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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 22 June

Instrumentation and Methods for Astrophysics

ffortissimo: A Freeform Forward-Modeling Pipeline for High-Contrast Images of Circumstellar Disks Based on Automatic Differentiation

Jay K. Kueny, Joseph D. Long, Jared R. Males et al. (+16 more)

Modeling circumstellar disks in the traditional sense carries the assumption that the dust density distribution can be accurately described with a fixed parametric form. Furthermore, commonly-used algorithms for subtracting the stellar point-spread function (PSF) distort the true morphology of the faint underlying disk structure, especially dusty features that are located at small angular separations. These phenomena often lead to significant residuals with parametric disk models and make it difficult to measure the full realizable range of the scattering function of the dust. We address these challenges with ffortissimo, a novel, pixel-based freeform forward modeling pipeline designed to characterize extended objects in KLIP-reduced images. We built this pipeline within the framework of JAX, which is a machine learning library in Python that enables efficient optimization through automatic differentiation ("autodiff") and GPU-accelerated array computations. Using visible light images of the disk around HR 4796A taken by the "extreme" Magellan Adaptive Optics instrument (MagAO-X), we show that our data-driven freeform models excel at fitting a complex dust distribution and can infer the dust scattering properties even through PSF subtraction artifacts. Additionally, we demonstrate the potential for retrieving spatial dust features beyond the diffraction limit of the telescope. We note that there are remaining challenges to address before precision photometry using these freeform models is advised. These include better background, wind-driven halo, and speckle characterization as preventing the freeform models from learning these noise artifacts is currently difficult.
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All authors Jay K. Kueny, Joseph D. Long, Jared R. Males, Alycia J. Weinberger, Laird M. Close, Joshua Liberman, Sebastiaan Haffert, Eden McEwen, Maggie Y. Kautz, Olivier Guyon, Logan Pearce, Parker T. Johnson, Katie Twitchell, Jialin Li, Alex Hedglen, Avalon Gower, Warren Foster, Jhen Lumbres, Lauren Schatz

High Energy Astrophysical Phenomena

TeV-PeV Gamma-ray and Neutrino Emission in the Galactic Plane

Saikat Das, Nayantara Gupta and Siyao Xu

We model the LHAASO observation of diffuse TeV–PeV $\gamma$ rays in the Galactic plane as the sum of unresolved leptonic emission from pulsar wind nebulae and hadronic emission from supernova-injected cosmic-ray (CR) protons. We investigate uncertainties in the radial distribution of the infrared component of the interstellar radiation field (ISRF), using profiles with enhanced photon densities in the inner Galaxy. We quantify their effects on $\gamma\gamma$ attenuation of the diffuse $\gamma$-ray emission. The alternative ISRF models affect the LHAASO diffuse fit only modestly, as the analysis excludes the Galactic center direction and applies source masks in the Galactic plane. Using the hadronic normalization inferred from the LHAASO fit for various ISRF models, the associated $pp$ neutrino emission remains consistent with the IceCube all-sky measurement, while the flux from the Galactic Ridge region remains compatible with current ANTARES and KM3NeT constraints. Since the modified infrared profiles differ most strongly toward the inner Galaxy, we also examine their impact on inverse-Compton emission from point sources near the central molecular zone. These same models can noticeably modify the hadronic and inverse-Compton $\gamma$-ray emission above $\sim\!10$ TeV from sources in the central region. Future KM3NeT observations, combined with $\gamma$-ray measurements of individual sources, can probe the inner-Galaxy CR population and constrain the radial distribution of the ISRF near the Galactic Center.
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High Energy Astrophysical Phenomena

Neutron Star Mass-Radius Constraints for EXO 0748$-$676 from 2008-2025 Quiescent X-ray Spectra

Mingyang Wang, Guobao Zhang and Ang Li

We present new constraints on the mass and radius of the neutron star in the neutron star low-mass X-ray binary EXO 0748$-$676 obtained from a joint analysis of 20 quiescent X-ray observations obtained between 2008 and 2025, including 14 Chandra and 6 XMM-Newton exposures. These data sample two quiescent episodes separated by the 2024$-$2025 outburst. We model the 0.5$-$10 keV spectra with a hydrogen-atmosphere model, assuming a source distance of 7.1 kpc. In a global Markov Chain Monte Carlo analysis in which the hydrogen column density, neutron star mass, and radius are tied across all observations, we obtain a neutron-star mass of $1.77^{+0.17}_{-0.22}\,M_\odot$ and a radius of $12.62^{+0.56}_{-0.74}$ km ($1\sigma$ credible intervals). We further perform independent fits to the first and second quiescent epochs and find that the combined data set significantly reduces the low-mass tail in the posterior distribution, leading to tighter lower bounds on the neutron-star mass. Incorporating the distance uncertainty of $7.1\pm1.2$ kpc, we conservatively constrain the neutron-star mass and radius to $M\simeq 1.41-2.11~M_{\odot}$ and $R\simeq 10.15-15.13$ km, favoring relatively stiff dense-matter equations of state. We also trace the thermal evolution across two quiescent epochs and find evidence for renewed crust cooling following the 2024$-$2025 outburst, providing a unique opportunity to compare the thermal relaxation behavior after two distinct accretion episodes.
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Solar and Stellar Astrophysics

Phase-mixing of acoustic waves: From the solar tachocline to marine vessel hydroacoustics

D. Tsiklauri

We adapt the magnetohydrodynamic wave phase-mixing paradigm [Tsiklauri et al. (2003)] to investigate harmonic wave, Gaussian pulse, and hyperbolic pulse propagation and damping in media governed by transverse sound speed gradients. This universal mechanism is applied to two distinct problems using the harmonic wave phase-mixed solutions. First, we resolve the 26-year-old helioseismic mystery of low-degree global $p$-mode linewidth anomalies observed by BiSON above $\nu \approx 3000\,\mu\text{Hz}$, demonstrating that a localised, non-turbulent sound speed gradient in the solar tachocline shear zone acts as the necessary high-efficiency energy sink. Second, we translate this formalism into a terrestrial metamaterial fluid engineering design. We show that an engineered microstructured mesh or stern cowl generating a controlled radial sound speed gradient induces severe near-field phase-mixing. This collapses the traditional bulk viscous damping length of $100\text{-kHz}$ propeller acoustic signatures from several kilometres down to a practical design envelope of approximately $10\text{ metres}$, providing an actionable paradigm for compact stealth shielding. Finally, as an independent theoretical extension, we establish a new power-law scaling governing a hyperbolic secant-squared pulse evolution: under developed-stage phase-mixing, its peak wave envelope decays as $\max(P_1) \propto x^{-9/2}$.
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Solar and Stellar Astrophysics

