GPU acceleration of the hybrid particle-in-cell code dHybridR
Bricker Ostler, Miha Cernetic and Damiano Caprioli
Hybrid particle-in-
cell simulations are widely used to study kinetic processes in collisionless astrophysical and space
plasmas, yet the high computational cost of large-scale three-dimensional runs has largely confined production studies to two dimensions or restricted domains. To address this challenge, we present a performance-portable GPU implementation of the hybrid particle-in-
cell code dHybridR. The implementation combines OpenMP target offloading with specialized SYCL kernels for the most computationally expensive operations, while preserving a unified CPU-GPU codebase that supports Intel, AMD, and NVIDIA GPUs. On the exascale supercomputers Aurora and Frontier, dHybridR achieves weak scaling efficiencies of $86\%$ to $97\%$ across 49,152 accelerators, and at 256 particles per
cell, its full-node GPU throughput is up to $32\times$ that of the vectorized CPU implementation at approximately $90\%$ less energy per particle-update. To our knowledge, no other hybrid particle-in-
cell code has reported GPU performance at this scale, leaving dHybridR uniquely positioned to exploit exascale systems. These advances substantially lower the computational barrier to large-scale three-dimensional hybrid-kinetic simulations of collisionless
plasmas.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Fermionic cosmic strings in dynamical Chern-Simons gravity
Stephon Alexander, Heliudson Bernardo and Shengyuan Zhang
We investigate topological defects produced by a chiral phase transition in a fermionic ultraviolet completion of dynamical Chern-Simons (dCS)
gravity. The model contains a complex scalar field with a chiral Yukawa coupling to
fermions. Below the chiral
symmetry breaking scale, integrating out the gapped bulk modes produces a gravitational Chern-Simons coupling which, we argue, modifies
cosmic string solutions from the phase transition. The resulting corrected string metric is supported by a generalization of the Callan-Harvey fermionic zero mode solution, in which the null current generated by these zero modes provides a mechanism for parity violation. In the weak-coupling and weak-
gravity regime, we derive the leading order-reduced dCS correction to this exterior metric. We also discuss the effective action description for generic string configurations in dCS
gravity. The gravitational Pontryagin term provides the anomaly inflow required to cancel the gravitational anomaly of the chiral worldsheet theory.
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Solar and Stellar Astrophysics
A Search For Stellar-mass Black Holes Via Astrometric Microlensing II: 2012-2015 Keck Candidates
Mace J. Huston, Jessica R. Lu, Casey Y. Lam et al. (+55 more)
The Milky Way is expected to host $\sim$10$^8$ stellar-mass black holes with an uncertain binary fraction. The only proven method to detect isolated stellar mass black holes is gravitational microlensing. Here we report the results of a microlensing search for black holes with photometry and astrometry. By combining 10 years of seeing-limited photometry from OGLE and MOA with diffraction-limited photometry and astrometry from adaptive optics imagers at the W.~M.~Keck Observatory, we constrain lens masses for OGLE-2012-BLG-0169, OGLE-2014-BLG-0613/MOA-2015-BLG-041, OGLE-2015-BLG-0029/MOA-2015-BLG-170, and OGLE-2015-BLG-0211. Of the four long-duration microlensing events monitored, we ruled out black hole lenses in 3 events, which likely have stellar or white dwarf lenses. OGLE-2015-BLG-0211 remains a black hole candidate with a poorly constrained lens mass with a 1$\sigma$ upper mass limit of 3.2$M_\odot$ and a 3$\sigma$ upper mass limit of 21.6$M_\odot$. This event suffered from poor observing conditions and significant astrometric reference frame uncertainties, but its analysis may benefit from additional astrometric data in the upcoming Gaia Data Release 4. Of the six long-timescale ($t_E>100$ days) microlensing events from this work and previous studies, one black hole has been confirmed with a second not ruled out. We briefly examine Galactic model simulations and find that our result agrees with current expectations. Ultimately, we need a larger sample of isolated black holes to constrain their formation processes. This will be possible in the coming years with Rubin and Roman, as well as improved astrometry from JWST and large, ground-based
telescopes equipped with adaptive optics.
