Solar and Stellar Astrophysics
Teleparallel torsion and white dwarf structure in \(f(T)=T+\Xi T^2\) gravity
Edson Otoniel, Jonathan A. Reboucas and Iarley P. Lobo
We investigate how quadratic torsion modifies the
equilibrium structure of white dwarfs in covariant $f(T)=T+\Xi T^2$
gravity. Static spherical configurations are calculated with a fixed equation of state for cold carbon matter, including relativistic electron degeneracy and Coulomb
lattice corrections. The stellar interior is matched to a
vacuum exterior, and the mass is determined from the asymptotic geometry. At fixed central density, negative couplings produce more massive and more compact configurations than general relativity, whereas positive couplings give smaller masses and larger radii. The deviations increase with central density and are more pronounced in mass than in radius. The first limiting feature of each sequence depends on the coupling. For $\Xi=-10^{18}\,\mathrm{cm}^{2}$, the sequence remains monotonic up to the electron capture density and reaches $1.508\,M_\odot$. General relativity and $\Xi=+10^{18}\,\mathrm{cm}^{2}$ instead reach mass turning points at $1.385\,M_\odot$ and $1.366\,M_\odot$, respectively. The positive extreme can be continued as an
equilibrium solution to the capture density, where its mass decreases to $1.24\,M_\odot$, but this configuration lies beyond the turning point and is not the maximum mass along that sequence. These results identify a density dependent structural response to torsion that changes the stellar mass scale without modifying the matter equation of state.
Read the full abstract ▾
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Theoretical Aspects of Direct Waves in Kerr Black Holes: Pole-Splitting Method for Ringdown Analysis
Nao Nakamoto, Naritaka Oshita and Hiroki Takeda
We formulate the theoretical aspects of direct waves (DWs) in the case of extreme-mass merger. A DW is a source-driven waveform characterized by a complex frequency $\omega_{\rm G}$, which reflects the orbital motion of the particle in the vicinity of the black hole, including a part of the orbit inside the ergoregion: its real part is governed by frame dragging and its imaginary part by the
redshift of the source. Using the Green's function technique, we derive the source-driven frequency $\omega_{\rm G}$, describe its screening by the potential barrier, and discuss its relation to dynamically excited quasinormal modes (QNMs). We then introduce a pole-splitting method that divides the full waveform into a QNM-pole sector and a non-QNM sector. Unlike QNM filtering, which multiplies the waveform spectrum by a filter function and thereby deforms it through a frequency-dependent time shift (i.e., group delay), our pole-splitting method merely divides the transfer function into pole and non-pole parts, separating the full waveform. Simulating a quasi-circular plunge into a Kerr black hole with medium and rapid
spins, we find that the frequency and decay rate of the non-pole sector in the dominant mode, $\ell = m = 2$, evolve consistently with $\omega_{\rm G}$-or with its screened counterpart $\omega_{\rm screen}$-establishing the DW as a probe of the ergoregion and of the
redshift effect around a black hole.
Read the full abstract ▾
Cosmology and Nongalactic Astrophysics
A Multi-Axion Ladder Across Cosmic History: From Inflation, BBN, and Early Dark Energy to Late-Time Accelerated Expansion
Amartya Sengupta, Dejan Stojkovic and Adam G. Riess
What if dark energy is recurrent throughout
cosmic history? In this picture, episodes of scalar-field dark energy become less surprising and more natural features of
cosmic evolution. We construct a homogeneous multi-
axion cosmology with a transient contribution during Big Bang nucleosynthesis, two early dark energy components before recombination, and a thawing field that supplies the present dark-energy density. As Hubble friction weakens, the fields begin to roll at successive epochs set by their potential-
curvature scales. Their initial displacements affect the rolling delays and peak energy fractions. The transient fields have third-power cosine potentials, whose sextic minima allow faster-than-radiation dilution during rapid, small-amplitude oscillations. All four fields are evolved in a common Friedmann background, with their first roll and subsequent dynamics resolved numerically. With reference matter and radiation densities taken from Planck 2018, the
benchmark has a nucleosynthesis-era peak fraction of approximately $0.99\%$ near $z=10^9$. The two early dark energy fields peak near $z=7.9\times10^3$ and $2.4\times10^3$, with individual fractions of $8.6\%$ and $7.8\%$; their combined fraction reaches $9.7\%$. The late-time field is normalized to supply a present fraction of approximately $0.685$, while the three transients leave a combined fraction of approximately $6.0\times10^{-7}$. An aligned two-
axion example illustrates the enhanced field range available for an inflationary extension. We also outline how searches for transient contributions to the expansion rate at other epochs could constrain additional
axion scales.
Read the full abstract ▾
Cosmology and Nongalactic Astrophysics
Reconstructing Early Primordial Black Hole Domination from Gravitational-Wave Backgrounds
Daniel del-Corral and Angus Spalding
Primordial Black Holes (PBHs) with masses below $\mathcal{O}(10^9)$g occupy an interesting region of parameter space that is largely inaccessible to conventional observations. Despite evaporating before Big Bang Nucleosynthesis (BBN), these PBHs can naturally generate a period of early matter domination in the early Universe. A primordial gravitational-wave background (GWB) provides a window onto this otherwise inaccessible regime, since the modified expansion history leaves a characteristic spectral feature associated with the onset and end of PBH domination. The locations of these characteristic frequencies can be used to reconstruct the underlying PBH parameters, in particular the PBH mass. For a freely propagating GWB, the location of these frequencies additionally allow the initial PBH abundance to be determined. We derive simple numerical relations that map these characteristic frequencies directly onto the PBH mass and initial abundance. Future GW experiments span a vast frequency range, providing sensitivity to PBH masses from the BBN bound of $\mathcal{O}(10^9)\,\mathrm{g}$ down to the lower bound of $\mathcal{O}(10)\,\mathrm{g}$. We find that the nanohertz signal reported by NANOGrav, if primordial in origin, is already probing PBH masses in the range $4$–$90\,\mathrm{Mg}$. GW observations therefore offer access to a vast region of PBH parameter space that is otherwise beyond the reach of current experiments.