Stellar winds of O-type stars traced by high ionization fine-structure emission lines with JWST/MIRI

Calum Hawcroft, David R. Law, Linda J. Smith et al. (+8 more)

We investigate the presence of high ionization fine-structure emission lines across a range of 22 OB-type stars observed with JWST-MIRI as part of calibration programmes and the WISCI and MEAD projects. MIR wind emission is detected in 4 late O-dwarfs (O8 V - O9 V), 1 early O-dwarf (O5 V) and there are tentative detections in an additional 3 stars (O8.5 II, O8.5 IV and O9 I). We measure the wind speeds and make estimates of lower limits on the mass-loss rates of 5 O-type stars from broad, flat-topped emission in the fine-structure line of [Ne V] 14.3micron. We find terminal wind speeds that are generally in agreement with empirical trends, but note that in some cases the wind speeds are surprisingly low. We highlight two main takeaways from this sample, which combine to establish an exciting new window into the winds of massive stars. First, a new diagnostic ability is gained from lines formed at much higher ionization, larger spatial extent, and longer wavelengths than typical wind diagnostics. Secondly, there is frequent incidence of MIR emission in O-type stars, even in the 'weak-wind' regime where wind emission is often not detected in the UV and optical.
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All authors Calum Hawcroft, David R. Law, Linda J. Smith, Alexander W. Fullerton, Karl D. Gordon, Paul A. Crowther, Marjorie Decleir, Sascha T. Zeegers, Christiana Erba, Richard Ignace, D. John Hillier

Solar and Stellar Astrophysics

Phase-space averaging for stellar convection II. Maximum-entropy closures for mixed radiative-convective envelopes

P. S. Houdayer and M. Rieutord

Surface convection in cool stars sets the entropy jump between the atmosphere and the deep convective envelope, and therefore affects the radius and structure of one-dimensional stellar models. In standard local treatments, this entropy jump is controlled through an effective convective efficiency. We develop a phase-space closure that relates the mean stratification to the local distribution of entropy and velocity among convective elements. Our aim is to describe how the surface entropy transition emerges from the statistics of these elements, rather than prescribing it directly. We first construct a maximum-entropy model for the convective bulk, assuming that the realised states are bounded by a deep entropy level $S$. This maximum-entropy construction predicts a one-sided exponential entropy distribution, and its low-entropy tail is recovered in the deep convective part of the three-dimensional radiation-hydrodynamics simulations. Closer to the surface, the distribution is reorganised by radiative cooling and separates into two thermodynamic components. Using a radiative entropy branch, an adiabatically descending cooled branch, and a population fraction controlled by optical depth, the two-population closure reproduces the mean entropy stratification of the four reference simulations over most of the displayed range, without adjusting the entropy profile itself. The surface transition can therefore be interpreted as a continuous population decomposition, rather than as a sharp boundary between radiative and convective layers. This provides a natural route toward one-dimensional stellar models in which the surface entropy jump is determined from the statistical organisation of the flow instead of being set by a calibrated mixing-length efficiency.
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Solar and Stellar Astrophysics

Phase-space averaging for stellar convection I. Liouvillian dynamics

P. S. Houdayer and M. Rieutord

Convection remains one of the main uncertain links between multidimensional hydrodynamics and one-dimensional stellar evolution. In particular, transition regions such as near-surface layers or convective boundaries require mean-field descriptions that remain connected to the underlying dynamics rather than to a prescribed mixing length. We describe the flow as a distribution of mesoscopic fluid particles in position-velocity space. A conservation law for this distribution defines the average and yields the Reynolds-Favre mean-field equations as velocity-space moments. Under standard interior conditions, the same dynamics can be written in Liouvillian form, which extends the Hamiltonian structure to stratified and dissipative media. The Liouvillian formulation identifies the phase-space divergence, $\{s, T\}$, as a local measure of contraction or expansion of nearby trajectories. In the quasi-adiabatic limit, its sign reduces to the classical Schwarzschild stability criterion. Away from this limit, the diagnostic remains velocity-resolved and can distinguish different parts of the convective population within the same layer, for example in surface and penetration regions. Appendices show how rotation, magnetic fields, and composition changes can be incorporated through modifications of the phase-space structure. Phase-space averaging provides a dynamically grounded route from hydrodynamics to mean-field stellar convection equations. It also supplies a local trajectory-based stability diagnostic and a natural starting point for the maximum-entropy closures constructed in the companion paper.
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Solar and Stellar Astrophysics

New assignments of the CaH $A^{2}\Pi-X^{2}\Sigma^{+}$ transitions in the sunspot umbral spectrum and effective temperature estimation using molecular lines

Kosei Usami, Kaori Kobayashi and Hiroyuki Maehara

High-resolution spectroscopy observations of sunspots offer a unique natural laboratory for detailed molecular spectroscopy. Calcium monohydride (CaH) is a vital spectroscopic tracer in cool stellar and solar environments, where its electronic transitions are used for line identification and temperature diagnostics, yet its high-excitation transitions remain poorly characterized. Using high-resolution sunspot umbral spectra obtained with the Brault Fourier-transform spectrometer at the McMath-Pierce telescope (Wallace et al. 1999), we investigated the $A^2\Pi\;-\;X^2\Sigma^+$ electronic transition of CaH in the $\rm{14400-14900\;cm^{-1}}$ region. We report the assignment of 224 spectral lines spanning vibrational bands with $v^{\prime}, v^{\prime\prime} = 0\text{-}3$; notably, 75 lines in the (3-3) band are reported here for the first time, and the identification of the remaining bands was extended to significantly higher rotational quantum numbers ($J\rm{ _{max}\approx 49.5}$) compared to previous studies. Incorporating these new identifications into spectral simulations that account for overlapping TiO features, we aimed to reproduce the observed umbral spectrum and found modest but measurable improvement in the agreement between the simulated and observed spectra. Minimizing the residuals between observed and simulated spectra, we estimated an effective umbral temperature range of around 4000 K. We compare this effective temperature against those inferred from independent methods to show that molecular features primarily form in the cool umbral cores of the sunspots. This study demonstrates the utility of solar observations in studying the high-energy transitions that are challenging to reproduce in laboratory settings and the potential of molecular lines as sensitive "thermometers" for cool astronomical objects.
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Solar and Stellar Astrophysics