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All authors Mace J. Huston, Jessica R. Lu, Casey Y. Lam, J. Nijaid Arredondo, Natasha S. Abrams, Shep Brooke, Sage H. Remulla, Eran Ofek, Michael S. Medford, Fatima Abdurrahman, Shrihan Agarwal, Edward Broadberry, Matthew Freeman, Matthew W. Hosek Jr., Siyao Jia, Sean K. Terry, The OGLE Collaboration: Andrzej Udalski, Przemek Mroz, Radoslaw Poleski, Jan Skowron, Michal K. Szymanski, Igor Soszynski, Pawel Pietrukowicz, Szymon Kozlowski, Krzysztof Ulaczyk, Krzysztof A. Rybicki, Patryk Iwanek, Marcin Wrona, Mariusz Gromadzki, Mateusz J. Mroz, Michal Malkowski, The MOA Collaboration: Fumio Abe, David P. Bennett, Aparna Bhattacharya, Ian A. Bond, Kotaro Daimon, Ryusei Hamada, Yuki Hirao, Shuma Makida, Stela Ishitani Silva, Shota Miyazaki, Yasushi Muraki, Tutumi Nagai, Kansuke Nunota, Ryo Ogawa, Ryunosuke Oishi, Hideaki Ose, Greg Olmschenk, Clement Ranc, Nicholas J. Rattenbury, Yuki K. Satoh, Takahiro Sumi, Daisuke Suzuki, Takuto Tamaoki, Chihiro Ueda, Paul J. Tristram, Aikaterini Vandorou, Hibiki Yama
Instrumentation and Methods for Astrophysics · Cross-listed from stat.AP
Multivariate Continuous-Time Autoregressive Moving Average Processes for Astronomical Multiband Time Series
Izak Schmidlkofer, Zhirui Hu, Lishan Shi et al. (+2 more)
Large-scale astronomical surveys provide unprecedented volumes of multivariate time-series observations obtained through multiple optical filters. We develop a structured multivariate continuous-time autoregressive moving average (MCARMA) framework for multi-band time series with irregular sampling, heteroscedastic measurement errors, and partially observed bands. The framework allows band-specific
stochastic dynamics while modeling cross-band dependence through correlated Brownian driving processes, with state-space and spectral representations enabling likelihood-based inference and interpretation of the fitted
stochastic dynamics. We develop a two-stage estimation procedure in which a numerically stabilized preliminary fit initializes subsequent maximum likelihood estimation. Simulations show that higher-order
stochastic structure can be recovered when its characteristic features are adequately resolved, but can become weakly identifiable because of limited temporal resolution or near pole–zero cancellation. Joint multivariate estimation improves parameter recovery in 23 of 27 settings and spectral recovery in 26 of 27 settings relative to separate single-band fits. Three Sloan Digital Sky Survey Stripe 82
quasars, respectively favoring MCARMA(1,0), MCARMA(2,0), and MCARMA(2,1), illustrate how joint multiband modeling uses cross-band dependence to inform marginal dynamics and can yield different model-order and spectral inference. The methodology is implemented in the Python package mcarma.
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All authors Izak Schmidlkofer, Zhirui Hu, Lishan Shi, Weixiang Yu, Hyungsuk Tak
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Strange Quark Stars and Spontaneous Scalarization
Mina Mehraeen Nazdik and Zeinab Rezaei
Strange
quark matter, as one of the most extreme dense states in astrophysics, can be explored through relativistic compact objects. Hypothetical relativistic
stars composed of dense strange
quark matter are characterized by the equation of state of that matter. The spontaneous scalarization of strange
quark stars is influenced by the equation of state of strange
quark matter. Here, we investigate how the equation of state of strange
quark matter influences the spontaneous scalarization of these
stars. Considering Normal, color-flavor-locked (CFL), and CFLm
quark matter in the bag models and applying the scalar-tensor
gravity, we calculate the structure of scalarized strange
quark stars. We investigate how the effective bag constant, perturbative QCD parameter, CFL pairing gap, and strange
quark mass control the mass-radius relation, the central scalar field, the scalarization thresholds, and the scalar charge. Our results demonstrate that strange
quark stars in scalar-tensor
gravity are viable, testable objects, and they establish a complete framework for constraining both the gravitational theory and the properties of cold
quark matter with current and future multimessenger observations.