Read the full abstract ▾
High Energy Astrophysical Phenomena
Hierarchical Population Inference with Normalizing Flows for Binary Black Holes
Leonardo Iampieri and Simone Mastrogiovanni
Low-dimensional parametric mass models are standard in gravitational-wave population inference, but their rigidity can bias the recovered distribution and the conclusions drawn from it. We present a pipeline in which the source-frame binary-black-hole population in $(z,m_1,m_2)$ is represented by a normalizing flow trained directly through the hierarchical likelihood, with event posterior samples propagating measurement uncertainty and detected injections accounting for selection effects. We restrict population statements to the region supported by the injection campaign; conditioning on this region can itself induce an apparent association between mass and
redshift. We therefore introduce a mutual-information diagnostic that compares the reconstruction with a
redshift-independent reference under the same support restriction, testing for dependence beyond that induced by the support geometry. We validate the method on two simulated catalogues differing only in whether the characteristic primary-mass scale evolves with
redshift. The reconstruction recovers the injected mass structure in both, and the
benchmarks establish how the diagnostic behaves in the presence and absence of intrinsic
evolution. Applied to the GWTC-5.0 catalogue, the method recovers features near $10\,M_\odot$ and $35\,M_\odot$, consistent with the LVK population analysis of the same catalogue, and finds no evidence for intrinsic
evolution of the primary-mass spectrum with
redshift. More broadly, the pipeline addresses a problem common to many observational sciences: recovering a population distribution from noisy, indirect, and selection-biased measurements of its members.
Read the full abstract ▾
Astrophysics of Galaxies
Learning JWST. I. A Foundation Model for New Population Discoveries and Morphology-Aware Photometric Redshift Measurements in the JADES Survey
Jiani Ding, Minghao Yue, Yongda Zhu et al. (+2 more)
We present FM-JADES-v1, a self-supervised foundation model for James Webb Space
Telescope (JWST) deep-field science, trained with 482,444 objects from the JWST Advanced Deep Extragalactic Survey (JADES) Data Release 5 using multi-band imaging and the photometric catalog. The shared
embedding space is trained without class labels. We demonstrate that FM-JADES-v1 can serve as a powerful tool for object discovery and improving property measurements using two experiments, blind active discovery and few-band photometric
redshift. For blind object discovery, FM-JADES-v1 identifies rare object populations such as high-
redshift galaxies and Little Red Dots (LRDs) without any prior population labels or population-specific selection criteria. These rare populations emerge as isolated islands in the
embedding space, which can be identified without prior astrophysical knowledge. For few-band photometric
redshift, FM-JADES-v1's learned
embeddings achieve $\sigma_{\rm NMAD}=0.157$ in a strictly controlled three-band (F115W/F200W/F356W) photo-$z$
benchmark, compared to $\sigma_{\rm NMAD}= 0.44$ for template fitting. These results demonstrate the potential of self-supervised multi-modal representations as scalable discovery spaces for large astronomical surveys. Applied to ongoing and future wide-field surveys from JWST, Roman, Euclid, and Rubin/LSST, this framework could enable systematic searches for rare populations, as well as enabling multiple downstream tasks such as improving astrophysical property measurements.
Read the full abstract ▾
All authors Jiani Ding, Minghao Yue, Yongda Zhu, Xiaohui Fan, Yufeng Luo
Solar and Stellar Astrophysics
A Homogenized Catalogue of Variable Stars in the Globular Cluster M22: Membership, Physical Parameters, and Distance
M. A. Yepez, B. Moreno-Amaro, M. Ornelas-Castañeda et al. (+2 more)
We present a photometric analysis of the variable
stars in the field of the globular cluster M22 (NGC 6656), using time-series photometry from the literature and from OGLE and Gaia-DR3 data. From a sample of 666 variable
stars in the field, we identify 94 as cluster members, including 10 RRab, 17 RRc, 2 Type II Cepheids, 15 SX Phe, 15 SR
stars and 22 eclipsing binaries. Fourteen of these members are not included in the Catalogue of Variable
Stars in Globular Clusters. Through the
Fourier decomposition of the RR Lyrae light curves, we derived $[\mathrm{Fe/H}] = -1.73 \pm 0.17$ dex and $d = 3.27 \pm 0.14$ kpc. Among the RRc
stars, V15 shows an additional frequency with a frequency ratio $f_{0.61}/f_\mathrm{1O} = 0.6152$, consistent with the RR$_{0.61}$ phenomenon. Using P-L relations for member SX Phe
stars, we obtained $d = 3.31 \pm 0.17$ kpc, consistent with the RR Lyrae distance. We constructed a CMD comprising only cluster members, which allows us to confirm the evolutionary status of the cluster's RR Lyrae
stars. None of the fitted isochrones satisfactorily reproduces the CMD morphology, which is consistent with the presence of multiple stellar populations in M22.
Read the full abstract ▾
All authors M. A. Yepez, B. Moreno-Amaro, M. Ornelas-Castañeda, A. Arellano Ferro, D. Deras
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Solar Neutrino Constraints on Inelastic Dark Matter Scattering in Light of Recent LUX-ZEPLIN Observations
Thong T.Q. Nguyen, Tim Linden and Dan Hooper
The LUX-ZEPLIN (LZ) Collaboration recently reported the detection of a single nuclear recoil candidate event with a very high recoil energy. The lack of any corresponding low-energy events motivates models in which dark matter scattering with
nuclei has a nontrivial momentum dependence or proceeds inelastically, suppressing the rate of low-energy recoils. In this study, we consider the constraints on inelastic dark matter, including scenarios favored by the LZ event, from the absence of an excess of high-energy
neutrinos from the Sun in IceCube observations. We confirm the results of Pospelov & Ramani and show, more generally, that the lack of an excess of high-energy
neutrinos from the Sun strongly constrains the parameter space in this class of models.