A $\lambda=1.3$ millimeter Survey for Disks around Herbig Be Stars

David J. Wilner, Joshua Bennett Lovell, Sean M. Andrews et al. (+3 more)

We present a survey of 24 Herbig Be stars (young stellar objects $>3$ M$_{\odot}$) within 3 kpc at 1.3~millimeters using the Submillimeter Array at about $1''$ resolution to identify circumstellar disks and assess planet forming potential. We detect 1.3 mm emission toward 5 Herbig Be stars that range in mass from 4.3 to 12.9 M$_{\odot}$. Follow-up observations at 0.87 mm show spectral indices consistent with partly optically thick dust emission. These millimeter detections are compatible with an extrapolation of the scaling relation derived for lower-mass T Tauri and Herbig Ae stars between millimeter luminosity and stellar host mass, and also millimeter continuum size, suggesting these detections represent emission from circumstellar disks. The implied disk masses are sufficient for giant planet formation. No decrease in the millimeter detection fraction with stellar host mass is evident within this sample that would implicate rapid disk dissipation by the radiation fields of the higher mass stars. The high fraction of millimeter non-detections is likely due to the survey sensitivity limits together with photoevaporation and the dynamical impact of stellar companions.
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All authors David J. Wilner, Joshua Bennett Lovell, Sean M. Andrews, Miguel Vioque, Feng Long, Luca Matra

Solar and Stellar Astrophysics

Detection of actinides in CEMP-rs stars

A. M. Riyas, D. Karinkuzhi, S. Van Eck et al. (+4 more)

The carbon-enhanced metal-poor stars with hybrid enrichments of slow- and rapid neutron-capture elements, the so-called CEMP-rs stars, still raise many questions due to their elusive abundance signatures. In our recent analysis, we found that heavy r process elements are enhanced in these objects and can be explained by the intermediate neutron-capture process (i-process) occurring in low-mass, very low-metallicity asymptotic giant branch (AGB) stars. However, the origin of actinides such as thorium and uranium is typically associated with explosive nucleosynthesis in highly neutron-rich environments, and their detection in stellar spectra remains challenging due to severe line blending from other elements and carbon-bearing molecules. In this work, we investigate the presence of thorium and uranium abundances in a sample of CEMP-rs stars using their high-resolution spectra obtained with the UVES spectrograph mounted on the UT2 (Kueyen) ESO VLT. Thorium is robustly detected in three stars, while uranium remains marginally detected, allowing only upper limits to be derived. Comparison with theoretical i-process nucleosynthesis models demonstrates that the observed abundances can be reproduced within uncertainties, supporting an i-process origin for these elements. This study reports the first detection of actinides in stars confirmed as CEMP-rs stars, providing new constraints on their nucleosynthetic history. Furthermore, these detections provide a potential way to estimate in the future the time elapsed since the proton-ingestion episode in AGB stars using cosmochronometry techniques, and more generally to place lower limits on the ages of the resulting white dwarf remnants.
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All authors A. M. Riyas, D. Karinkuzhi, S. Van Eck, A. Choplin, S. Goriely, L. Siess, A. A. Farha

High Energy Astrophysical Phenomena

Reverberation in the Narrow Fe K${\alpha}$ Line in the Seyfert Galaxy NGC 4151 with XRISM

Jon M. Miller, Aberahmen Zoghbi, Xin Xiang et al. (+11 more)

Emission lines that "echo" variations in the ionizing flux produced close to black holes are powerful probes of the central engine. In the Seyfert-1.5 galaxy NGC 4151, high-resolution X-ray spectra and time lags in low-resolution X-ray data suggest that part of the narrow Fe K$_{\alpha}$ line originates close to the optical broad line region (BLR). We report on a sequence of nine XRISM observations of NGC 4151, obtained every other day in 2024. Swift monitoring was undertaken to sample the driving flux before, during, and after the XRISM sequence. Using suitable line kernels, we measure a mean BLR component width of $\sigma = 5.36\pm 0.48\times 10^{3}~{\rm km}~ {\rm s}^{-1}$. Modeling the Swift continuum and XRISM line flux trends gives a lag of $\tau = 3.5^{+2.8}_{-1.7}$ days ($r=3.6^{+3.0}_{-1.7}\times 10^{3}~GM/c^{2}$ for $M_{BH} = 1.7\times 10^{7}~M_{\odot}$), significant at the $2\sigma$ level via Monte Carlo simulations, and consistent with prior measurements and direct spectral fits. This lag implies a black hole mass of $M_{BH}/f_{X} = 2.0^{+1.4}_{-1.0}\times 10^{7} M_{\odot}$, where $f_{X}$ is a geometrical factor. A standard optical value for this factor gives a mass that is nominally higher than typical H$\beta$ mass estimates, but formally consistent. Our results suggest that XRISM can measure lags and black hole masses in both unobscured and obscured AGN.
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All authors Jon M. Miller, Aberahmen Zoghbi, Xin Xiang, Doyee Byun, Missagh Mehdipour, Liyi Gu, Ehud Behar, Laura Brenneman, Elisa Costantini, Luigi Gallo, Matteo Guainazzi, Peter Kosec, Takeo Minezaki, Stephane Paltani

Cosmology and Nongalactic Astrophysics

Field-level weak lensing cosmology with $60$ simulations using multifidelity simulation-based inference

Alex A. Saoulis, Kiyam Lin, Niall Jeffrey et al. (+5 more)