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Astrophysics of Galaxies
Interstellar extinction of classical Cepheids from neighboring stars I. Methodology and application to 16 Galactic Cepheids
Wilma Kiviaho, Pierre Kervella, Mika Juvela et al. (+21 more)
Galactic Cepheid variable
stars are fundamental calibrators of the
cosmic distance scale through their Period-Luminosity (PL) relation. The high-precision parallaxes expected from Gaia Data Release 4 (DR4) will enable a calibration of the Milky Way PL relation with unprecedented precision. This will place stringent requirements on interstellar extinction corrections, which remain a dominant source of uncertainty. We strive to derive highly accurate extinction values for Galactic Cepheids. We present an innovative methodology relying on the analysis of neighboring field
stars and apply it to a pilot sample of 16 Cepheids. We identify physically near field
stars using Gaia DR3 astrometry. For these
stars, we determine atmospheric parameters from medium- to high-resolution VLT/FLAMES spectroscopy. Fixing these parameters, we derive individual extinctions by fitting spectral energy distributions constructed from Gaia XP spectra and infrared photometry. We then reconstruct the three-dimensional distribution of extinction and interpolate extinction to the Cepheid position. We report extinction Av, total-to-selective extinction ratio Rv, and color excess E(B-V) for all 16 Cepheids. Our method achieves a mean precision of approximately 5%, improving upon typical literature values, with no significant systematic offset detected. We demonstrate that using field
stars bypasses uncertainties associated with Cepheid variability and can provide robust extinction estimates for Galactic Cepheids.
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All authors Wilma Kiviaho, Pierre Kervella, Mika Juvela, Alexandre Gallenne, Nicolas Nardetto, Carine Babusiaux, Rosine Lallement, Vincent Hocdé, Garance Bras, Nancy Remage Evans, Antoine Mérand, Grzegorz Pietrzyński, Gergely Hajdu, Henryka Netzel, Ricardo Salinas, Bogumił Pilecki, Cezary Gałan, Frédéric Arenou, Manon Bailleul, Katia Sivkova, Daniela González, Louise Breuval, Rajeev Singh Rathour, Brankica Apostolova
Cosmology and Nongalactic Astrophysics
The Lumina Project: Morphology of Ionized Bubbles and Neutral Islands
Meredith Neyer, Aaron Smith, Ali Sadain et al. (+10 more)
The Epoch of Reionization is characterized by the nucleation, expansion, and percolation of ionized bubbles in the intergalactic medium. Interpreting emerging multi-wavelength observations from facilities such as JWST and next-generation 21 cm interferometers requires a detailed theoretical understanding of the 3D morphology of these HII regions and of the residual neutral structures that survive near the end of reionization. We analyze the geometry and physical properties of ionized bubbles and late-time neutral islands in the large-volume 500 Mpc$^3$ radiation-hydrodynamics simulation Lumina. We identify discrete structures with a 3D watershed method and measure their volumes, shape tensors, and internal gas properties. The volume-weighted bubble size distributions evolve substantially across the EoR: characteristic radii shift from Reff~1 cMpc at z>10 to Reff>100 cMpc by z< 6, while watershed-derived sizes exceed line-of-sight mean-free-path measurements by roughly a factor of 3 at intermediate
redshifts. The bulk bubble population is predominantly prolate through most of the EoR. By z~6, however, the volume-weighted distribution of the triaxiality parameter T, which distinguishes flattened from elongated structures, becomes bimodal in the fiducial segmentation, with a sharp oblate peak near T~0.25 associated with a small number of very large bubbles during late percolation. The properties of bubble interiors are consistent with inside-out reionization, with median gas overdensities within bubbles decreasing from $\delta$~1 at z=15 toward the
cosmic mean by z=6. Beyond a minimum near the resolution scale, the median internal UV radiation energy density increases with bubble size. The residual neutral islands at z< 6 peak in volume-weighted size near Reff~10 cMpc and remain predominantly prolate, consistent with anisotropic residual neutral structure near the end of reionization.
