Cosmology and Nongalactic Astrophysics
Constraining quantum-gravity predictions for evolving dark energy
M. Tsedrik, B. Bose, L. Marchetti et al. (+1 more)
We confront a class of dark-energy equations of state emerging from group field theory (GFT)
quantum gravity with DESI Data Release 2 baryon acoustic oscillations and Pantheon+ type-Ia
supernovae. We introduce sampling parametrisations that replace microscopic initial-condition parameters by combinations more directly measured by background probes. The GFT solutions separate into logarithmic, power-law and oscillatory branches, determined by the microscopic interaction parameter $m$. The logarithmic branch is constrained to lie extremely close to a cosmological constant, while the power-law branch permits a small phantom deviation. Without perturbative-theory priors, oscillatory solutions can reproduce the mild preference of the distance data for a dip in $w(z)$ near $z\simeq0.5$–$1$. Profile-likelihood constraints favour $m\sim-2$ and $m\sim-5$ from BAO and
supernovae, shifting towards $m\sim-3.5$ when CMB information is included. Conservative perturbative priors strongly suppress these deviations from $\Lambda$CDM. The
quantum-
gravity scale $z_q$, related to the average number of
quantum gravity atoms, remains unconstrained, although its role in the time
evolution makes higher-
redshift observations a promising route to probing it. We further find that strong projection effects highlight the importance of performing likelihood profiling alongside our marginal posterior constraints. Our results provide a first direct test of GFT-motivated dynamical dark energy and demonstrate the potential for cosmological observations to inform
quantum-
gravity model building.
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All authors M. Tsedrik, B. Bose, L. Marchetti, E. Ferreira
High Energy Astrophysical Phenomena
A Standard Ultraviolet Continuum Can Hide Supercritical Accretion in GN-z11
Samik Mitra and Ramananda Santra
The ultraviolet continuum from a high-
redshift accreting black hole is routinely used to infer its mass. GN-z11 offers a sharp test of whether that inference is secure. A thin-disk fit to its continuum gives an Eddington mass of $M_{\rm E}=1.12\times10^{7}\,\Msun$, an order of magnitude above the $\log(\Mbh/\Msun)=6.2\pm0.3$ inferred from broad N~iv. We show that this apparent tension is not imposed by the ultraviolet slope alone. We derive a closed-form criterion comparing the radius where observed
photons are produced with the radius where a supercritical flow departs from efficient solution. For GN-z11, the criterion places the supercritical transition inside the ultraviolet-emitting region. Composite disks retaining the outer solution confirm this numerically, requiring $\Mdot_{\rm out}=3.1$–$4.4\,\Msun\,\mathrm{yr^{-1}}$ and placing $\Rsph=(1.2$–$1.8)\times10^{3}\,\rg$ inside $\Ruv=(2.6$–$2.9)\times10^{3}\,\rg$. Replacing the inner $\sim10^{3}\rg$ by a supercritical flow shifts the fitted slope by only $\Delta\betaUV=+0.08$ to $+0.11$, comparable to uncertainties from standard spectral modelling. Reversing the radial ordering requires the effective transition to move outward by a factor $1.7$–$2.1$. Within our composite models, the measured slope constrains black-hole mass only to around $10^{6}\,\Msun$, an order of magnitude below the continuum Eddington mass. Continuum Eddington masses should therefore be treated as model-dependent bounds that assume global thin-disk efficiency. The same hierarchy appears in three additional JWST sources under the disk-dominated interpretation, where separation masses are only $4$–$6$% of continuum Eddington masses. This distinction can substantially weaken the seed-mass and early-growth demands inferred from ultraviolet continua at
cosmic dawn for the first massive black holes.
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High Energy Astrophysical Phenomena
Can Isotropic Thermal Conduction Heat One of the Hottest Cool Cores?
Samik Mitra, Ramananda Santra and Norbert Werner
Thermal conduction can act as a heating mechanism for cool-core clusters, yet the same transport must erode any temperature discontinuity it crosses. Ophiuchus permits both effects to be tested in the same atmosphere. Its temperature rises from about $1$ keV in the innermost core to $9$ keV at $r\sim30$ kpc, making conductive heating especially favorable, while two sharply resolved cold fronts independently constrain the same transport. \textcolor{black}{We construct a steady radial energy balance from deprojected Chandra density and temperature profiles, with XRISM-based limits on turbulent heating and a subsonic inflow contribution.} Closing the balance with conduction requires only sub-Spitzer coefficients — \Ftwentyfive\ at 25 kpc and \Finner\ and \Fouter\ at the inner and outer cold fronts — so conduction can energetically supply the missing heat. Yet the same coefficients, applied normal to the cold-front surfaces, would broaden the fronts to their observed width limits within \Tinner\ and \Touter\ Myr, short compared to the characteristic sloshing timescales that generate and sustain such interfaces. For a representative 200 Myr residence time, the radial conductivity demanded by the energy balance exceeds the cross-front conductivity permitted by front survival by roughly a factor of three, with the required anisotropy exceeding unity in 99.9% and 98.8% of accepted models. The result leaves two broad regimes. Thermal conduction is either subdominant in Ophiuchus or contributes substantially but is strongly anisotropic, with heat transport suppressed across the cold fronts relative to the radial direction. Together they disfavor locally isotropic conduction as a dominant heating mechanism in cool cores generally.