We perform a realistic KiDS-Legacy mock analysis with field-level neural compression and simulation-based inference using just 60 $N$-body simulations. The weak lensing shear field encodes substantially more cosmological information than standard two-point summary statistics such as the power spectrum. Field-level inference can fully exploit this information, but physical realism at the field-level requires very high-fidelity simulations. This poses a major challenge for simulation-based inference (SBI): accurate empirical density modelling and deep-learning-based neural compression require tens of thousands of training samples, but achieving physical realism at the field level makes each simulation extremely costly. We demonstrate that multifidelity SBI can alleviate this tension by substantially reducing the number of high-fidelity simulations needed for accurate cosmological inference. We pre-train neural inference models on realistic KiDS-Legacy-like shear mocks using fast log-normal GLASS simulations and fine-tune them on a small set of high-fidelity $N$-body simulations. We show that $60$ high-fidelity simulations are sufficient to obtain informative and well-calibrated cosmological posteriors, enabling at least an order-of-magnitude reduction in simulation cost for accurate field-level inference in a realistic setting.
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All authors Alex A. Saoulis, Kiyam Lin, Niall Jeffrey, Maximilian von Wietersheim-Kramsta, Davide Piras, Alessio Spurio Mancini, Ana M. G. Ferreira, Benjamin Joachimi

High Energy Astrophysical Phenomena

Galactic Cosmic Ray Transport in the Giant Circumgalactic Medium Halo

Chao-Ming Li and Andrew M. Taylor

Recent observations have revealed that the Milky Way is embedded in a massive circumgalactic medium (CGM) extending to several hundred kiloparsecs. Such an extended gaseous halo acts as both a reservoir of baryons and potentially as a confinement volume for Galactic cosmic rays (CRs). We investigate CR transport in this giant Galactic halo and compare its properties with those of conventional small-halo models. In the giant-halo scenario, the halo height is no longer a free parameter, but instead relates to the extent of the source region. We show that CR transport within the source region remains similar to that in small-halo models, while substantial differences emerge at larger distances. In the giant-halo scenario, CRs develop an extended approximately 1/r spatial tail and exhibit a broader age distribution than the small-halo case. This model is shown to be consistent with current secondary-to-primary CR measurements. We further find that uncertainties associated with Galactic gas distributions are comparable to those arising from nuclear spallation cross sections. These results suggest that the giant-halo model provides a physically motivated alternative to conventional small-halo models and may have important implications for diffuse gamma-ray and neutrino emission from the Galactic environment.
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Cosmology and Nongalactic Astrophysics

Wedge-avoidance Fisher Forecasts for Primordial Features from Dark-Ages 21-cm Power Spectrum and Bispectrum

Chen Zhang, Furen Deng, Yidong Xu et al. (+3 more)

The Dark Ages offer a uniquely clean window on primordial physics, making the redshifted 21-cm signal a promising probe of inflation models. Forecasts for interferometric 21-cm measurements must account for foreground wedge avoidance, which removes a substantial fraction of Fourier modes, and this effect is especially severe at high redshifts. We develop a wedge-aware Fisher framework in which this mode loss is propagated directly into the variances of the anisotropic 21-cm power spectrum and reduced bispectrum. As a case study, we apply the method to forecast constraints on two inflation models with different oscillatory features, a resonant model and a step model, for a lunar far-side array including thermal noise. Since these features affect both the power spectrum and the bispectrum, we apply wedge avoidance to both forecasts and compare their constraining power on oscillatory amplitudes in these feature models. We find that wedge avoidance reduces available Fourier modes significantly in both observables, leading to much weaker constraints on inflationary features. This framework is broadly applicable to 21-cm power spectrum and bispectrum forecasts across redshifts and is particularly useful in regimes where foreground wedge effect is severe, such as the epoch of reionization and the higher-redshift Dark Ages.
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All authors Chen Zhang, Furen Deng, Yidong Xu, Bin Yue, Yuewei Wen, Xuelei Chen

Earth and Planetary Astrophysics

The Barnard's Star Planetary System: Stability, Composition, and Evolution of Four Sub-Earth Exoplanets

Xander Byrne, Claire Marie Guimond, Amy Bonsor et al. (+3 more)

Barnard's Star is the nearest single star to the Sun (1.8 pc), and hosts four recently-discovered planets. The star also has well-characterized stellar abundances of important rock-forming elements, including Fe, Mg, and Si. For refractory elements like these, the planets have likely inherited similar bulk elemental abundance ratios to the star, facilitating modelling of their interior structures. We present here an analysis of the Barnard's Star planetary system on several fronts. We perform a detailed stability analysis of the system, ascertaining that all four planets likely have masses between 0.19 and 0.84 $M_{\oplus}$, and are likely tidally locked, whereas a 4:3 mean-motion resonance chain for the inner three planets cannot be ruled out. Using atmospheric evolution models, we show that the prospect of extant primary atmospheres is highly unlikely on any of the planets. Barnard's Star's abnormally high Mg/Si ratio and low Th/Mg ratio imply planetary mantles which (a) are rich in (Mg,Fe)O ferropericlase; (b) have less than half the water capacity as Earth; (c) generate about half of the radiogenic heating as Earth; and (d) are cool and unlikely to have outgassed secondary atmospheres. Our analysis of this system presents an accessible set of first steps for the study of other nearby exoplanetary systems, as well as sub-Earth planets which will be increasingly discovered over the coming years.
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All authors Xander Byrne, Claire Marie Guimond, Amy Bonsor, Haiyang S. Wang, Sophia R. Vaughan, James G. Rogers

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

Primordial Black Holes from Vector-Induced Curvature Perturbations Sourced by Primordial Magnetic Fields

Chang Han, Zu-Cheng Chen, Hongwei Yu et al. (+1 more)

Generating an appreciable abundance of primordial black holes (PBHs) requires a substantial enhancement of primordial curvature perturbations on small scales. In this work, we propose a new post-inflationary mechanism in which such an enhancement arises during a stiff, or kination, epoch. The mechanism is driven by metric vector perturbations sourced by the vector component of the electromagnetic stress-energy tensor associated with primordial magnetic fields (PMFs). Since these first-order vector modes remain approximately constant during kination, they act as persistent nonlinear sources for second-order scalar perturbations. We show that the resulting vector-induced curvature perturbations are amplified toward the infrared cutoff of the kination band and exhibit the characteristic scaling $\mathcal P_{\mathcal R}(k)\propto k^{-5}$. As a concrete realization, we consider PMFs generated in a Ratra-type magnetogenesis scenario and find that the induced curvature perturbations can produce PBHs with an abundance large enough to constitute a substantial fraction of the dark matter.
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All authors Chang Han, Zu-Cheng Chen, Hongwei Yu, Puxun Wu

High Energy Astrophysical Phenomena

When the black holes align: a subpopulation of aligned massive binary black holes observed via gravitational waves