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All authors Meredith Neyer, Aaron Smith, Ali Sadain, Oliver Zier, Mark Vogelsberger, Teodora-Elena Bulichi, Xuejian Shen, Sonja M. Koehler, Volker Springel, Rahul Kannan, Rongrong Liu, Lars Hernquist, Changhyun Cho
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Big Bang Nucleosynthesis as a Probe of First-Order Phase Transitions
Masanori Tanaka
Supercooled cosmological first-order phase transitions (FOPTs) generate a large temperature inhomogeneity due to their
stochastic reheating process. If a baryon asymmetry production predates the FOPT and is conserved during it, the temperature contrast is transferred onto the baryon-to-
photon ratio $\eta$ or the baryon-to-
entropy ratio $Y_{B}$, producing an inhomogeneity probed by big bang nucleosynthesis (BBN). We extend a recent formalism for this effect by including the reheating dependence of the induced $Y_{B}$ fluctuations, combining the transition-time power spectrum from finite-bubble statistics with
proton and
neutron diffusion at the BBN epoch. When the nucleation temperature is in the range $10^{-2}\,{\rm GeV} \lesssim T_{n} \lesssim 10^{2}\,{\rm GeV}$, the precise measurement of deuterium abundances disfavors parameter regions with a sizable latent heat and a long transition duration at the $1 \sigma$ level. The bound weakens towards higher $T_{n}$ as
diffusion becomes more efficient. We further show that this bound disfavors FOPT parameter regions compatible with the NANOGrav gravitational wave signal. This conclusion assumes that the baryon asymmetry predates the transition and that the fluctuation spectrum remains valid down to sub-bubble scales. Therefore, in such FOPT explanations of the NANOGrav signal, the baryon asymmetry cannot simply predate the transition. It can instead be generated after reheating or during the transition if the local baryon production tracks the local
entropy injection. As a result, the timing of baryogenesis may be constrained by combining gravitational wave observations with light element abundance measurements.
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Cosmology and Nongalactic Astrophysics
Entropy applications in cosmology: spacetime thermodynamics, holographic dark energy, entropic gravity and beyond - a review
Emmanuel N. Saridakis, Giuseppe Gaetano Luciano, Andreas Lymperis et al. (+1 more)
Entropy has emerged as a key concept at the intersection of
gravity,
quantum theory, and cosmology, revealing deep connections between geometry, information, and thermodynamics. The realization that black holes are thermodynamic systems, characterized by an
entropy proportional to their horizon area, has provided evidence that spacetime itself may possess a microscopic structure. Since then,
entropy has acquired a central role across
quantum field theory, holography,
quantum gravity, and cosmology. In this review, we present a unified account of
entropy in gravitational and cosmological contexts. We first survey
entropy in gravitational systems, focusing on black-hole thermodynamics,
entropy bounds, the holographic principle,
entanglement entropy, and the area law, together with the main corrections and generalizations arising from
quantum field theory, generalized uncertainty principles, modified statistics, and extended theories of
gravity. We then discuss three conceptually distinct ways in which
entropy is employed in cosmology. The first is through the spacetime-thermodynamics
conjecture, in which gravitational dynamics emerge from thermodynamic relations applied to cosmological horizons, and generalized
entropy forms consequently lead to modified cosmological
evolution. The second is the holographic approach, in which
entropy bounds constrain the
vacuum energy of the Universe, giving rise to the holographic dark energy scenario and its various extensions. The third is entropic
gravity, where
gravity is interpreted as an emergent phenomenon of entropic origin, leading to interesting cosmological phenomenology. By reviewing the theoretical foundations and cosmological implications of these entropic frameworks, we aim to clarify the role of
entropy, discuss open issues and outline directions toward a deeper thermodynamic and informational understanding of
gravity and cosmology.