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High Energy Astrophysical Phenomena
Validating Inverse Fundamental-Plane IMBH Mass Estimates in the SKA/ngVLA Era
Shahram Abbassi, Samik Mitra and Ramananda Santra
The
radio/X-ray/black-hole-mass Fundamental Plane (FP) is widely used to estimate masses of accreting intermediate-mass black hole (IMBH) candidates. Its inverse use is justified only when
radio luminosity traces a compact jet core and X-rays arise from the same sub-Eddington hard-state
accretion flow. We formulate an
accretion-state validity criterion for inverse-FP masses using verified BH X-ray binary
radio/X-ray tracks as the empirical reference. Using 424 detections from 21 BHXBs and candidates, we find that both standard and curved tracks are present and the luminosity at which
radio/X-ray behavior changes is source dependent. A low X-ray Eddington ratio is therefore not, by itself, sufficient to establish inverse-FP validity. Within a scale-invariant jet/hot-flow framework, track steepening reduces the effective mass leverage of the inversion, while at much lower
accretion rates uncertainties in the dominant emission mechanism and compact-core production can invalidate the underlying FP assumptions altogether. We apply the criterion to representative IMBH-relevant systems without fitting a new plane. NGC 4395 is low-Eddington but compact-
radio deficient: its VLA-scale and VLBI jet-base luminosities imply formal inverse-FP mass underestimates of about 1.0 and more than 2.8 dex if the deficit is misread as a mass signal. Globular-cluster X-ray populations in NGC 1399 and NGC 4472 are source-identity limited: 71% and 67% lie below $L_{\rm Edd}(10\,M_\odot)$, and the high-luminosity tail alone does not identify an IMBH accretor. The
radio non-detection of the $\omega$ Centauri IMBH candidate constrains gas supply,
accretion efficiency, and compact-core production rather than excluding the black hole. The resulting test defines which SKA/ngVLA-era
radio cores can be converted into FP masses, and which instead constrain gas supply, source identity, or compact-core production.
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Instrumentation and Methods for Astrophysics
MUSHY: Multimodal Flow-Based Amortized Bayesian Inference for Spectroscopic Data Fusion
Jeff Shen
We are in an era of unprecedented spectroscopic data availability, with surveys such as APOGEE, GALAH, and DESI observing millions of
stars. However, data are heterogeneous and to date, efforts to exploit synergies between surveys have been limited. In particular, there is a lack of principled methods that combine spectroscopic data from different surveys to improve inference of physical parameters. In this work we present a new method, MUSHY, for spectroscopic data fusion. MUSHY is an amortized
Bayesian inference method, using a rectified flow model with
multimodal inputs to learn a posterior distribution over physical parameters. Using synthetic spectra generated via ATLAS12/SYNTHE, including realistic instrumental effects and noise, we demonstrate that MUSHY can precisely infer physical parameters with well-calibrated posteriors from any combination of surveys, with
multimodal inputs providing stronger constraints on the posterior than single-survey data alone. This work paves the way for principled combination of spectroscopic data from heterogeneous sources.
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Cosmology and Nongalactic Astrophysics
NERV: Neural-network Enhanced Reconstruction of the UniVerse with Application to Baryon Acoustic Oscillations in the BOSS DR12 Galaxy Sample
Shi-Hui Zang, Hong-Ming Zhu, Tian-Xiang Mao et al. (+1 more)
We present the first application of neural-network-based baryon acoustic oscillation (BAO) reconstruction to real
galaxy survey data, restoring the acoustic signature damped by nonlinear structure growth. {NERV} (Neural-network Enhanced Reconstruction of the UniVerse) augments standard reconstruction with a convolutional neural network trained on cubic $N$-body simulations, and explicitly accounts for realistic observational effects including the curved-sky geometry, the
redshift-dependent selection function, and finite survey boundaries, by tessellating the survey volume into local patches. We validate the method on the MultiDark-Patchy mock catalogs, recovering unbiased BAO dilation parameters. Applied to the BOSS DR12
galaxy sample, NERV improves the precision of the BAO distance measurements significantly. These results establish neural reconstruction as a practical component of BAO analyses for ongoing surveys such as DESI, with the potential to substantially tighten constraints on the
cosmic expansion history and the nature of dark energy.
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All authors Shi-Hui Zang, Hong-Ming Zhu, Tian-Xiang Mao, Ue-Li Pen
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Distinguishing cosmology, astrophysics and systematics: the Bayesian search for a primordial gravitational-wave background in next-generation observatories
Teagan A. Clarke, Sylvia Biscoveanu and Carl-Johan Haster
Next-generation gravitational-wave observatories like
Cosmic Explorer will provide an unprecedented opportunity to probe the cosmological
stochastic gravitational-wave background, providing insight into the early Universe that is inaccessible with other means. We investigate the prospects for measuring a Gaussian cosmological gravitational-wave background in
Cosmic Explorer in the presence of a distinguishable, non-Gaussian foreground of binary black hole mergers, using a
Bayesian search that simultaneously fits binary black hole and background parameters. We successfully recover a Gaussian cosmological background with a signal-to-noise ratio of 5 in one day of simulated data in
Cosmic Explorer without contamination from unresolved signals or data exclusion. However, when introducing waveform systematic errors to our analysis, our inference on the
stochastic background parameters becomes biased and can falsely infer the presence of a background when there is none. The bias is driven by signal mismatches at low frequencies (<20 Hz), especially when the recovery waveform is missing physical effects included in the injected signals. While we propose a metric for diagnosing if measurements will be strongly biased by waveform systematics, our results suggest improvements in waveform modeling or other mitigation techniques will be required to accurately recover a primordial
stochastic gravitational-wave background in next-generation detectors.
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Instrumentation and Methods for Astrophysics
Disentangling 3D Magnetic Field Geometry from Turbulence: A Polarization-Based Classification Method
Sophia Kressy and Fabian Heitsch
We develop a decision tree classifier that recovers 3D
magnetic field geometry from synthetic polarization and position angle maps of a magnetized, turbulent field. We test the classifier for a series of geometries: Uniform, Wavy, Helical, and Hourglass. The classifier is calibrated across a range of Alfvénic Mach numbers and injected Stokes Q,U noise levels for each geometry. Our models show the median and skewness of the polarization fraction, as well as the position angle circular variance, vary systematically with both geometry and the Alfvénic Mach number. We find that the 3D geometry can be isolated by using a variety of polarization and position angle metrics to break degeneracies. The classifier recovers most geometries well for sub-Alfvénic cases (Alfvénic Mach Number < 1). For Alfvénic Mach Number > 1, polarization and position angle statistics converge across all geometries and the classifier fails to recover the
magnetic field structure.