Read the full abstract ▾
Solar and Stellar Astrophysics
The Dyn-Atmo Survey: JWST/NIRSpec spectroscopy of dynamical benchmark GJ 758 B
Alexander Madurowicz, Emily Rickman, Daniella Bardalez Gagliuffi et al. (+22 more)
We present new JWST/NIRSpec IFU high contrast spectroscopic observations of the brown dwarf companion GJ 758 B. Extensive radial velocity monitoring of the primary has enabled high-precision measurements of the companion mass through characterization of their joint orbital dynamics. The combination of prior space- and ground-based photometry and spectroscopic observations in concert with a spectral model-independent mass makes this target an ideal
benchmark for calibrating evolutionary models with known mass-age-luminosity degeneracies. A template-matching analysis on the NIRSpec/IFU data (F290LP,G395H; $\lambda \in$ [2.87-5.27] $\mu$m) detects the companion at the expected orbital position with incredible significance (265.2$\sigma$). Comprehensive spectral analysis including published
datasets over a variety of different spectral model families reveal that an inference using a uniform radius prior is plagued by inaccurate posteriors. The atmospheric model degeneracy between
metallicity,
gravity, and clouds pull the inferred mass/
gravity/radius to an unphysical portion of parameter space for all model families tested. A constrained inference with a gaussian prior on the mass can mitigate this issue but models without clouds still struggle to accurately reproduce the K-band photometry and result in mass inferences which are inconsistent with the dynamics. We explore modifying the spectral models with custom post-processed clouds and molecular abundance perturbations of ammonia and hydrogen sulfide. We find the best-fitting model includes clouds with no patchiness (hole fraction f$_\mathrm{hole}$ = 0), a small fractional depletion in ammonia and moderate enhancement in hydrogen sulfide.
Read the full abstract ▾
All authors Alexander Madurowicz, Emily Rickman, Daniella Bardalez Gagliuffi, James Mang, Kim Ward-Duong, William O. Balmer, Brendan P. Bowler, Emily Calamari, Henry Dennen, Jacqueline K Faherty, Kyle Franson, Mark R. Giovinazzi, Lisseth Gonzales Quevedo, Kielan K. W. Hoch, Piper Lentz, Elena Manjavacas, Klara Matuszewska, Ashley Messier, Caroline V. Morley, Evert Nasedkin, Marshall Perrin, Laurent Pueyo, Jean-Baptiste Ruffio, Christopher A. Theissen, Jerry W. Xuan
Solar and Stellar Astrophysics
The Dyn-Atmo Survey: High-contrast Imaging Spectroscopy of the Substellar Companion HD 13724 B with the JWST NIRSpec IFU
Kielan K. W. Hoch, Alex Madurowicz, Evert Nasedkin et al. (+22 more)
We present the first spectral analysis from the JWST Cycle 3 GO Program #6362, the Dyn-Atmo Survey of dynamical-atmospheric
benchmarks, characterizing the atmospheres of directly-imaged companions with dynamical masses and measured orbits. This program has obtained moderate-resolution spectra (R$\sim$2700, 3-5$\mu$m) using the NIRSpec/G395H IFU. We observe the T4-dwarf companion, HD 13724 B, companion to a G-type
star at a projected angular separation of 0”2. Updated orbital monitoring constrains the mass to $38.3\pm0.6~M_{\rm{Jup}}$, which we use as a Gaussian prior when inferring the atmospheric state. We fit the continuum-subtracted spectrum using the BT-SETTL, Sonora Diamondback, Sonora Flame Skimmer, and NEWERA-PHOENIX self-consistent model grids, together with petitRADTRANS atmospheric
retrievals. We adopt bulk parameter values of $T_\mathrm{eff}$=$1150\pm$195 K, $\log g$=5.1$\pm0.3$ dex, [M/H]=0.4$\pm$0.4, $\log_{10}(K_{zz})$=6.33$_{-2.22}^{+2.59}$, and C/O=$0.50\pm0.13$ using a
bayesian average across model grids. We find degeneracies in the models between surface
gravity,
metallicity, and $K_{zz}$ for Sonora Diamondback and Flame Skimmer. The Flame Skimmer and NEWERA-PHOENIX vertical mixing strengths are incompatible, with Flame Skimmer finding a systematically lower value. The
retrievals favor an atmosphere in chemical
equilibrium, with enhanced
metallicity and a solar C/O ratio, but with no detection of disequilibrium chemistry, and no detection of trace gases other than CH$_4$, CO$_{2}$, $^{12}$CO and H$_{2}$O. Ultimately, we identify critical challenges in forward modeling continuum-subtracted G395H spectra in the low signal-to-noise regime. We find that including independent dynamical mass measurements better constrains atmospheric parameters, but degeneracies between self-consistent model parameters limit accurate atmospheric parameter inferences.
Read the full abstract ▾
All authors Kielan K. W. Hoch, Alex Madurowicz, Evert Nasedkin, Emily Rickman, Daniella C. Bardalez Gagliuffi, James Mang, Caroline V. Morley, Christopher A. Theissen, William O. Balmer, Brendan P. Bowler, Emily Calamari, Henry Dennen, Jacqueline K. Faherty, Kyle Franson, Mark R. Giovinazzi, Lisseth Gonzales Quevedo, Elena Manjavacas, Piper Lentz, Klara Matuszewska, Ashley Messier, Marshall Perrin, Laurent Pueyo, Jean-Baptiste Ruffio, Kimberly Ward-Duong, Jerry W. Xuan
Earth and Planetary Astrophysics
Planetary Accretion Is Less Frequent in Wide Binaries: Evidence from Metal-Enriched White Dwarfs in DESI DR1
Siyi Xu, Laura. K. Rogers, Joan Najita et al. (+32 more)
Binary
stars are common in the
Galaxy, and understanding how stellar binarity influences the formation and
evolution of planetary systems is an active area of research. In this study, we use metal-enriched white dwarfs in wide binaries as tracers of long-lived planetary systems. With Data Release 1 from the Dark Energy Spectroscopic Instrument (DESI), we find that the fraction of cool metal-enriched white dwarfs in wide binaries is 9.8\,$\pm$\,2.1%, significantly lower (4.7\,$\sigma$) than the 20.5\,$\pm$\,0.9% in a control sample of single systems. Furthermore, we identify a tentative dependence of metal enrichment on projected separation and white dwarf effective temperature, where enrichment fraction decreases at smaller separations and lower temperatures. These findings indicate that, compared to single
stars, binary systems either start with smaller initial planetary reservoirs due to suppressed planetesimal formation or undergo more rapid depletion of planetary material during the initial part of the white dwarf stage.