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All authors Emmanuel N. Saridakis, Giuseppe Gaetano Luciano, Andreas Lymperis, Eirini C. Telali
Astrophysics of Galaxies
Investigating the ionization mechanisms powering the extreme emission lines in metal-poor galaxies
C. Daoutis, V. Lebouteiller, D. Schaerer et al. (+11 more)
Extreme emission metal-poor
galaxies (EEMPGs) are excellent local laboratories for understanding the extreme physical conditions and ionizing radiation fields in the early Universe. However, the exact source of high-ionization emission lines in them, whether from intermediate-mass black holes (IMBHs), ultra-luminous X-ray sources (ULXs), or radiative shocks, remains debated. We characterize the fundamental properties and ionizing radiation field on metal-poor EEMPGs, aiming to identify the dominant sources of the highly ionizing
photons that drive these lines. We selected a sample of 11 EEMPGs, among the most metal-poor
galaxies with JWST/MIRI observations known so far (12+log(O/H) < 8.0, or Z/Z$_\odot$ < 20%). Using optical and IR diagnostic diagrams for ions of both high and low ionization potential, we constrain the ionization source dominating their spectral features. We detect high-ionization lines, notably He II$\lambda$4686 in all
galaxies and [Ne V] 14.3 $\mu$m in 42% of a broader sample of local EEMPGs. The multi-wavelength diagnostic diagrams reveal that our EEMPGs are located in areas that normally are occupied by active galactic
nuclei (AGNs) or between the
star-formation and AGN sequences. Evaluating the energetics required to produce these lines, we find that radiative shocks and ULXs are not sufficient. Instead, our analysis suggests that a combination of sources with
star-formation and a small contribution from an IMBH provide enough high-energy
photon budget to explain the emission lines of ions with high-ionization potentials (> 54 eV). Our EEMPG sample, covering various properties, is ideal for studying the first
galaxies. Their flux ratios of low- and high-ionization lines suggest stellar radiation as the likely ionization source, with a small contribution from an IMBH (4-8%). Pure shocks fail to explain the observed emission line ratios and ionizing
photon budget.
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All authors C. Daoutis, V. Lebouteiller, D. Schaerer, I. Morel, O. Bait, S. Satyapal, S. Doan, B. Trahin, A. Gurpide, Y. Izotov, N. Guseva, L. Ramambason, A. Verhamme, SpeXion Team
High Energy Astrophysical Phenomena
A Tentative Line-like GeV Excess in Fermi Blazar 4FGL J1754.2+3212: Implications for Jet Physics and Beyond
Shi-Ju Kang, Yue Yin, Yong-Gang Zheng et al. (+1 more)
We report the detection of a tentative, narrow spectral feature in the GeV gamma-ray spectrum of the blazar 4FGL J1754.2$+$3212, using approximately 16.5 years of observations from the Fermi Large Area
Telescope. A detailed likelihood analysis of the time-averaged spectrum reveals a localized, line-like excess at an energy of $\sim$31 GeV, with a local statistical significance of $\sim$3$\sigma$ (3 degrees of freedom), without corrections for multiple trials and the look-elsewhere effect. This feature is not well described by standard smooth continuum models such as a single log-parabola. The addition of a Gaussian component significantly improves the spectral fit. If confirmed by future observations with higher sensitivity, this feature would represent a novel phenomenon in blazar astrophysics. We explore its potential physical origins, which could involve exotic processes such as dark matter annihilation or
photon-
axion-like-particle oscillations, or extreme astrophysical mechanisms within a structured jet. Regardless of its ultimate nature, this finding highlights the potential of deep spectral studies of blazars to reveal non-standard physics and challenges conventional one-zone emission models. Definitive verification awaits observations by next-generation instruments, particularly the Very Large Area $\gamma$-ray Space
Telescope (VLAST).