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Astrophysics of Galaxies
Common Excitation Patterns of Star Formation, Active Galactic Nuclei, and Shocks in Seyfert Galaxies
Peixin Zhu, Lisa J. Kewley, Dominika Ł. Król et al. (+6 more)
The growth of
galaxies and their central supermassive black holes is closely connected, yet the net effect of active galactic
nuclei (AGN) feedback on host-
galaxy star formation remains uncertain. AGN may enhance, suppress, or have little measurable impact on
star formation, but distinguishing among these outcomes requires separating
star-formation and AGN photoionization from shock excitation, which is expected in AGN-driven outflows but has been difficult to isolate. Here we apply a recently developed theoretical three-dimensional diagnostic diagram, designed to separate
star formation, AGN, and shock excitation, to VLT/MUSE IFU observations of nine nearby (z < 0.026) Type 2 Seyfert
galaxies. We find a common excitation pattern across the sample:
star-forming rings or arcs at projected radii of r~0.8-6 kpc, AGN-photoionized bicones extending to kpc scales, central fast-shock-dominated regions that often extend perpendicular to the AGN bicone, and pure-shock- dominated regions surrounding the central fast shocks and appearing locally within the
star-forming rings. Deep Chandra X-ray morphology independently supports this decomposition. The circumnuclear
star-forming rings are consistent with bar-driven resonances, although positive AGN feedback may also contribute. The central fast shocks are broadly consistent with AGN jet-ISM interactions, while AGN wind-ISM interactions may also play an important role in
galaxies with low-power jets. These results establish central shocks as a common feature of Seyfert
galaxies and demonstrate the importance of accounting for shock excitation in AGN feedback studies.
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All authors Peixin Zhu, Lisa J. Kewley, Dominika Ł. Król, Giuseppina Fabbiano, Lars Hernquist, Ralph S. Sutherland, Anna Trindade Falcão, Martin Elvis, Riccardo Middei
Solar and Stellar Astrophysics
The JWST Proto-PAH Project: Detection of the methyl radical CH$_{3}$ in the highly evolved C-rich object SMP LMC 011
Jialu Li, D. A. García-Hernández, A. Manchado et al. (+17 more)
We report the first detection of the neutral methyl radical CH$_3$ in a highly evolved C-rich object, SMP LMC 011, using JWST MIRI/MRS. CH$_3$ is well fitted by an excitation temperature of $T_{\rm ex} \simeq$~190\,K and a column density of $N_{\rm tot}(\mathrm{CH_3}) \simeq 5.6\times10^{17}$ cm$^{-2}$. We also report the non-detection of ethane (C$_2$H$_6$), consistent with CH$_3$ reacting preferentially with unsaturated radicals rather than self-recombination, which may be inefficient in SMP LMC 011. Combined with the exceptionally large benzene column density of SMP LMC 011, this supports a methyl-addition route from benzene towards alkyl-substituted aromatics. We propose that the high CH$_3$ abundance is driven by the erosion of hydrogenated amorphous carbon (HAC) dust grains in the dense warm
torus by UV
photons from the central
star and/or by shocks, which release CH$_3$ directly into the gas phase. These results establish CH$_3$ as a key reactive intermediate in the formation of complex hydrocarbons in C-rich circumstellar environments. Chemical models that incorporate methyl-addition reactions are needed for a better understanding of PAH formation pathways in evolved
stars. The potential detection of alkyl-substituted aromatics such as toluene (C$_7$H$_8$) and ethylbenzene (C$_8$H$_{10}$) in C-rich evolved
stars would provide direct confirmation of CH$_3$-driven aromatic growth in circumstellar environments.
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All authors Jialu Li, D. A. García-Hernández, A. Manchado, Debayan Das, J. Cami, Els Peeters, G. C. Sloan, B. Aringer, J. Bernard-Salas, C. Bhatt, Nicholas Clark, Harriet L. Dinerstein, M. A. Gómez-Muñoz, Kathleen E. Kraemer, M. Matsuura, R. Sahai, N. C. Sterling, Kevin Volk, G. M. Wahlgren, A. A. Zijlstra
High Energy Astrophysical Phenomena
Ce II-IV emission in kilonovae with R-matrix collision strengths and distorted wave recombination rates
Leo Patrick Mulholland, Niamh Ferguson, Luke J. Shingles et al. (+3 more)
We provide transition probabilities and Maxwellian-averaged collision-strengths for the electron-impact excitation of Ce ii - iv. These ions are potentially abundant in kilonovae (KNe) and feature both forbidden and allowed transitions in the infrared. These atomic data are obtained using the grasp$^0$ atomic structure code, interfaced with the non-perturbative darc R-
matrix close-coupling codes. We additionally use autostructure to produce dielectronic and radiative recombination rate coefficients for Ce ii - vi. Using this data, we calculate an approximate ionization balance including non-thermal ionization rates with deposition rates from realistic models. We find Ce ii - iv to be of roughly equal abundance, subject to ejecta conditions. We find that generally we need $\gtrsim$ 10$^{-3}$ M$_{\odot}$ of Ce in total to produce emission of comparable luminosity to the features in the spectrum of AT2023vfi. In particular, it is found that [Ce iv] 4.5 $\mu$m requires both strong ionization and weak recombination, as well as a production of Ce considerably stronger than that of the solar abundance in order to have luminosity comparable to the apparent emission in this wavelength vicinity in \grb. %which is seemingly incompatible with the current understanding of the bulk composition of KNe. With such strict requirements on individual element masses, the detection of individual lanthanides on a line-by-line basis in the nebular phase seems unlikely - but lanthanides may remain important for cooling and early time analyses.