Stefano Rinaldi, Charmaine Wong, M. Paola Vaccaro et al. (+4 more)

In this work, we investigate the features present in the joint primary mass and effective spin distribution of binary black holes without relying on specific modelling assumptions. We make use of non-parametric methods, flexible models capable of approximating arbitrary probability densities with minimal mathematical assumptions, applying it to the newly released GWTC-5.0. Our analysis supports, albeit with large uncertainties, the presence of at least two separate sub-population of binary black holes showing different effective spin distributions: one of them, preferring positive $\chi_\mathrm{eff}$ values, points towards the direction of systems formed in a non-spherically-symmetric, dynamical environment.
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All authors Stefano Rinaldi, Charmaine Wong, M. Paola Vaccaro, Elvir Mislimi, Otto A. Hannuksela, Samson H. W. Leong, Michela Mapelli

Astrophysics of Galaxies

The hidden variability of the torus in local Active Galactic Nuclei: 20 years of Chandra, XMM-Newton, and NuSTAR observations

Vittoria Elvezia Gianolli, Nuria Torres-Alba, Stefano Marchesi et al. (+9 more)

X-ray absorption variability in active galactic nuclei (AGN) provides key constraints on the structure and dynamics of the circumnuclear obscuring medium, the so-called torus. A fraction of nearby AGN, however, have been classified as non-variable in line-of-sight (LoS) column density based on limited temporal coverage. We present the first systematic study of a sample of 11 local (z $\leq$ 0.1) obscured (N$_{\rm H} \geq 10^{22}$ cm$^{-2}$) AGN, initially classified as non-variable. The sample is selected from the Swift-BAT 100-month catalog, and comprises 60 observations from Chandra, XMM-Newton, and NuSTAR, spanning timescales from days to nearly two decades. We simultaneously model all available spectra for each source adopting physically motivated torus models: X-skirtor, RXTorusD, and UXCLUMPY. This approach allows us to derive the global properties of the obscurer while tracking possible epoch-to-epoch variations in the LoS column density and intrinsic X-ray emission. We find that the original non-variable classification (based on only two X-ray observations) is frequently not robust: clear N$_{\rm H,LoS}$ variability is detected in half of the sample, whereas 7 out of 10 AGN require intrinsic flux variability, with the rest showing flux-N$_{\rm H,LoS}$ degeneracies. We also find that the probability of identifying absorption variability increases with the number of observations, and the largest column density changes preferentially occur on long timescales, consistent with absorption by extended, structured clouds on torus scales. These findings support a clumpy and dynamic obscuring medium as a common feature of nearby AGN and highlight the importance of long-term X-ray monitoring for accurately characterizing AGN obscuration.
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All authors Vittoria Elvezia Gianolli, Nuria Torres-Alba, Stefano Marchesi, Marco Ajello, Claudio Ricci, Isaiah Cox, Massimo Gaspari, Dhrubojyoti Sengupta, Ross Silver, Indrani Pal, Andrealuna Pizzetti, Xiurui Zhao

Astrophysics of Galaxies

Spatially resolved star formation history of Sextans dSph

Andrés E. Piatti

We present a spatially resolved archaeological reconstruction of the Sextans dwarf spheroidal (dSph) galaxy using deep DECam wide-field photometry and the PANCAKE CMD-fitting code. By analyzing the star formation history (SFH) and age-metallicity relationship (AMR) across four radial zones, namely: core, ring, outer body, and outskirts, we find that Sextans is a composite system formed through a minor merger approximately 13 Gyr ago. Our results reveal an inverse metallicity gradient: a primitive, metal-poor host (the current core) surrounded by a more massive, chemically evolved envelope ($\Delta$[Fe/H] $\approx$ -0.5 dex) introduced by the accreted satellite. We identify a distinct delayed onset of star formation in the ring at $\sim$ 13 Gyr, marking the merger event. While the core quenched early, star formation in the outer body and ring persisted until $\sim$9 Gyr, suggesting that the final cessation of activity was driven by environmental stripping during infall into the Milky Way halo. We propose a plausible scenario to reconcile the derived inverse metallicity gradient with the observed horizontal-branch (HB) morphology and reported Mg deficits. We suggest that the red HB dominance in the core reflects its ancient, $\alpha$-rich nature, while the blue HB in the outskirts represents an $\alpha$-poor, accreted component. However, we note that our CMD-derived [Fe/H] values are model-dependent inferences based on the total metal content $Z$. These findings suggest a non-monolithic assembly for Sextans, posing a testable prediction of a strong radial gradient in [$\alpha$/Fe].
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Earth and Planetary Astrophysics

Parametrizing the projected wind fields of ultra-hot Jupiters in thermal emission: an application to GCM spectra of WASP-76b

Joost P. Wardenier, Romain Allart, Georgia Mraz et al. (+5 more)

High-resolution thermal emission spectroscopy provides a powerful probe of atmospheric circulation in ultra-hot Jupiters (UHJs), with Doppler shifts encoding information about the 3D wind field across the planet disk. Retrieving these wind properties from phase-dependent emission spectra requires a forward model that is both physically motivated and computationally tractable. We present dopplerkernel, a new forward model that parametrizes the projected line-of-sight velocity field on the planet disk using four wind parameters (an equatorial jet speed $v_\mathrm{jet}$ and width $\sigma_\mathrm{jet}$, a source-to-sink flow speed $v_\mathrm{wind}$, and a flow convergence longitude $\varphi_\mathrm{sink}$) and constructs a broadening kernel via weighted kernel-density estimation. We apply this framework in a Bayesian retrieval to synthetic $K$-band emission spectra of WASP-76b generated from three 3D GCM outputs. Our retrievals successfully recover the equatorial jet in the drag-free GCM to within ${\sim}1$ km/s of the zonal mean and infer day-to-night wind speeds in good agreement with GCM averages at 1-10 mbar for all three drag regimes. We find that spectral resolutions of $R \sim 100{,}000$ offer an optimal trade-off: sufficient to resolve global wind features while avoiding spurious detections caused by model-data mismatches at higher resolution. Combining pre- and post-eclipse phases yields more reliable constraints than either alone, particularly on the orientation of the source-to-sink flow. Experiments with more complex weight functions reveal a degeneracy between the velocity field and the thermal weighting, cautioning against overparametrization. In conclusion, a parametric broadening-kernel model with a small number of physically interpretable parameters can accurately reproduce the phase-dependent line shifts, shapes, and strengths in UHJ emission spectra.
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All authors Joost P. Wardenier, Romain Allart, Georgia Mraz, Louis-Philippe Coulombe, Frédéric Genest, Vigneshwaran Krishnamurthy, Enola Quenet, Vincent Yariv