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All authors Shi-Ju Kang, Yue Yin, Yong-Gang Zheng, Qingwen Wu
High Energy Astrophysical Phenomena
Study of blazar variability through their flux distribution for CTAO long-term monitoring
A. Mikhno, J. Biteau and J.-P. Lenain on behalf of the CTAO collaboration
The CTAO Key Science Project on Active Galactic
Nuclei (AGN) includes a long-term monitoring (LTM) program of blazars. The probability distribution function (PDF) of the flux extracted from unbiased blazar lightcurves can provide important insight into the physical processes taking place in relativistic jets and their connection to observed variability. The aim of this work is to define an optimal observational strategy for the CTAO LTM program using the flux distributions as a quantitative metric. To achieve this goal, we develop a simulation-based analysis framework that enables a systematic comparison of different observational strategies. Light curves were simulated as would be observed with the future CTAO for a representative set of AGN sources, following four different observational strategies within a fixed time budget. For each simulated light curve, different PDF models were fitted and their goodness of fit was evaluated. Based on the best-fit parameters, Monte Carlo simulations were generated to assess the ability of the method to recover the underlying PDF model. Since the true model used to generate the simulated light curves is known, this procedure allows us to quantify the discriminatory power of the
algorithm and to identify which observational strategy maximizes model discrimination. Additionally, the
algorithm has the potential of discrimination against different models for the flux distributions, such as Gaussian and lognormal. Once validated on simulations, the method is applied to archival lightcurves from existing gamma-ray instruments to extract flux PDFs and study the physical processes driving blazar variability. The analysis framework has been developed and tested on simulated CTAO-like data, showing good stability and robustness. A study to optimize the observing strategy for the CTAO LTM is presented.
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Cosmology and Nongalactic Astrophysics
JWST evidence for a sharp "Cosmic Daybreak" at z = 15
Jiashuo Zhang, Tom Broadhurst, Tzihong Chiueh et al. (+9 more)
Luminous young
galaxies have been uncovered with relative ease by JWST, extending to z=14.5, so it is puzzling that deeper spectroscopy of fainter candidates now finds only interlopers. This
redshift `ìmpasse" is underscored by the measured stellar ages of these high-z
galaxies, which we show converge to zero by z=15, with a marked absence of earlier
star-formation. Taken literally, such a late transition from the Dark Ages to luminous
galaxies is unlike the gradual
Cosmic Dawn of standard LCDM, but does confirm a key prediction of Wave Dark Matter, $\psi$DM, as a Bose-Einstein condensate. The de Broglie wave pressure resists
gravity until a substantial Jeans mass of $4\times 10^9M_\odot$ is overcome at z$=$15, corresponding to a light
boson $m_\psi=2.2_{-0.3}^{+0.4} \times 10^{-22}$eV, and similar to independent estimates from
lensing anomalies and dwarf
galaxies. Furthermore, the substantial luminosities of the highest
redshift galaxies appear to converge to the initial Jeans scale of $\psi$DM, whereas LCDM predictions extend to lower luminosities and larger ages than observed. These contrasting predictions can be definitively tested as JWST observations accumulate, with diametric implications for Dark Matter as heavy particles beyond the Standard Model or ultra-light
bosons motivated by the String Axiverse.
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All authors Jiashuo Zhang, Tom Broadhurst, Tzihong Chiueh, Hsi-Yu Schive, Keiichi Umetsu, Jose M. Diego, Paloma Morilla, Alvaro Pozo, Chian-Chou Chen, Jeremy Lim, Pablo G. Perez-Gonzalez, Rogier Windhorst
High Energy Astrophysical Phenomena
4U 1624-490 as a possible intermediate-mass X-ray binary: constraints from XRISM and NuSTAR spectroscopy
R. Iaria, A. Anitra, T. Di Salvo et al. (+7 more)
High-inclination dipping
neutron-
star X-ray binaries provide a direct view of
accretion-flow structure because the line of sight intercepts ionised
plasma above the disc. We analyse two XRISM/Resolve observations of 4U 1624$-$490 with simultaneous NuSTAR coverage, dividing the data into seven orbital-phase intervals. Phase-resolved fits include neutral partial covering, a photoionised absorber, thermal Comptonisation, and ionised disc reflection. Fe XXV and Fe XXVI absorption are detected over most of the orbit. The absorber column density, ionisation state, covering fraction, and projected velocity vary with orbital phase and the lines are systematically blueshifted, with line-of-sight velocities of about $85$-$440\ {\rm km\,s^{-1}}$. Absorption-only models leave broad Fe-K residuals, while ionised reflection improves the fits. The velocity modulation has a semi-amplitude $K=210\pm14\ {\rm km\,s^{-1}}$ and, if interpreted as orbital motion, implies a mass function $f(M)=0.83\pm0.17\,M_\odot$. Residual structure in the blue wing of Fe XXVI suggests additional kinematic complexity near the dip, but the modulation remains consistent when the two dip-adjacent measurements are excluded. If the absorber traces the