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All authors Leo Patrick Mulholland, Niamh Ferguson, Luke J. Shingles, Catherine A. Ramsbottom, Connor P. Ballance, Stuart A. Sim
High Energy Astrophysical Phenomena
Impact of uncertainties on the cosmic optical and infrared backgrounds on the propagation of astroparticles
Lucas Gréaux, Antonio Condorelli, Leonel Morejon et al. (+2 more)
When propagating through the universe, gamma rays at very-high energy (VHE, E > 100 GeV) and ultra-high energy
cosmic rays (UHECRs, E > 1 EeV) can interact with the optical, infrared and microwave
photon fields that permeate the universe. These interactions result in a characteristic absorption imprint in the spectra of extragalactic gamma-ray sources at VHE, and in a change in the mass-composition of UHECRs. The study of both VHE gamma rays and UHECRs therefore requires precise knowledge of the intensity of the
cosmic photon fields. In this work, we explore the impact of the current uncertainties on the optical and infrared
photon fields on the propagation of astroparticles. We restrict the range of available models to those best matching the recent measurements, and compare the different reconstructions resulting from these models. We find that the knowledge on the
cosmic background light is no longer the dominant source of uncertainties in understanding the phenomenology of astroparticle sources in the low
redshift universe (z < 0.1), enabling robust spectral and composition inference with the next generation of both gamma-ray and UHECR measurements.
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All authors Lucas Gréaux, Antonio Condorelli, Leonel Morejon, Karl-Heinz Kampert, Jonathan Biteau
Astrophysics of Galaxies
Rubin Observatory Reveals a Dust-Shrouded Halo Globular Cluster in Ophiuchus
Aashay Pai, William Cerny, Andrew B. Pace et al. (+9 more)
We present the discovery of the Milky Way satellite Rubin-GC1 (Rubin J1628-1735) using data from the NSF-DOE Vera C. Rubin Observatory's Early Data Preview 2. The system was discovered in the direction of the Galactic bulge with $(l, b) \sim (359^{\circ}, 21^{\circ})$ in a region of high stellar density and a foreground reddening of $E(B-V) \approx 0.7$. We simultaneously fit the morphology and isochrone parameters of Rubin-GC1, determining that it is a faint ($M_V = -2.4^{+0.5}_{-0.7}$) and compact ($r_{1/2} = 5^{+1}_{-1}$ pc) Milky Way satellite at a distance of $D_\odot = 31^{+3}_{-3}$ kpc; its stellar population is intermediate-age ($\tau=9.2^{+1.2}_{-0.7}$ Gyr) and moderately metal-rich ($\mathrm{[Fe/H]_{iso}}=-0.73^{+0.04}_{-0.04}$). Together, these properties suggest Rubin-GC1 is most likely a
star cluster in the faint tail of the luminosity function of globular clusters surrounding the Milky Way. We identify a distinct proper motion signature from Rubin-GC1 in Gaia DR3, and from a comparison of the system's 5D phase space information to $N$-body models of the Sagittarius dwarf spheroidal
galaxy's tidal stream, we determine that Rubin-GC1 is likely an accreted cluster associated with the Sagittarius leading arm. The discovery of Rubin-GC1 highlights the potential of Rubin to uncover faint, resolved satellites in dust-shrouded regions of the Milky Way, including remnants of the
accretion events that have shaped the
Galaxy's hierarchical assembly.
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All authors Aashay Pai, William Cerny, Andrew B. Pace, Alex Drlica-Wagner, Peter S. Ferguson, Marla Geha, Chin Yi Tan, Sasha N. Campana, Burçin Mutlu-Pakdil, Alexander H. Riley, Nora Shipp, Guy S. Stringfellow
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Neutron Skin Effects on Particle Emission in Heavy-Ion Collisions: A Topic Review with Astrophysical and Nuclear Structure Connections
Bao-Jun Cai, De-Qing Fang and Yu-Gang Ma
The
neutron skin, defined by the difference between
neutron and
proton root-mean-square radii, is a characteristic manifestation of isospin asymmetry and an important probe of the isovector nuclear interaction. This focused review examines how
neutron skins influence particle emission and collective dynamics in heavy-ion collisions, from the Fermi-energy regime to ultra-relativistic energies. By modifying the initial
neutron and
proton density profiles, the
neutron skin affects the isospin composition and geometry of the participant region, pre-
equilibrium emission, particle production, fragment formation, and collective flow. We review
neutron-to-
proton and $\rm{t}/^3\rm{He}$ yield ratios, light clusters, pion ratios, bremsstrahlung
photons, isoscaling and fragment momentum distributions, and
neutron-
proton differential flow and momentum observables, emphasizing their interplay with the
symmetry energy and transport dynamics. At high energies,
neutron skins also modify the initial geometry, eccentricities, multiplicities, and anisotropic flows in isobar and heavy-
nucleus collisions. We discuss the challenge of disentangling these effects from deformation, surface diffuseness, shell structure, clustering, and model dependence. Broader connections to parity-violating electron scattering, dipole responses, coherent elastic
neutrino-
nucleus scattering, SRC-induced
proton skins in momentum space, and
neutron-
star observables are also explored. Finally, we highlight opportunities from radioactive beams, improved collision experiments, microscopic many-body and transport calculations, and
Bayesian inference. Combining multiple reaction systems and observables with complementary nuclear-structure and astrophysical information will be essential for quantitatively constraining
neutron skins and the density dependence of the
symmetry energy.
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Cosmology and Nongalactic Astrophysics
Cosmological Signatures of Curvature-Coupled Dark Energy
Abdolali Banihashemi, Farbod Hassani, Alessandro Casalino et al. (+2 more)
We study a
curvature-coupled dark energy model that can modify cosmological
evolution both before recombination and during the late-time accelerated era. The model belongs to the class of scalar-tensor theories, in which a quintessence field is non-minimally coupled to the Ricci scalar. We specify the model through a shifted quartic coupling, $f(\varphi)=\alpha(\varphi^2-\varphi_{\rm today}^2)^2$, and an inverse power-law potential, $V(\varphi)=\Lambda\varphi^{-\sigma}$, where $\varphi_{\rm today}$ is a constant fixed by requiring the effective Planck mass to recover its present-day normalization. We implement the model in a modified version of $\mathtt{hi\_class}$ and compute its background and linear cosmological predictions. This specific form of non-minimal coupling allows an effective crossing of the phantom divide at late times while naturally suppressing deviations from standard
gravity today and satisfying local
gravity constraints. At the same time, the scalar field can modify the expansion history before recombination, shifting the acoustic scale in the direction required to alleviate the $H_0$ tension, while remaining dynamically relevant as dark energy at low
redshift. For the parameter choices studied here, we find tens-of-percent deviations from $\Lambda$CDM in the expansion history, matter clustering, and metric-potential spectra. The modified
evolution of the gravitational potentials leaves characteristic signatures in relativistic observables, with weak-
lensing power suppressed by $\mathcal{O}(20$-$40\%)$ at low multipoles and order-unity changes in the late Integrated Sachs-Wolfe signal. Together, these results reveal a broad, scale-dependent phenomenology that motivates both a full parameter-space analysis and an extension of the present linear treatment to a dedicated non-linear $N$-body implementation.