Read the full abstract ▾
All authors Siyi Xu, Laura. K. Rogers, Joan Najita, Boris T. Gänsicke, Paula Izquierdo, Sergey E. Koposov, Christopher J. Manser, Andrew Swan, Sandford Nathan, Wang Wenting, J. Aguilar, S. Ahlen, C. Allende Prieto, D. Bianchi, D. Brooks, T. Claybaugh, A. de la Macorra, J. E. Forero-Romero, Satya Gontcho A Gontcho, G. Gutierrez, R. Joyce, M. Landriau, L. Le Guillou, A. Meisner, R. Miquel, W. J. Percival, F. Prada, I. Pérez-Ràfols, G. Rossi, E. Sanchez, D. Schlegel, J. Silber, G. Tarlé, B. A. Weaver, R. Zhou
High Energy Astrophysical Phenomena
Spectral evolution of NS binary system GX 349+2 using AstroSat observations
Garima Tyagi, Suchismito Chattopadhyay, Sree Bhattacherjee et al. (+3 more)
We present a broadband spectral study of the Sco-like Z source GX 349+2 using AstroSat LAXPC and SXT observations obtained during 2019 and 2024. The X-ray light curves exhibit large variability, and the hardness-intensity diagram traces the characteristic Z-shaped track. Using hardness ratio and intensity, the Z-track is segmented into six regions comprising normal branch, soft apex, and an extended flaring branch. We perform simultaneous broadband spectral fitting in the energy range 0.7-25.0 keV using two model configurations, tbabs*(thcomp*bbodyrad+diskbb) and tbabs*(bbodyrad+thcomp*diskbb), to study the
evolution of emission from the
neutron-
star boundary layer,
accretion disk, and Comptonizing corona along the Z-track. The comparative analysis reveals that, irrespective of the adopted Comptonization geometry, the inferred inner disk radius remains large (~100 km) and exhibits no systematic inward motion as the source luminosity increases. This suggests that the
accretion disk remains truncated and the disk luminosity tends to saturate, consistent with a radiation pressure influenced inner disk. The relatively small variation in the inferred mass
accretion rate across the branches indicates that changes in $\dot{M}$ alone cannot account for the observed Z-track
evolution. Instead, the boundary-layer component becomes progressively dominant toward the flaring branch, with both its temperature and flux increasing with total luminosity, while the relative contribution from the disk decreases. These results indicate a redistribution of
accretion power toward the boundary layer and the associated Comptonizing region, suggesting that the primary energy dissipation in GX 349+2 occurs within the boundary layer region of the
neutron star.
Read the full abstract ▾
All authors Garima Tyagi, Suchismito Chattopadhyay, Sree Bhattacherjee, Akash Garg, Ranjeev Misra, Somasri Sen
High Energy Astrophysical Phenomena
Relativistic Magnetohydrodynamics from Myers-Pospelov Lorentz-Violating Electrodynamics
Matheus Duarte and Vitor de Souza
We derive the equations of relativistic magnetohydrodynamics from Lorentz-violating Myers-Pospelov electrodynamics. Starting from the modified fermionic and electromagnetic equations of motion, we employ the covariant Wigner formalism to establish the semiclassical spectral constraints and distribution function, which, combined with Noether's
theorem, yield the energy-momentum tensor, particle current, and corresponding conservation laws in the presence of Lorentz violation. The resulting hydrodynamic description contains Lorentz-violating corrections to the thermodynamic quantities and to the fluid currents. In the purely timelike sector, these corrections can be absorbed into effective thermodynamic quantities, preserving the isotropic structure of the fluid equations. In contrast, spacelike backgrounds introduce explicit contributions along the preferred direction, which cannot be absorbed into the standard hydrodynamic variables and give rise to anisotropic forces and torques. These effects lead to departures from standard relativistic magnetohydrodynamics and provide a direct macroscopic manifestation of the Lorentz-violating background. Our results provide a first-principles derivation of Lorentz-violating relativistic magnetohydrodynamics and establish a framework for investigating the macroscopic consequences of Lorentz violation in magnetized relativistic fluids.
Read the full abstract ▾
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Might the radiation era extend back to the Big Bang? On dark matter production and the relic graviton background in quadratic gravity
Latham Boyle, Neil Turok and Vatsalya Vaibhav
Naive estimates based on Einstein
gravity with Lagrangian $\frac{1}{2}M_{pl}^{2}(R-2\Lambda)$ suggest that, if the radiation era extended back to the Big Bang (i.e., as far back as the classical spacetime background makes sense), this would result in an over-production of dark matter and a relic
cosmic background of thermal gravitons. Here we revisit these conclusions in quadratic
gravity, the minimal renormalizable completion of Einstein
gravity, whose Lagrangian also includes the terms $\frac{1}{6}f_0^{-2}R^2-\frac{1}{2}f_{2}^{-2}C^{2}$. Assuming the radiation era does extend back to the bang, we find a novel relation between the coefficient $f_{2}$ and the dark matter mass $m_{dm}$, needed to obtain the correct dark matter abundance. This yields a new gravitational production mechanism for dark matter (e.g., stable right-handed
neutrinos). Moreover, the presence or absence of the relic graviton background (detectable by forthcoming CMB experiments via its small imprint on $N_{{\rm eff}}$) will place new constraints on $f_{0}, f_{2}$.
Read the full abstract ▾
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Nuclear-physics-guided Gaussian Processes
Javier Rozalén Sarmiento, Hristijan Kochankovski, Arnau Rios et al. (+1 more)
Gaussian Process Regression is a powerful nonparametric
Bayesian method that provides both predictions and principled uncertainty estimates in closed form. The majority of past applications have relied on agnostic priors, but physics knowledge can be systematically encoded into Gaussian Processes through physically-motivated mean functions and kernels. We exploit this capability in the context of nuclear physics, applying physics-guided Gaussian Process Regression to three problems: nucleon-nucleon scattering phase shifts, mass excesses, and the finite-temperature equation of state of dense matter. In each case, we demonstrate that encoding known theoretical structures yields substantial and systematic improvements in interpolation accuracy, uncertainty calibration, and extrapolation reliability over agnostic baselines. Our results highlight that the design of the prior, and in particular the mean function, is key for obtaining a reliable and well-calibrated Gaussian Process Regression.