neutron-
star orbital motion, the inferred donor mass is $M_2=2.66\pm0.32\,M_\odot$, compatible with a Roche-lobe-filling B9 V-B9.5 V
star. Under this interpretation, 4U 1624$-$490 may be an intermediate-mass rather than a classical low-mass X-ray binary. (Abridged abstract)
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All authors R. Iaria, A. Anitra, T. Di Salvo, A. Sanna, F. Barra, L. Burderi, C. Maraventano, S. Caserta, W. Leone, C. Miceli
High Energy Astrophysical Phenomena
Radio component of the multi-messenger emission from the anticipated T Coronae Borealis outburst
O. Petruk, T. Kuzyo, S. Orlando et al. (+4 more)
T Coronae Borealis is the nearest symbiotic recurrent nova and is expected to undergo a new eruption soon, offering a rare opportunity to study shock
evolution and particle acceleration. We predict
radio emission from the outburst and assess how
radio observations can constrain the circumbinary medium (CBM) and
cosmic-ray acceleration. We post-process three-dimensional (3D) hydrodynamic nova simulations with a multi-zone model for particle acceleration and
radio emission, computing thermal free-free and non-thermal synchrotron radiation, including the Razin effect and free-free and synchrotron self-absorption for different CBM configurations. Early
radio morphology should not be interpreted directly as the intrinsic shock geometry, because free-free absorption selectively obscures regions of the 3D emitting volume. The intrinsic
radio emission is dominated by synchrotron radiation from electrons accelerated at the forward shock, with unabsorbed fluxes reaching 100-1000 Jy at GHz frequencies during the first day. Dense ejecta and shocked CBM material strongly absorb the emission, reducing the observable flux by several orders of magnitude. The source becomes largely transparent at GHz frequencies within about one month.
Radio emission remains predominantly non-thermal during the first year, while thermal emission becomes important only for dense equatorial enhancements. The
radio spectral index evolves from positive values caused by absorption to the optically thin synchrotron value of about 0.5 after several weeks. A short-lived polarized signal may arise during the first few days if the red giant's
magnetic field contributes to the
cosmic-ray-generated field. Early multi-frequency
radio monitoring and polarimetry of the forthcoming T CrB eruption will probe density structure and
magnetic field, testing particle acceleration in symbiotic recurrent novae.
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All authors O. Petruk, T. Kuzyo, S. Orlando, L. Chomiuk, F. Bocchino, M. Miceli, V. Beshley
Earth and Planetary Astrophysics
The dust in Sauron's eye - Observational and experimental results on the debris disk around HR 4796
M. Bonduelle, J. Milli, O. Poch et al. (+14 more)
The optical properties (scattering phase function SPF; degree of linear polarization DoLP; reflectance) of the dust particles orbiting in debris disks can be retrieved through scattered light imaging and are linked to the physicochemical properties of the dust (size, shape, composition...). Among debris disks, the bright, narrow disk surrounding HR 4796A presents several peculiarities, in particular unusually high DoLP values at small scattering angles. We aim at improving the constraints on the properties of the dust particles orbiting in HR 4796. We use new observational data (SPHERE/ZIMPOL and IRDIS) in scattered light of HR 4796, for lambda = 0.63 um; 0.79 um and 1.25 um. We modeled the disk at each of these wavelengths and found
geometric parameters consistent with previous results. We obtained the parametrized SPF and DoLP over the whole range of scattering angles (13 degrees to 167 degrees) and extracted the DoLP and spectral reflectance at 90 degrees (without any parametrization) from the visible to the NIR wavelength range. We compared the reflectance and polarimetric properties of HR 4796 to those measured on a laboratory dust sample and find that the sample providing the best match appears to be large iron sulfides particles. We confirm that the DoLP of HR 4796 peaks at high values (> 45 percent) and for small scattering angles (< 55 degrees). At a 90 degrees scattering angle, we observe a red spectral slope in the visible and NIR wavelength range, as well as a blue polarimetric slope. These results are compatible with large (a few um to 100 um) absorbents being the main scatterers in the disk. We show that the DoLP of HR 4796 is notably different from that of Solar System comets and seems closer to that of some more processed near-Earth orbit asteroids, possibly indicating devolatilization and/or melting induced by space weathering on the dust particles of HR 4796.