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All authors Abdolali Banihashemi, Farbod Hassani, Alessandro Casalino, David F. Mota, Emilio Bellini
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Analysis of GWTC-3 with multiple quasicircular models
N. Manning and R. O'Shaughnessy
The interpretation of gravitational wave sources depends on the specific choice of model used to interpret signals. Previous analyses of GWTC-3 event candidates using SEOBNRv4PHM, IMRPhenomXPHM, and NRSur7dq4 have sometimes arrived at notably different conclusions about event properties. Subtle analysis settings and code differences can also produce notable differences. We revisit 60 publicly available events from the first three observing runs, released across GWTC-1, GWTC-2, GWTC-2.1, and GWTC-3, using a consistent analysis framework and three waveform models: two state-of-the-art time-domain models with higher-order modes (SEOBNRv5PHM and IMRPhenomTPHM) and one older frequency-domain model without higher-order modes (IMRPhenomPv2). The two state-of-the-art models agree well overall, although about 20% of events have a visible difference in at least one one-dimensional marginal posterior. By contrast, the older model often arrives at qualitatively different conclusions for key events across the mass spectrum. We also identify a bug in published LVK GWTC-2.1 SEOBNRv4PHM results and in a later reprocessing of GW200105. At the adopted sampling rates, the model's Nyquist-frequency restriction excluded part of the allowed parameter space and artificially truncated the mass-ratio posterior away from equal mass for seven low-mass events. These results emphasize the need to use multiple state-of-the-art waveform models and carefully validated analysis settings to characterize uncertainty in gravitational-wave source properties.
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Solar and Stellar Astrophysics
Multi-chromatic observations of classical Cepheids using the CHARA Array interferometer: Surface brightness-colour relation, projection factor, and limb-darkening
M. C. Bailleul, N. Nardetto, D. Mourard et al. (+28 more)
The Baade-Wesselink (BW) method compares the linear and angular variations of Cepheids to derive their distance. This method is limited, however, by the projection factor, which relates the observed radial velocity to the true pulsation velocity of the
star. Using simultaneous observations from the CHARA Array interferometer in the K, H, and R bands with the MYSTIC, MIRC-X, and SPICA combiners, respectively, we aim to understand the physics of Cepheid atmospheres better. Applying a specific method to multi-chromatic simultaneous interferometric observations of Cepheids, we derived robust limb-darkened angular diameters that were then used to calibrate the SBCR and study the projection factor. We also developed a strategy to measure the limb-darkening of Cepheids in R, H, and K bands. These measurements were then used to constrain the geometrical component of the projection factor. From the limb-darkened angular diameter curves of three Cepheids, we decreased the scatter of the SBCR in $V-K$ colour to 0.0011 magnitude and to 0.0040 for the SBCR in $G_{BP}-G_{RP}$. These SBCRs are particularly robust because they are based on multi-chromatic diameters and are homogeneous, which previous calibrations for Cepheids were not. For the very first time, we derived the limb-darkening of Cepheids in R, H, and K bands. For $\delta$ Cep, we derived an R-based projection factor of $1.275 \pm 0.051$, and the geometrical part obtained from the measured limb-darkening coefficient in R band was estimated to $1.420 \pm 0.016$ (on average), as expected from stellar static and hydrodynamical atmosphere models. The limb-darkening coefficients obtained in H and K band are consistent with models. These results demonstrate that multi-chromatic interferometry can improve the accuracy of the BW method. It is therefore essential to continue the CHARA survey of Cepheids in the coming years.
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All authors M. C. Bailleul, N. Nardetto, D. Mourard, A. Mérand, P. Kervella, A. Gallenne, G. Bras, J. Monnier, K. Sivkova, B. Apostolova, L. Breuval, W. Kiviaho, W. Gieren, V. Hocdé, R. S. Rathour, G. Pietrzyński, P. Bério, F. Morand, D. Salabert, J. Jones, C. Lanthermann, N. Ebrahimkutty, J. Jonàk, H. Nowacki, R. V. Ibañez Bustos, M. Vrard, S. Kraus, N. Anugu, M. Gutierrez, N. Ibrahim, T. Gardner
High Energy Astrophysical Phenomena
Modeling Gamma-Ray Bursts Using CRISP
Leonel Morejon, Therese Paulsen and Karl-Heinz Kampert
Astrophysical
neutrinos are a clear identifier of photohadronic interactions in sources of Ultra-High-Energy
Cosmic Rays (UHECRs). As the Pierre Auger Observatory has shown that UHECRs exhibit a composition heavier than
protons at Earth, we expect that these heavy primaries undergo nuclear cascades due to photodisintegration in the dense source environments from which they originate. In this contribution, we will derive the
neutrino spectra including those originating from
nuclei undergoing photohadronic interactions. This will be explored in the context of modeling the emission region of a gamma-ray burst. Photohadronic interactions will be modeled using the new framework for
Cosmic Ray
Stochastic Interactions for Propagation (CRISP), which employs an analytic approach to compute the underlying probabilistic description of UHECR interactions.