Cosmology and Nongalactic Astrophysics

A cross-calibration approach for polarisation-sensitive detectors in CMB experiments: application to LiteBIRD's polarisation angle calibration

A. Novelli, F. Piacentini, S. Micheli et al. (+102 more)

We present a cross-calibration algorithm that determines the relative calibration of detectors within the same frequency band of a CMB experiment. The method iteratively compares single-detector maps with frequency-band maps, and it can be applied to any calibration parameter that can be corrected through reprocessing of the instrument's data at the map level. This allows for validation and correction of calibration both before and after observations. We validate the pipeline by calibrating the polarisation angle of simulated sky maps from the upcoming LiteBIRD experiment. The cross-calibration algorithm has been tested both in the case of random miscalibration of each individual detector and in the case of rotation of entire detector wafers. In both cases, the cross-calibration algorithm converges to the correct value and we are able to identify and correct relative miscalibrations in the polarisation angle of each detector with arcminute precision. Absolute calibration can then be addressed either through ground-based measurements, or through the $E$-$B$ nulling technique. To assess compliance with LiteBIRD's systematics budget, we propagate the residual miscalibration uncertainties through component separation and tensor-to-scalar ratio ($r$) estimation pipelines using both parametric (FgBuster) and blind (HILC) methods. In both cases, the induced bias on $r$ remains well below the LiteBIRD maximum budget for systematics of $\delta r < 6.5\times10^{-6}$. This confirms that the cross-calibration method presented is suited for use in modern high-precision CMB experiments.
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All authors A. Novelli, F. Piacentini, S. Micheli, E. Allys, A. Anand, J. Aumont, A. J. Banday, R. B. Barreiro, N. Bartolo, S. Basak, A. Basyrov, A. Besnard, D. Blinov, M. Bortolami, T. Brinckmann, F. Cacciotti, E. Calabrese, P. Campeti, A. Carones, F. Carralot, F. J. Casas, J. Chandran, K. Cheung, M. Citran, L. Clermont, F. Columbro, A. Coppolecchia, F. Cuttaia, P. de Bernardis, T. de Haan, E. de la Hoz, M. De Lucia, P. Diego-Palazuelos, H. K. Eriksen, F. Finelli, C. Franceschet, U. Fuskeland, G. Galloni, M. Galloway, M. Gerbino, M. Gervasi, R. T. Génova-Santos, T. Ghigna, S. Giardiello, C. Gimeno-Amo, A. Gruppuso, M. Hazumi, S. Henrot-Versillé, L. T. Hergt, E. Hivon, H. Ishino, K. Kohri, L. Lamagna, M. Lattanzi, C. Leloup, F. Levrier, A. I. Lonappan, M. López-Caniego, G. Luzzi, J. Macias-Perez, V. Maranchery, E. Martínez-González, S. Masi, S. Matarrese, T. Matsumura, M. Migliaccio, M. Monelli, G. Morgante, L. Mousset, R. Nagata, T. Namikawa, P. Natoli, F. Noviello, L. Pagano, A. Paiella, D. Paoletti, G. Pascual-Cisneros, G. Patanchon, G. Piccirilli, M. Pinchera, G. Polenta, L. Porcelli, M. Remazeilles, A. Ritacco, M. Ruiz-Granda, Y. Sakurai, L. Salvati, J. Sanghavi, V. Sauvage, D. Scott, M. Shiraishi, G. Signorelli, R. M. Sullivan, Y. Takase, L. Terenzi, M. Tomasi, M. Tristram, L. Vacher, B. van Tent, P. Vielva, S. Vinzl, I. K. Wehus, G. Weymann-Despres, E. J. Wollack, M. Zannoni

Astrophysics of Galaxies

Modelling the diffuse continuum emission: the NLS1 Mrk 110

Michael R. Goad, Kirk T. Korista and Edward M. Cackett

We present detailed model diffuse continuum (DC) plus hydrogen emission line templates from a summation over a broad range in hydrogen gas densities. We address the effect of finite gas densities and the presence of weak higher-order emission-line transitions on the strength and location of the Balmer and Paschen jumps which act to shift the jumps red-ward of their respective vacuum wavelength positions and substantially soften the gradient of the jump. Our photoionisation model-based DC template favours a lower optical depth and lower electron temperature than traditionally employed for the Balmer continuum, directly impacting empirical estimates of the strength of UV FeII. Microturbulent velocities increase the emission-line – continuum contrast, suppressing the DC contribution and weakening the jump heights, though the spectral shape of the DC remains broadly similar. Even with these additional complexities, a spectral decomposition of the UV-Optical-IR spectrum of the NLS1 Mrk 110, which includes a substantial DC contribution (30-50% of the total light at 3600A), reveals a significant deficit in emission just longward of the Balmer jump. Interestingly, significant thermal DC emission acts to flatten the SED through the UV-optical, negating oft-employed intrinsic reddening. Our best fit 1000A - 3 micron model requires a black hole mass of $~10^{8}$ Msun, similar to that inferred when considering features in the H/He broad emission line profiles, that suggest the presence of gravitational redshift. Finally, we provide diagnostic plots that may assist the spectral modeler to construct a physically useful DC spectrum and quantify its contribution to AGN UV-optical spectra.
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Astrophysics of Galaxies · Cross-listed from hep-ph

Signatures of gravity-mediated dark matter interaction in theories with large extra dimensions