Read the full abstract ▾
All authors Javier Rozalén Sarmiento, Hristijan Kochankovski, Arnau Rios, Àngels Ramos
Instrumentation and Methods for Astrophysics
Bayesian Superiority in On/Off analysis
Gleb Babenov and Petr Satunin
We present a detailed comparison of
Bayesian criteria with three non-informative priors - flat, Jeffreys, and scale-invariant - for testing a signal against an unknown background and compare them with the classical frequentist Li-Ma approach in the On/Off problem. We perform Monte Carlo simulations for various background levels and evaluate the Li-Ma and
Bayesian criteria by their Type I error rates. We then simulate a nonzero signal and compare the criteria in terms of Type II error rates. We find that both the Li-Ma criterion and the
Bayesian criterion with the Jeffreys prior control Type I error well, excluding the case of small background $b < 0.5$; the
Bayesian criterion with the Jeffreys prior is statistically more powerful than the Li-Ma criterion for $b \lesssim 40$.
Read the full abstract ▾
Instrumentation and Methods for Astrophysics
The Balloon-borne VLBI Experiment (BVEX) Radio Telescope and Position Tracking System
Felix M. Thiel, Mayukh Bagchi, Laura M. Fissel et al. (+17 more)
Very Long Baseline Interferometry (VLBI) is a technique in
radio astronomy that vastly increases the diffraction limited angular resolution of
radio observations by correlating simultaneous observations of
radio telescopes separated by thousands of kilometers. Ground-based high-frequency VLBI is limited in baseline length by the diameter of the Earth and in sensitivity by molecular absorption of the Earth's atmosphere. One of the ways to improve VLBI is with balloon
telescopes, which are much cheaper than space VLBI
telescopes. In addition balloon-VLBI stations could also improve image quality due to increased uv-coverage. As a first step to achieving VLBI from a balloon-borne platform we present the Balloon-borne VLBI Experiment (BVEX). This is a novel, first-generation balloon-borne VLBI station observing at K-band (22 GHz) which launched as part of the Canadian Space Agency (CSA) STRATOS campaign from Timmins, Ontario, Canada in August 2025, with the aim to demonstrate VLBI from a balloon-borne platform by correlating with a large ground based
telescope. We discuss the design of the 36 inch (91 cm)
radio telescope and receiver with a 2 GHz bandwidth built from commercial-off-the-shelf (COTS) components as well as the
telescope pointing system capable of interfacing with the CSA's CARMENCITA gondola. We also present a novel high precision position tracking system built from COTS components giving <1 mm precision on 1 s time scales which is required for achieving phase tracking at 22 GHz. We further show on-the-ground testing results from the 2025 Timmins campaign. The 2025 flight from Timmins was not successful due to a leak in the balloon preventing the payload from reaching its target altitude where accurate gondola pointing is possible. We therefore wrap up by presenting plans to upgrade the
telescope for a potential next flight opportunity from Palmas, Tocantins, Brazil in 2027.
Read the full abstract ▾
All authors Felix M. Thiel, Mayukh Bagchi, Laura M. Fissel, Aarchi Shah, Lindy Blackburn, Emily Butler, Rafael Costa, Thomas Emo, Vincent L. Fish, Daryl Haggard, Michael D. Johnson, Jessica Lo, Maggie Oxford, Dominic W. Pesce, Ganesh Rajagopalan, Javier L. Romualdez, Adrian K. Sinclair, Bonnie Slocombe, Stephanie St-Jean, Terry Yang
Astrophysics of Galaxies
The atomic multiphase interstellar medium of galaxies in the COLIBRE simulations
Moa Huppenkothen, Sylvia Ploeckinger, Joop Schaye et al. (+7 more)
We analyse the neutral ISM of
galaxies at
redshift z=0 in the COLIBRE hydrodynamical simulations and investigate the conditions under which these two gas phases coexist in a narrow range of thermal pressures. COLIBRE
galaxies are selected based on the
metallicity of their ISM. The median and mass-weighted distributions of thermal pressures of the multiphase ISM are analysed and compared to thermal
equilibrium models and observations. The ISM in
galaxies with gas
metallicities similar to solar values exhibits a clear multiphase structure with a warm and cold phase coexisting in a certain range of thermal pressures. The pressures at which the ISM is multiphase depend on the gas
metallicity. For COLIBRE
galaxies with lower
metallicities ($Z_{\mathrm{ISM}}\lesssim0.1\,\mathrm{Z}_{\odot}$), this multiphase structure largely disappears, partly due to resolution. The thermal pressures weighted by the HI mass of the neutral phases in COLIBRE
galaxies are lower than, but still comparable to, some theoretical works and observational estimates. The thermal pressures show a strong dependence on the weighting scheme. If weighted by the
star formation rate or CI mass, the thermal pressures of the cold phase match those derived from observations. The resulting pressures depend on a combination of the assumed radiation field strength, dust abundance, limited resolution and the weighting scheme. The strong dependence of the thermal pressures on the weighting scheme indicates observational tracers used to estimate the thermal pressure are biased towards high-pressure regions.
Read the full abstract ▾
All authors Moa Huppenkothen, Sylvia Ploeckinger, Joop Schaye, Alejandro Benítez-Llambay, Evgenii Chaikin, Filip Huško, Alexander J. Richings, James W. Trayford, Alvaro Hacar, Juan D. Soler
Cosmology and Nongalactic Astrophysics
TDCOSMO XXXI: New techniques in line-of-sight studies of time delay lenses
Daniel Johnson, Devon Williams, Chris Fassnacht et al. (+5 more)
The distribution of matter along the same line of sight but external to the main lens, quantified by $\kappa_\mathrm{ext}$, is a key source of uncertainty in time delay cosmography and other applications of strong
lensing, and must be independently estimated to avoid biasing the inferred value of the Hubble constant ($H_0$). We present advancements and standardisations in the weighted number counts techniques used to constrain $\kappa_\mathrm{ext}$, in particular the use of the Euclid Flagship Simulation and a breakdown of the line-of-sight contributions between the observer, lens and source. As part of the TDCOSMO 2026 milestone analysis, we apply this updated method to the sample of 11 time delay lenses used in that study. Our estimates for certain systems are sensitive to these methodological changes, but are nonetheless consistent within $1\sigma$ for all but one of the systems which had been studied previously, with the median $\kappa_\mathrm{ext}$ across those systems changing from $-0.002$ to $-0.006$ following this new analysis. This work represents the first estimate of $\kappa_\mathrm{ext}$ values which includes the contribution of the observer-lens and lens-source terms, and largest standardised analysis of time delay lens environments to date.