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Earth and Planetary Astrophysics
Thermophysical characterization of the potentially hazardous near-Earth object 2024 YR4
T. G. Müller, E. M. MacLennan, A. Y. Burdanov et al. (+7 more)
The asteroid 2024 YR4 is a potentially hazardous Apollo-type near-Earth object. Its highly eccentric orbit produces close Earth-Moon encounters roughly every 4 years. A collection of light curves, including JWST-NIRCam data, allowed us to constrain the rotation period,
spin pole, and convex shape solutions for the object. We analyzed two sets of JWST-MIRI observations obtained in three filters on 26 March 2025. The extracted photometry reveals rotationally driven thermal flux variations. The combination of a
spin-shape model from light-curve inversion and the absolutely calibrated 3-band MIR light curves is well reproduced by a convex
spin-shape solution with a
spin pole at (l,b) = (232, -11), a sidereal period of 19.4633 min, and axis ratios of a/b ~1.28 and b/c ~1.45. The corresponding equivalent-volume diameter is 60.8 +1.8/-3.6 m (pV= 0.11 +0.05/-0.03, assuming HV = 24.14+/-0.25 mag). A high thermal inertia and low surface roughness are required to explain the observed MIRI data. The near-Earth asteroid thermal model has limited reliability for this object, requiring an extreme beaming parameter >3, whereas the fast-rotating model and a full thermophysical model provide consistent and reliable estimates of the size and albedo. The combination of high eccentricity and high thermal inertia implies seasonal skin depths of up to ~3 m and radiative timescales of weeks to months. Although seasonal heating is negligible for the March 2025 observations because of the near-equator-on viewing geometry, the seasonal Yarkovsky drift is expected to be dominant over the diurnal component and might become measurable during future encounters. Although JWST astrometry from February 2026 rules out any possible impact on the Earth or the Moon for at least 100 years, the
spin, shape, and radiometric constraints presented here provide an important
benchmark for future potentially hazardous objects.
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All authors T. G. Müller, E. M. MacLennan, A. Y. Burdanov, B. J. Holler, A. S. Rivkin, J. de Wit, P. Pravec, M. Micheli, K. Muinonen, D. Farnocchia
Cosmology and Nongalactic Astrophysics
Toward Precision Kinetic Sunyaev-Zel'dovich Cosmology—1. The Matter - Momentum Bispectrum at One-Loop Order
Ryan Raikman, James M. Sullivan and Mikhail M. Ivanov
The kinetic Sunyaev-Zeldovich (kSZ) effect is a sensitive probe of the free-electron momentum field, tapping into spatial correlations relevant for both large-scale cosmology and smaller-scale astrophysics. Precision kSZ measurements will provide a robust channel for constraining inflationary physics and equivalence principle violation, while simultaneously characterizing the small-scale gas distribution and associated baryonic feedback. However, robust kSZ measurement for cosmological applications is challenging, as the primary source of large-scale information is convolved with unknown small-scale dynamics in a degenerate combination. In this paper we address this challenge using the Effective Field Theory (EFT) framework that provides a principled way of treating the effects of small-scale dynamics on large scale-structure. Extracting the kSZ signal can be reformulated as a measurement of the one-loop
galaxy-
galaxy-electron momentum bispectrum. We compute here a pure dark matter version of this bispectrum in EFT and compare it to simulations. We derive the EFT counterterms that capture small-scale backreaction and find that two of them acquire a transverse direction. One transverse counterterm gets generated entirely by the vorticity of the velocity field. Our computation of the bispectrum dipole agrees with simulation data to 5% up to k_max = 0.23 h/Mpc, which is significantly larger than the reach of tree level theory, which breaks down beyond k_max = 0.07 h/Mpc (at
redshift z = 0.5). For the bispectrum computed with the projected momentum field, relevant to measuring the kSZ field, we find a similar k_max, and make the first detection of the transverse counterterms from simulations. Our results suggest that one-loop bispectrum computations can play an important role in advancing kSZ cosmology.
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Cosmology and Nongalactic Astrophysics
Using the Circumgalactic Medium of Dwarf Galaxies as a Calorimetric Dark Matter Detector
Abby Mintz, Digvijay Wadekar and Romain Teyssier
Many well-motivated dark matter (DM) scenarios, including dark
photon DM,
axion-like particles, sterile
neutrinos, and primordial black holes, can deposit energy into ordinary matter and significantly raise the thermal energy of astrophysical gas. We present a simple, model-independent implementation of DM-induced heating in the RAMSES hydrodynamic simulation code, parameterized by an effective local heat-transfer rate $\Gamma_{\rm heat}$. Using simulations of an isolated gas-rich dwarf
galaxy with properties similar to WLM, we find that DM heating substantially alters the thermal structure of the circumgalactic medium (CGM) while leaving the
star formation rate and the dense ISM nearly unchanged. For $\Gamma_{\rm heat} = 10^{-27}$ to $10^{-25}\ {\rm s}^{-1}$, the neutral hydrogen column at 10 kpc is suppressed by 0.6 to 3.9 dex relative to the control simulation. Similarly, the C II and Si II column densities decrease by 4.1 and 5.5 dex, and by 2.2 and 3.0 dex for C IV and Si IV. These signatures are accessible to
quasar absorption-line spectroscopy, so CGM observations of nearby field dwarf
galaxies provide a promising avenue for constraining dark matter models that inject heat into ordinary matter.
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Instrumentation and Methods for Astrophysics
Automatic astrometric calibration of low-cost all-sky cameras
J. R. González Fernández, Laura Hermosa Muñoz, María Fernández Alonso et al. (+1 more)
All-sky cameras support weather monitoring, amateur astronomy, fireball and space-debris detection, and measurements of light pollution. These applications require reliable astrometric calibration despite imperfect camera
alignment and variable observing conditions. We present an open-source procedure that combines a compact fisheye model, an exact rotation to account for camera tilt, and automatic
star matching. It can initialise a calibration from a single frame given the observing site coordinates and observation time. We evaluate the procedure on nine cloud-free, moonless frames, obtained with a Raspberry Pi camera and a 1.55 mm lens. Fitting on eight frames and evaluating on the ninth in turn gives a median residual of 0.70 px (95% interval 0.64-0.80 px) across 4172 matches, reduced to 0.60 px by two optional decentering parameters. All nine single-frame calibrations pass the quality criteria and predict positions on other frames with a median residual of 0.78 px, taking about six seconds per calibration. We also apply the clear-sky calibration to 73 frames with varying lunar illumination or cloud cover, obtaining comparable residuals for accepted matches on moonlit frames (0.62 px). These results support reusing a calibration while the camera geometry remains unchanged and enough
stars remain visible for reliable matching. The procedure is available as the Python package ascal.