A. Clarke, V. V. Flambaum, M. Pospelov et al. (+1 more)

Dark matter particles that couple to the Standard Model only through gravity are usually regarded as inaccessible to laboratory detection. This expectation can change in theories with $n$ extra spatial dimensions, where gravity is enhanced at short distances and the potential scales as $1/r^{1+n}$. We reconsider the gravity-mediated dark matter (DM) interactions in Arkani-Hamed-Dimopoulos-Dvali (ADD) models with $n$ large extra dimensions. The cumulative exchange of the gravitational Kaluza-Klein (KK) modes leads to the effective strength of interactions with the Standard Model nucleons that scales as $m_pm_\chi M_*^{-4}$, where $ m_\chi$ is the mass of DM and $M_*$ is the fundamental $4+n$ dimensional mass scale. We confront this interaction with sensitivity achieved in the large Xe-based underground direct detection experiments and derive bounds on the $\{m_\chi,M_*\}$ parameter space that stretches all the way to $M_*\sim$ few TeV. We also address the indirect detection of scalar $\chi$ that can resonantly annihilate via the on-shell KK modes into the SM particles $W^\pm,Z,h$. The annihilation cross section for the process scales as $\langle\sigma v\rangle \sim m_\chi^nM_*^{-n-2}$, and stringent limits on the same parameter space can be derived from observations of high-energy galactic $\gamma$ rays.
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All authors A. Clarke, V. V. Flambaum, M. Pospelov, I. B. Samsonov

Earth and Planetary Astrophysics

Thermal and rotational effects of giant impacts during terrestrial planet accretion

Adriana N. Postema, Simon J. Lock and Sarah T. Stewart

Terrestrial planets likely experienced one or more giant impacts during their formation that inflicted large thermal, chemical, and rotational perturbations. The early states of terrestrial planets are expected to be dominated by the thermal and rotational outcomes of giant impacts, but critical parameters that control internal processes, such as the pressures and temperatures of core formation, are not fully understood. Here we present the results from a representative suite of collisions between Moon- to super-Earth-mass bodies using the SWIFT hydrocode and updated ANEOS equations of state, allowing more robust temperature calculations. Using these results and the HERCULES planetary structure code, we calculated the contributions from thermal energy, gravitational potential energy, and post-impact rotation on the pressure-temperature conditions of the core-mantle boundary (CMB). We derived scaling laws for the efficiency of impact heating, mantle-core heat partitioning, and CMB pressures and temperatures. We find that post-impact CMB pressures are generally lower than previously assumed, due to both thermal and rotational effects. Full mantle melting is common and a substantial fraction of mantle material is heated above the Fe-MgO solvus closure temperature for impacts with modified specific energies $Q_S>10^6$ J/kg, implying that a miscible layer could form close to the CMB for many giant impacts. The comparatively low internal pressures and large regions of metal-silicate miscibility after giant impacts have significant effects on the processes of core formation, and our work indicates that metal-silicate equilibration would occur near the CMB during later post-impact cooling, consistent with Earth's geochemistry.
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High Energy Astrophysical Phenomena

On the assessment of the disk truncation and detection of type-II-like bursts from the accreting millisecond X-ray Pulsar IGR J17062-6143

Aditya Sow Mondal, Mahasweta Bhattacharya, Swarnendu Jana et al. (+2 more)

We present a spectral analysis of the NuSTAR and NICER observations of the accreting millisecond X-ray pulsar IGR J17062-6143, performed in 2022. The source remained in the hard spectral state during these observations, with a luminosity of about $\sim$0.13-0.14 percent of the Eddington luminosity. The continuum emission of the NuSTAR spectrum is entirely dominated by a power-law component or by Comptonized emission of disc photons by a plasma with a high electron temperature ($\gtrsim100$ keV). The NuSTAR spectrum also reveals clear evidence of disc reflection, a broad Fe K line around 6-8 keV, and a Compton hump peaking at 20 keV, irrespective of the choice of the continuum models. Our spectral studies suggest a disk extending close to the neutron star surface ($\sim$6-20 $R_{\rm g}$) at low inclination angle ($\sim41$ degrees), as revealed by the self-consistent relativistic reflection model, relxill. In addition, we detected type-II-like bursts for the first time in the NICER observation of this source. Light curve profiles of type-II-like bursts exhibit different patterns, mostly associated with the so-called mode-0 and transition from mode-0 to mode-1 type-II bursts. The energy spectra of the persistent (pre-burst) and burst emission are well described by an absorbed Comptonization component, scattering disk- and blackbody-distributed photons, respectively, by a corona with a temperature of 1-3 keV. Although the origin of the type-II-like burst is not very clear, it has been possibly linked to disk-magnetosphere interaction of the accretion flow.
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All authors Aditya Sow Mondal, Mahasweta Bhattacharya, Swarnendu Jana, Biplab Raychaudhuri, Gulab C. Dewangan

Earth and Planetary Astrophysics

Resonance and Stochastic Dynamics of Interplanetary Dust

Minli Qiu and Phil Arras

We study the motion of dust particles inspiraling from distant dust reservoirs toward a close-in planetary system, including the combined effects of radiation pressure and Poynting-Robertson (PR) drag. As dust particles migrate inward, they can be trapped in mean motion resonances (MMRs) depending on the competition between the planet's gravity and PR drag. Our goals are to understand the conditions under which particles can be trapped in MMRs, the evolution in and eventual escape from resonance, and the fraction of dust particles which will hit the planetary upper atmosphere, seeding it with heavy elements. Low-order eccentricity expansions of the disturbing function break down, so we employ an exact, rapid-phase–averaged disturbing function to determine resonant equilibrium points and their stability. We derive analytic expressions for the growth rate of dissipative equilibrium points and confirm that librations are generically overstable in important low-order resonances such as $3\!:\!1$, $2\!:\!1$, and $3\!:\!2$, implying that resonant capture is ultimately temporary and dust particles escape over a wide range of planet masses and dust size. After resonance escape, the dust orbit is planet-crossing and its subsequent evolution is intrinsically stochastic, governed by repeated close encounters that produce random gravitational kicks. We develop an analytic, epicycle-based scattering model to derive the impact parameter distribution $P(b)$ and the resulting energy change distribution $P(\Delta x)$. Using these encounter distributions, we construct a Monte Carlo method that predicts the fractions of dust particles that collide with the planet, sublimate near the star, or are ejected. Comparison of the Monte Carlo calculations with orbit integrations shows good agreement across the cases studied.
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Astrophysics of Galaxies

RAD@home discovery of a bow-and-arrow radio galaxy tracing a ~560 kpc bow-shock structure in a multi-halo environment

Ananda Hota, Pratik Dabhade, Shubhrangshu Ghosh et al. (+9 more)