Read the full abstract ▾
All authors Daniel Johnson, Devon Williams, Chris Fassnacht, Patrick Wells, Pierre Fleury, Allan Schweinfurth, Martin Millon, Aymeric Galan
High Energy Astrophysical Phenomena
One Precessing Jet Pair, Diverse Core-Collapse Supernova Remnant Morphologies
Jessica Braudo and Noam Soker
We produce a diverse set of observed core-collapse
supernova (CCSN)-type morphologies using a precessing pair of opposite jets within the jittering-jets explosion mechanism (JJEM) framework. We conduct a three-dimensional hydrodynamical simulation of a precessing pair of jets that explode a massive
star, and find that a single precessing pair of opposite jets can generate S-shaped structures, pipe-spout-blowout features as observed in the Cygnus Loop, multiple apparent pairs of opposite protrusions similar to some morphological features in S147, and H-shaped structures with a prominent bar, similar to the one observed in the 3C 397 remnant. At small scales, the jets form clumps and filaments, resulting from instabilities and
vortices that the jets induce in the ejecta as they interact with the stellar material. We did not aim the simulation to reproduce any particular CCSN remnant, but rather to explore the resulting morphological features. Our finding of simulated features similar to observed ones supports the role of jets in exploding CCSNe and, in turn, supports the claim that the JJEM is the primary explosion mechanism of CCSNe.
Read the full abstract ▾
High Energy Astrophysical Phenomena
Probing the details of relativistic electrons with multifrequency observations of M87 black hole
J.G.J. Keuper and M. Moscibrodzka
Beginning in March 2026, the Event Horizon
Telescope (EHT) conducted a two-month observing campaign aimed at obtaining the first time-resolved sequence of images of the black hole M87* at the center of the Virgo A
galaxy. The primary scientific objectives of this campaign are to constrain the black hole
spin and to investigate the temporal variability of the
magnetic field and
plasma properties within the horizon-scale jet-launching region. In this work, we present theoretical predictions for the spectral index maps expected from these observations. Our predictions are based on Magnetically Arrested Disk simulations performed with the EBHLIGHT code and post-processed using the IPOLE general relativistic ray-tracing code. We investigate the temporal
evolution of the spectral index for a range of electron distribution models and five different black hole
spin values. The analysis includes both frequency bands currently present within the EHT and neighboring frequencies proposed for future extensions of the EHT array. In addition to extending previous studies to a broader range of observing frequencies, our work systematically investigates the time variability of the predicted spectral index maps. In purely thermal electron models, the temporal variability of the spectral index maps closely traces variations in the
magnetic field strength and electron temperature in the immediate vicinity of the event horizon. By contrast, models incorporating a non-thermal electron population exhibit substantially weaker spectral index variability, owing to the contribution of a power-law component with a fixed spectral slope. Our numerical results are consistent with theoretical expectations. Finally, a comparison with the recently measured integrated spectral index of the M87* enables us to place preliminary constraints on the model parameters.
Read the full abstract ▾
Instrumentation and Methods for Astrophysics
An RFSoC-based Backend and Timing System for the Balloon-borne Very Long Baseline Interferometry Experiment
Mayukh Bagchi, Felix M. Thiel, Laura M. Fissel et al. (+13 more)
We present the design and performance characterization of the digital backend and precision-timing system for the Balloon-borne Very Long Baseline Interferometry Experiment (BVEX), a pathfinder for high-frequency stratospheric VLBI at 22 GHz. The backend uses one of the four 14-bit analog-to-digital converter inputs on an AMD-Xilinx RFSoC 4x2. Although the converters support sampling rates up to 5 GSPS, the flight configuration digitizes the 2-4 GHz intermediate frequency at 4.096 GSPS. CASPER firmware provides both a high-resolution spectrometer for pointing and receiver verification, and a VLBI acquisition chain with two-bit requantization that records at a rate of about 8.2 Gbps. The timestamped data packets are sent over 100 Gigabit Ethernet (GbE) to a 16 TB NVMe array in a storage computer that draws approximately 70-80 W. The timing chain uses a Rakon oven-controlled
crystal oscillator as a timing reference while a time-interval counter measures its drift relative to a GPS reference with approximately 60 ps resolution. This is the first deployment of an RFSoC-based VLBI backend and precision-timing system on a stratospheric balloon. Ground tests validated the backend, spectrometer, and timing chain. The August 2025 CSA STRATOS flight ended before reaching the target float altitude because of a balloon failure, and as a result no science observations were obtained. For the planned 2027 reflight, we are developing a conduction-cooled data storage computer with 24 TB of NVMe capacity and a direct data path from the 100 GbE interface to the NVMe array.
Read the full abstract ▾
All authors Mayukh Bagchi, Felix M. Thiel, Laura M. Fissel, Maggie Oxford, Lindy Blackburn, Rafael Costa, Vincent L. Fish, Daryl Haggard, Michael D. Johnson, Dominic W. Pesce, Ganesh Rajagopalan, Javier L. Romualdez, Aarchi Shah, Adrian K. Sinclair, Stephanie St-Jean, Terry Yang
Instrumentation and Methods for Astrophysics
Towards First Light for MICADO: Validation of the PSF-R service with real data
Matteo Simioni, Luca Cortese, Roland Wagner et al. (+12 more)
MICADO, one of the ELT first-light instruments, will rely on point-spread-function reconstruction (PSF-R) to meet scientific requirements, especially for SCAO observations of targets that lack bright reference
stars nearby. PSF-R will be performed in post-processing using only AO telemetry, recorded simultaneously with the science data. For SCAO observations, both on- and off-axis PSFs will be delivered. We present the current status and results from an ESO TTR campaign begun in 2023, targeting a sparse three-
star asterism under varying conditions with the ERIS instrument at VLT. Reconstructed PSFs reach ~10% accuracy in Strehl ratio and FWHM at separations up to half the size of the isoplanatic patch. The current results suggest the telemetry-driven approach can reproduce not only the core PSF structure but also the extended wings, which are essential for reliable photometry and morphological analysis of bright extended sources. The obtained results also corroborate the key role of wind as a limiting factor of the method, reducing the amount of recovered information on specific directions.