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All authors J. R. González Fernández, Laura Hermosa Muñoz, María Fernández Alonso, Lucía González Cuesta
High Energy Astrophysical Phenomena
Iron Nuclei with Energy of 10^19 eV in Extragalactic Cosmic Rays Near Earth
Anna Uryson
The paper discusses the fraction of extragalactic
cosmic iron
nuclei with energies of 10^19 eV that reached Earth from distant sources without fragmentation in intergalactic space. It is shown that the fraction of particles with energies E = 10^19 eV is significant (about 10%), even if the
redshifts of the sources reach 0.2, and not only for nearby sources.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Hadrophilic inelastic freeze-in dark matter in $q_1-q_2$ gauge extension and the high energy LZ event
Xiao-Gang He, Xuan Hong and Sk Jeesun
The recent observation of a single event at nuclear recoil energy $248\pm23\pm23$ keV by the LZ collaboration has prompted dark matter (DM) model builders to explore new physics explanations. While most of the existing literature invokes an endothermic scattering by a TeV-scale DM to explain the event, the favored DM interaction strength is in tension with the indirect detection constraints for most of the models. To evade this, this work explores exothermic DM scattering in a hadrophilic $q_1-q_2$ gauge extension setup with a new $Z'$
boson as a mediator to the dark sector. This can naturally escape the indirect searches in the absence of tree-level coupling of the mediator to
neutrinos, $W,\tau$, and $b$
quark. We consider freeze-in production at a low reheating temperature to populate DM in the early universe, with a comparatively smaller coupling than the thermal freeze-out scenario. We identify the $Z'$ parameter space that can explain the observed relic density and LZ event simultaneously. We also discuss the relevant constraints coming from flavor mixing and FCNC.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.optics
Setup and performance of focal-plane characterization benches for high precision astrometry
Fabrice Pancher, Sebastien Soler, Fabien Malbet et al. (+7 more)
Detecting Earth-like
exoplanets requires micro-arcsecond astrometry, which relies on a precisely calibrated focal plane equipped with high-resolution detectors. Accurate calibration depends on characterizing detector imperfections and systematic effects. Optical benches have been developed to assess the sensor's behavior: an integrating-sphere setup for electro-optical parameters, an interferometric bench for pixel-level geometry, and a
star-field projection system for intrinsic distortion. This work presents the characterization benches built for a 46-Megapixels (MP) imaging sensor, based on the same technology as the four 220-MP detectors foreseen for the final focal-plane, and the performance metrics obtained from these setups in the context of NASA's HWO and ESA's M-class missions. Upgrades will bring the test environment closer to operational conditions: a second 46-MP sensor will be added for multi-detector tests, plus an adjustable-angle fringeprojection system and improved
alignment.
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All authors Fabrice Pancher, Sebastien Soler, Fabien Malbet, Hugo Rousset, Manon Lizzana, Alain Leger, Thierry Lépine, Florence Ardellier-Desages, Jerôme Amiaux, Pierre-Olivier Lagage
High Energy Astrophysical Phenomena
Compelling evidence of a link between the lags of the quasi-periodic oscillations and the radio jet in the black-hole X-ray binary GRS 1915+105
Candela Bellavita, Mariano Méndez, Federico García et al. (+5 more)
GRS 1915+105 is one of the most studied black-hole X-ray binaries, known for its extreme variability and rich phenomenology. Previous studies of this source with the Rossi X-ray Timing Explorer reported a transition of the phase-lags of type-C quasi-periodic oscillations (QPOs) from soft, where low-energy
photons lag the high-energy ones, when the QPO frequency is higher than ${\sim} 2 ~{\rm Hz}$, to hard when the QPO frequency decreases below ${\sim} 2 ~{\rm Hz}$. The hard-lags of the QPO coincide with episodes of strong
radio emission. We analyse NICER observations of GRS 1915+105 obtained between 2018 and 2020, during a period in which the source flux decreased steadily, and perform a detailed spectral-timing study of the detected type-C QPOs. We find a type-C QPO with frequencies in the range of ${\sim} 1.3$-$3.9 ~{\rm Hz}$, which displays soft lags and, contrary to the RXTE observations, shows no evidence of hard phase lags at frequencies below $2~{\rm Hz}$. Quasi-simultaneous AMI-LA
radio observations show consistently low
radio flux (${\lesssim} 5 ~{\rm mJy}$) during this period. These results appear to show that the hard QPO lags in GRS 1915+105 are linked to the presence of strong
radio activity, suggesting that the relativistic jet is responsible for the hard phase lags, supporting a scenario in which QPO phase lags trace changes in coronal geometry and
accretion-ejection coupling in GRS 1915+105.
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All authors Candela Bellavita, Mariano Méndez, Federico García, Sara Motta, Pengcheng Yang, Wyncko Tonckens, Liang Zhang, Rob Fender
Solar and Stellar Astrophysics
Stellar activity in a post-merger Giant star
Hans Moritz Günther, C. Melis, K. J. Shen et al. (+3 more)
Binary
stars are the progenitors of exotic objects, such as
supernovae and gravitational wave sources. However, some systems merge earlier when the primary expands into a giant
star at the end of its lifetime on the main sequence and causes its companion to spiral in. TYC 4144-329-2 is a candidate post-merger first ascent giant
star with a circumstellar disk seen in the infrared (IR). We detect weak X-ray and far ultraviolet (FUV) emission from TYC 4144-329-2, which we interpret as a signature of weak coronal activity. We also find variability in Ha line profiles and in the optical light curves and we suggest an intermediate geometry where the line-of-sight passes through the upper layers of a flared disk with a time variable column density. While the X-rays must be coronal, the Ha line profiles point to ongoing and variable
accretion. We suggest that TYC 4144-329-2's merger was more recent than other
stars in this class and that it did not yet have time to develop a deep convection zone. If this scenario holds, TYC 4144-329-2 would be a unique probe of the earliest stages in the
evolution of post-merger systems.