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All authors M. Bonduelle, J. Milli, O. Poch, N. Engler, M. Rigouleau, R. Tazaki, J. Ma, J. Olofsson, J-B. Renard, J. Lasue, R. Sultana, G. Duchêne, L. Martinien, M. Roumesy, C.H. Chen, C. Lisse, J-C. Augereau
High Energy Astrophysical Phenomena
Gamma-ray emission toward supergiant shells in the Large Magellanic Cloud
Qixin Yu, Olaf Reimer and Anita Reimer
The Large Magellanic Cloud (LMC), a satellite
galaxy of our Milky Way, is considered to be a very good target for investigations of diffuse gamma-ray emission. Observations have shown that diffuse emissions are related to the large- and small-scale structures of the LMC. Particularly, it has been suggested that some of the small-scale bright diffuse emissions coincide with supergiant shells (SGSs) previously identified based on H$\alpha$ images. We analyzed the gamma-ray emission from the LMC using more than 15 years of observations with the Fermi Large Area
Telescope in the energy range of 300$\,$MeV-300$\,$GeV. A dedicated spatial and spectral analysis was made for diffuse emission components of the LMC. Particularly, we evaluated the emissions from SGSs in detail using phenomenological approaches, and we established their corresponding spatial templates for gamma-ray emission. In the analysis of small-scale extended emissions, we detected seven H$\alpha$-selected SGSs at a significance of more than $5\sigma$. The emission structure nested inside the SGSs appears to be a non-Gaussian feature and is very likely due to a modulated
cosmic-ray distribution by an ensemble of
supernova remnant shocks. The spectra of the gamma-ray emission for most SGS regions favor a hadronic origin. For the large-scale diffuse emission from the LMC disk, our results suggest an interplay of
hadron- and lepton-induced emission. The
cosmic-ray
proton energy density derived for bright SGSs is 3-10 times higher than that in the LMC disk. SGS$\,2$ was detected to be the most significant emission region among all SGSs. Based on the gamma-ray excess emission we detected in H$\alpha$-selected SGSs in the LMC, we estimate that their contribution to the total diffuse gamma-ray emission in the LMC is at a non-negligible 41% level.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th
The compressible liquid drop model with curvature included algebraically for the pasta phases in neutron stars
Dmitry Kobyakov
In the compressible
liquid drop model (CLDM), the
curvature energy term has been included in many works in the literature, and its effects on the presence of pasta phases have also been extensively investigated. However, the analytical part of the inclusion used to cease once a 4-order algebraic equation for the optimized size of the
nucleus was written. In this paper, an optimization is suggested to the analytical part of the solution of the CLDM equations. Solving analytically the 4-order algebraic equation proves to be helpful for a straightforward identification of the denied parameter ranges in which the CLDM has no real-root solutions. Using a particular nuclear force derived from the chiral effective field theory, I investigate effects on the ground state of the
nucleus curvature. Surprisingly, the inclusion has lead to a significant modification of the range of baryon density in which the bubble phases are found, disfavoring the bubble phases from the ground state. This shows a strong difference between the predictions of the CLDM with the
nucleus size obtained when including the
curvature term and that obtained from the $w_\mathrm{s} = 2w_{\mathrm{C+L}}$ approximation. The importance of the
curvature energy in the CLDM is linked with its ability to change qualitatively the ground state. This paper presents an analytical extension to the CLDM solution, which is ready to be used with any other nuclear model in the future, in order to optimize the inclusion of the nuclear
curvature energy, and is not limited to one nuclear model.
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