Read the full abstract ▾
All authors Matteo Simioni, Luca Cortese, Roland Wagner, Carmelo Arcidiacono, Andrea Grazian, Marco Gullieuszik, Elena Masciadri, Elisa Portaluri, Benedetta Vulcani, Anita Zanella, Richard Davies, Johanna Hartke, Roberto Piazzesi, Stefan Raffetseder, Piero Vaccari
Instrumentation and Methods for Astrophysics
The MICADO first light imager for the ELT: the PSF Reconstruction Software
Andrea Grazian, Fernando Pedichini, Matteo Simioni et al. (+14 more)
The MICADO instrument for the ESO ELT will provide Adaptive Optics (AO) diffraction-limited NIR imaging and spectroscopy. A critical component of MICADO is the Point Spread Function Reconstruction (PSF-R) Software, which is designed to perform a blind reconstruction of the PSF for all observations using AO telemetry data only, both with the Single Conjugate (SCAO) and Multi-Conjugate Adaptive Optics (MCAO) modes of MICADO. The SCAO PSF-R Pipeline is currently being completed, and validation with ERIS at VLT and SOUL+LUCI at LBT has demonstrated high accuracy, of percent-level on-axis and 5-20% off-axis. Initial scientific simulations confirm that the PSF-R software meets the necessary precision for high-quality analysis, securing its role for MICADO's first light and future ELT operations.
Read the full abstract ▾
All authors Andrea Grazian, Fernando Pedichini, Matteo Simioni, Jani Achren, Carmelo Arcidiacono, Luca Cortese, Ric Davies, Marco Gullieuszik, Johanna Hartke, Hanindyo Kuncarayakti, Roberto Piazzesi, Elisa Portaluri, Stefan Raffetseder, Piero Vaccari, Benedetta Vulcani, Roland Wagner, Anita Zanella
Astrophysics of Galaxies
Testing Chemical Tagging with LAMOST: Intrinsic Abundance Dispersion of Subgiant Stars in the Galactic Disk
Wu Yaqian, Xiang Maosheng, Zhao Gang et al. (+4 more)
The scatter in elemental abundances among
stars of similar age and
metallicity reflects chemical inhomogeneity in their birth environments, making abundance scatter a key observable for chemical-tagging studies of Galactic formation and
evolution. Using a large sample of subgiant
stars with precise ages and elemental abundances derived from LAMOST low-resolution spectra, we investigate the intrinsic chemical abundance scatter of the low-$\alpha$ thin disk near the solar neighborhood ($7 < R < 10$ kpc). We model the abundance ratio [X/Fe], for each of the 19 elements of concern, as a function of age, [Fe/H], and [Mg/Fe], and deduce the intrinsic dispersions with a forward modelling technique. Our results confirm previous findings that the intrinsic scatters are small, typically $\lesssim0.05$~dex, for light elements (C, Al), $\alpha$-elements (O, Mg, Si, Ca, Ti), and iron-peak elements (Mn, Ni). A dedicated analysis of M67 yields similarly small scatter values for these elements, implying limited discriminatory power from light-element abundances alone. In contrast,
neutron-capture elements exhibit substantially larger scatters, typically $\gtrsim$0.1 dex, which are significantly larger than those of M67 member
stars ($\sim$0.07~dex). In particular, our analysis suggests that the abundance variations of individual
neutron-capture elements cannot be explained by a single tracer such as [Ba/Fe]. These findings clarify the utility of
neutron-capture elements for chemical tagging and highlight the potential of low-resolution spectroscopy in such studies.
Read the full abstract ▾
All authors Wu Yaqian, Xiang Maosheng, Zhao Gang, Jiang Ruizheng, Li Zhuohan, Bi Shaolan, Zhang Meng
Solar and Stellar Astrophysics
Evidence for CME–CME Interaction in a Magnetic-Cloud-Like Ejecta: Insights from Multipoint Observations and Polytropic Analysis
Jyoti Sheoran, Vaibhav Pant, Eva Weiler et al. (+5 more)
Using in-situ observations from Solar Orbiter, STEREO-A, and Wind, we investigate the heliospheric
evolution of an interplanetary coronal mass ejection (ICME). The
magnetic ejecta (ME) shows a
magnetic-cloud-like (MCL) configuration: a front region in which the
magnetic field rotates and its magnitude declines, followed by a weakly rotating "back region" of nearly constant field magnitude. Near-Sun EUV and white-light observations reveal two fast CMEs launched in rapid succession and interacting at low coronal heights, providing direct evidence that an MCL ejecta can arise from interaction between two closely spaced CMEs sampled near their apex. Using near-radially aligned Solar Orbiter and STEREO-A observations, we find that the sheath expands more rapidly than the ME, consistent with the "snow-plow" effect, while the ME properties broadly follow trends reported in previous ICME studies. Comparison of STEREO-A and Wind observations, separated by only 9.2 degrees in longitude, reveals measurable mesoscale variability within both the sheath and the ME. We identify dual polytropic behavior within both substructures, consistent with the merging of two interacting CMEs to form the observed MCL ejecta. This dual behavior in the ME is most pronounced in the inner heliosphere and weakens with heliocentric distance, indicating thermodynamic homogenization during radial expansion, whereas the sheath maintains thermodynamic contrasts from the inner heliosphere to 1 au. Our findings suggest that polytropic diagnostics can help reveal thermodynamically distinct
plasma populations associated with interacting CMEs, providing additional evidence for CME-CME interaction in MCL ejecta where conventional in-situ signatures show no clear evidence of such interactions.
Read the full abstract ▾
All authors Jyoti Sheoran, Vaibhav Pant, Eva Weiler, Vivek Menon, Emma E. Davies, Christian Möstl, Dipankar Banerjee, M. Saleem Khan
Solar and Stellar Astrophysics
Evidence for plasmoid formation related to a hot UV burst in the solar atmosphere
Mats Ola Sand, Luc Rouppe van der Voort, Souvik Bose et al. (+4 more)
Magnetic reconnection in the solar atmosphere drives energetic phenomena such as Ellerman bombs, UV bursts, and surges. We used coordinated observations from the Swedish 1-m Solar
Telescope (SST), IRIS, SDO, and the Hinode/X-ray
Telescope (XRT) to analyze an active region with strong
magnetic flux emergence. This region displayed long duration UV burst activity, occurrence of multiple Ellerman bombs, and recurrent ejection of surges. Chromospheric imaging show sthe presence of a dome-like structure that overarched the region where
magnetic flux was emerging. The curved chromospheric fibrils were closely associated with bright and similarly curved extensions from a UV burst in the IRIS 1400 A channel. We observed an episode of formation of a bright sheet along the curved fibrils in H-beta that subsequently fragmented into plasmoid-like blobs with peak emission at a Doppler offset of +43 km/s. IRIS Si IV lines in the same region show complex and non-Gaussian line profiles that display asymmetric extensions to high Doppler offsets. Some profiles have clear components with Doppler offsets in excess of 150 km/s on both sides of the nominal line center. The optically thin SDO/AIA channels, including 94 A, show intermittent and repeated occurrences of the burst. Emission measure and filter ratio analysis indicate that the burst is multi-thermal and can attain temperatures beyond 1 MK. AIA and Hinode/XRT observations reveal a localized EUV and soft-X-ray counterpart of the burst/dome system, supporting the presence of intrinsically multithermal
plasma that reaches coronal, and likely multi-MK, temperatures.