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All authors Hans Moritz Günther, C. Melis, K. J. Shen, Eric G. Blackman, K. Hoadley, P. C. Schneider
Astrophysics of Galaxies
Constraining the Delay Time Distribution of the r- and s-Process from Stellar Ages at Solar Metallicity
Meng Zhang and Hans-Walter Rix
We present a new approach to constraining the delay time distribution (DTD) governing r- and s-process element production. Rather than using
metallicity as a proxy for time, we work directly with stellar ages at solar
metallicity, where chemical
equilibrium models are most applicable. We analyze two complementary samples: more than $10,000$ red clump (RC) thin disk
stars at solar
metallicity from LAMOST, and solar twins with high-precision abundances; both have well-determined stellar ages $\tau$. We fit chemical-
equilibrium models with power-law DTDs to the
evolution of [Eu/Mg]$(\tau)$ and [Ba/Mg]$(\tau)$ in each sample, taking europium as a canonical r-process element and barium as an s-process element, each referenced to magnesium as a near-instantaneous, CCSNe-dominated element. To validate the method, we first apply it to [Fe/Mg]$(\tau)$ and recover that $\approx\!70\%$ of Fe comes from a delayed channel with a declining DTD $\propto t^{-1.2}$, in agreement with well-established results for iron production in thermonuclear
supernovae. It also shows that about $60\%$ of Eu and Ba forming today originate from strongly-delayed processes, and the inferred delayed-production rates of both Eu and Ba rise with delay time, opposite to that of thermonuclear
supernovae. These results provide direct temporal constraints on r- and s-process enrichment, complementary to
metallicity-based chemical-
evolution studies. Because we model abundance referenced to Mg, and the same trend is recovered across
stars of different guiding-center radii, this appears unaffected by radial migration and chemical
evolution varying with Galactocentric radius. If confirmed, it points to delayed
neutron-capture production beyond NS–NS mergers.
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Instrumentation and Methods for Astrophysics
Calibrations for high precision differential astrometry onboard Theia and HWO
Manon Lizzana, Fabien Malbet, Hugo Rousset et al. (+3 more)
Future space astrometry missions such as Theia and an astrometric mode of the Habitable Worlds Observatory (HWO) require detector calibration and instrumental characterization at an unprecedented level to achieve sub-micro-arcsecond precision. This work presents three complementary developments addressing these requirements. First, we report an independent characterization of the GIGAPYX-4600 back-side illuminated CMOS detector, evaluating its linearity, readout noise, dark current, pixel response non-uniformity, defective pixel fraction, and inter-pixel capacitance. The results demonstrate excellent detector performance and confirm its suitability as a candidate for future gigapixel focal planes. Second, we develop an interferometric calibration method based on Young's fringes to measure pixel centroid displacements, enabling the characterization of inter-pixel response variations with an approach compatible with onboard implementation. The method is investigated through numerical simulations and an experimental testbed using the GIGAPYX-4600 detector. Finally, we introduce an astro-calibration framework that jointly estimates stellar astrometric parameters,
telescope attitude, plate scale, and optical distortion through a global iterative optimization. Although this calibration approach is still under development, simulations and laboratory activities are underway to validate its performance. Together, these developments contribute to the technological and calibration framework required for the next generation of high-precision astrometric space missions.
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All authors Manon Lizzana, Fabien Malbet, Hugo Rousset, Sébastien Soler, Fabrice Pancher, Éric Thiébaut
Astrophysics of Galaxies
The Multiphase CGM in the Epoch of Reionization: CII and CIV absorbers around [OIII] Emitters
C. Piscitelli, V. D'Odorico, M. Galbiati et al. (+17 more)
We investigate the multiphase circumgalactic medium (CGM) during the Epoch of Reionization (EoR, $z>6$) by cross-correlating cool- CII and warm-ionized CIV absorption systems with
star-forming [OIII] emitters. JWST/NIRCam wide-field slitless spectroscopy from the EIGER survey is combined with medium- and high-resolution optical/NIR spectra of six background
quasars, including new VLT/X-Shooter observations of PSO J159-02. We analyze the relation between 16 CII and 14 CIV absorbers ($\log(N) > 13.0$) and 136
galaxies, within an impact parameter of R$_{\perp} \leq$ 1000 pkpc and a line-of-sight separation of $\Delta v \leq 500$ km/s. We detect a statistically significant excess of both ions around
galaxies compared to a randomized background. We observe that the CIV covering fraction remains enhanced up to $\sim 1$ pMpc, whereas CII drops to the background level beyond $\sim 0.5$ pMpc, demonstrating that the warm-ionized phase is more spatially extended than cooler gas. Jointly, the 3D
galaxy-absorber spatial clustering is significantly weaker than the
galaxy-
galaxy auto-correlation. This provides direct physical evidence that early carbon enrichment is not confined to the virial radius of massive
star-forming systems; rather, a substantial fraction of these metals permeates the diffuse intergalactic medium (IGM) or is injected by a widespread population of faint, undetected dwarf
galaxies. Finally, we note a rapid radial decline of the CIV covering fraction compared with lower
redshift samples at $z<2$ and $z\sim3-4$ pointing out an evolving CGM ionization structure where early metals reside predominantly in lower ionization states. In conclusion, we determine a conservative lower limit for the observed carbon mass of $\rm M_{CII + CIV} \geq 2.8 \times 10^6 \, M_{\odot}$ within 300 pkpc.
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All authors C. Piscitelli, V. D'Odorico, M. Galbiati, M. Bischetti, G. Cupani, R. Dutta, S. Cantalupo, S. Di Stefano, S.T. Guida, K. Knudsen, C. Mazzucchelli, L. Paquereau, L. Pentericci, R. Rana, F. Ricci, F. Salvestrini, A. Tortosa, A. Travascio, C. Vignali, L. Zappacosta