Read the full abstract ▾
All authors Mats Ola Sand, Luc Rouppe van der Voort, Souvik Bose, Daniel Nobrega-Siverio, Jonas Thoen Faber, Reetika Joshi, Ignasi Josep Soler Poquet
High Energy Astrophysical Phenomena
Cosmological Evolution of Primordial Black Holes: UV/IR Decoupling and the KM3NeT 220 PeV Neutrino Anomaly
Debdatta Dey, Tausif Parvez and S. Shankaranarayanan
The recent observation of a 220 PeV
neutrino event (KM3-230213A) by the KM3NeT observatory presents a formidable challenge to standard astrophysical source models. We investigate the hypothesis that this ultra-high-energy signature originates from the terminal evaporation burst of a Primordial Black Hole (PBH). Since PBH
evolution spans
cosmic history, static
vacuum approximations fail to capture early-universe dynamics.
Embedding the PBH in a cosmological background via the McVittie spacetime, we demonstrate that early-universe cosmological
accretion and expansion-suppressed Hawking emission shift the required initial mass window for a terminal burst occurring today. We show that although the early universe environment dictates the black hole's overall lifespan, its final explosion today ($z \approx 0$) is governed by standard Schwarzschild thermodynamics. This mechanism naturally produces the intense 220 PeV local flux while suppressing early emissions, thereby satisfying diffuse isotropic background limits. Consequently, this dynamical framework alters the mapping between current ultra-high-energy
neutrino observables and the primordial
curvature perturbations that seeded them.
Read the full abstract ▾
Astrophysics of Galaxies
Generating the wide sequence of Diffuse Galaxies with de Broglie waves of Dark Matter
Jiashuo Zhang, Tom Broadhurst, Alvaro Pozo et al. (+9 more)
Extensive Euclid satellite imaging at low surface brightness has revealed that most nearby
galaxies are diffuse-looking spheroids, where the stellar radius increases for over three decades in luminosity. We argue this Diffuse
Galaxy sequence results from internal stellar
diffusion by Wave Dark Matter ($\psi$DM), as wave energy is transferred to
star orbits over time. In particular, the
soliton random motion scatters central
stars onto radial orbits that become enhanced with each passage through the centre, slowly “puffing up" the stellar profile. Heating is greater within massive
galaxies as $\psi$DM fluctuations are stronger and more frequent, reproducing both the Diffuse
Galaxy sequence and the rising velocity dispersion along the sequence, from Ultra-Faint to Dwarf Spheroidal and Ultra Diffuse
galaxies, favouring a light
boson, $m_\psi=2.88^{+0.14}_{-0.13}\times10^{-22}$eV. Winding back this
diffusion, we predict the stellar content of Diffuse
Galaxies, including globular clusters, formed near the centre, as anticipated by $\psi$DM simulations, where gas cools efficiently within the dense
soliton. This predicted $\psi$DM
evolution from compact beginnings towards diffuse spheroidal
galaxies today can now be fully charted from JWST to Euclid.
Read the full abstract ▾
All authors Jiashuo Zhang, Tom Broadhurst, Alvaro Pozo, Tzihong Chiueh, Justin Schive, Bo-Ren You, Jeremy Lim, Francine Marleau, Tomomi Sunayama, Keiichi Umetsu, Mariam Bouhmadi-Lopez, Masamune Oguri
Astrophysics of Galaxies
Resonantly Scattered CIV Emission in Local Star-forming Galaxies: Radiative Transfer Constraints on High-ionization Gas in Reionization Analogs
Zhihui Li, Danielle A. Berg, Simon Gazagnes et al. (+4 more)
Rest-frame ultraviolet emission lines are diagnostics of hard ionizing spectra and highly ionized gas in
galaxies resembling the sources of
cosmic reionization. Nebular CIV emission traces both intrinsic line production and resonant scattering through its velocity-resolved profile. Previous studies have treated CIV empirically, using integrated fluxes, equivalent widths, and line ratios rather than modeling the radiative transfer (RT) shaping the emergent profiles. We present the first systematic RT modeling of resonantly scattered CIV emission profiles in 18 local
star-forming
galaxies observed with HST/COS. Using the clumpy RT framework PEACOCK, idealized experiments show that profile morphology is governed by column density, gas kinematics, intrinsic equivalent width, and aperture-dependent recovery of scattered emission. We fit continuum-normalized spectra corrected for stellar contributions with a neural-network-accelerated
Bayesian pipeline, reproducing P-Cygni-like, double-peaked, double-peaked with two absorption troughs, and blue-bump plus red-peak morphologies. Emission infilling connects these profile classes and complicates kinematic inferences, while aperture losses decouple observed net equivalent widths from intrinsic line production. Combining RT-inferred intrinsic equivalent widths with rest-UV diagnostics, we find that most
galaxies are consistent with stellar photoionization, although some may require harder spectra or more extreme ionization conditions. Comparison with CLASSY reveals stronger associations of stellar mass and
star formation rate with gas kinematics than with CIV column density. Our results establish CIV as both a tracer of hard ionizing radiation and a resonant-line probe of gas structure and kinematics, with velocity-resolved profiles providing information beyond integrated line strengths in local reionization analogs.
Read the full abstract ▾
All authors Zhihui Li, Danielle A. Berg, Simon Gazagnes, Timothy Heckman, Max Gronke, Dawn K. Erb, John Chisholm