We report the RAD@home citizen science discovery of a unique bow-and-arrow-shaped radio galaxy (BAARG; RAD J104501.6+352852, z = 0.159) identified in LoTSS DR2. The source exhibits striking asymmetry: on the western side, a narrow jet feeds a sector-shaped emission region at ~115 kpc, extending backward to form a ~560 kpc arc-like structure; on the eastern side, the jet develops an S-shaped distortion extending to ~250 kpc, followed by a faint, offset tail reaching ~600 kpc. Our analysis shows that the host resides in a dynamically complex, multi-halo environment with nearby cluster-scale systems at similar redshifts. The observed morphology is consistent with interaction between the radio plasma and the surrounding medium, influenced by large-scale environmental gradients and bulk motions. The western structure is consistent with compression of radio plasma near a bow-shock-like feature, possibly linked to supersonic motion of the infalling host galaxy and its circumgalactic medium. This possibly represents one of the first instances in which morphology and environment together suggest signatures of infall- or shock-related processes; surveys such as LoTSS DR3 may reveal similar systems, offering new insights into the interplay between radio galaxies and their large-scale environments.
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All authors Ananda Hota, Pratik Dabhade, Shubhrangshu Ghosh, Pranim Limbo, C. Konar, Sagar Sethi, Souvik Manik, Aditya Sahasranshu, Sabyasachi Pal, Mitali Damle, Sravani Vaddi, Arundhati Purohit

Earth and Planetary Astrophysics

A decade of monitoring the HIP 41378's planetary system

S. Grouffal, A. Santerne, X. Dumusque et al. (+32 more)

Multi-planetary systems provide key constraints on planet formation and evolution, as their architecture encodes the dynamical history of planets formed within a common protoplanetary disk. However, the current population remains strongly biased toward compact, short-period systems, and only a limited number of such systems with measured masses and radii are known. HIP 41378 is an exceptional system hosting five transiting planets with orbital periods up to 1.5 years, including an ultra-low density planet HIP 41378 f. The outer transiting planets d and e remained poorly constrained with unknown periods and masses, leaving the system architecture only partially characterised. We present long-term monitoring of this target with high-precision radial-velocity (RV) instruments (HARPS, HARPS-N, HIRES, and ESPRESSO) and space-based photometry spanning 2015-2024. We detect RV signals for all the planets, confirming their orbital periods and constraining their masses. In particular, the RV data strongly favour an orbital period of Pd = 278 days for planet d and refine the orbital period of planet e to Pe = 393+3-5 days. We measure a new mass of Mf = 25 \pm 5 earth masses for HIP 41378 f, confirming its super-puff nature with a bulk density of 0.166+0.033-0.036 g cm3. We also confirm the planetary nature of HIP 41378 g, a non-transiting planet with a 63-day period, and determine its minimum mass. In addition, the RVs reveal a long-period signal, with P = 2602+468-433 days, which we attribute to the candidate planet HIP 41378 h, although a stellar magnetic cycle cannot be excluded. Finally, we investigate the system's dynamical architecture and resonant structure, assess its completeness by constraining additional undetected planets, and discuss the implications for the origin and internal structure of the remarkable planet HIP 41378 f.
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All authors S. Grouffal, A. Santerne, X. Dumusque, B. Akinsanmi, T. Guillot, N. C. Hara, A. Leleu, L. Malavolta, M. Saillenfest, D. J. Armstrong, S. C. C. Barros, D. Bayliss, A. S. Bonomo, D. J. A. Brown, A. Collier Cameron, M. Cretignier, I. J. M. Crossfield, F. Dai, M. Damasso, O. Demangeon, P. Figueira, P. Leonardi, A. F. Martinez Fiorenzano, M. Lopez-Morales, E. Molinari, A. Mortier, L. D. Nielsen, H. P. Osborn, E. Petigura, K. Rice, N. C. Santos, A. Sozzetti, S. Sulis, S. Udry, C. Watson

Astrophysics of Galaxies

Cold kinetic theory is not cold fluid theory: A collective mode in self-gravitating spheres

Mikael Tacu

Cold collisionless matter is usually described by pressureless fluid equations; this fails in three-dimensional spherical geometry. For the cold spherical case, kinetic and fluid descriptions share the same time-domain dynamics, but if we look at the spectrum, the kinetic system admits one solution the fluid does not: a discrete mode at twice the central orbital frequency, $\omega_0 = 2\Omega(0)$. It is specific to 3D: razor-thin disks reduce to the fluid description. Nonlinear simulations confirm it survives at finite dispersion. Around Sgr~A$^*$ it lies at $\kappa(r_{\rm in})$, with $r_{\rm in}$ the cusp's inner edge; if excited, stars at all radii would oscillate at this one frequency.
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Astrophysics of Galaxies

When bars and spirals conspire: recurrent build-up of the nuclear regions of disc galaxies

Tristan Boin, Sergey Khoperskov, Paola Di Matteo et al. (+6 more)

The assembly history of the central regions of disc galaxies is regulated by dynamical processes that trigger gas infall events, leading to active star formation in nuclear stellar discs (NSD) and in nuclear stellar clusters (NSC). In the Milky Way, recent studies of its nuclear regions have revealed a complex star formation history (SFH), with an initial burst associated to the formation of the Galactic bar, followed by a non-constant star formation rate. In this work, we aim to study the formation and evolution of nuclear structures and their link with the formation of large-scale structures. Our goal is to investigate the effects of the bar and spiral arms on the gas dynamics and, as a result on the SFH of NSDs and NSCs. We run a simulation of an isolated Milky Way-like galaxy with the SWIFT N-Body+hydro simulation code, including star formation and stellar feedback from SNIa & SNII. We start from a live DM halo and a pre-existing stellar & gaseous disc with 20% gas fraction, which form a bar, a boxy/peanut bulge, spiral arms and nuclear structures. We study the SFH of these regions and how they relate to variations in the bar length, strength and pattern speed. We investigate the role of spiral arms and their interaction with the bar. We find that the SFH of the nuclear regions display a main burst at bar formation time, due to bar-driven gas inflows. After bar formation, we find secondary periodic formation bursts, that do not appear in the disc SFH. These bursts occur when the spiral arms and the bar, rotating at different pattern speeds, reconnect, triggering secondary gas inflow events. The interaction of spiral arms and the galactic bar can enhance non-axisymmetric features in the disc, triggering bar-driven gas infall even after the bar has formed. These bar-spiral reconnection events are imprinted into the SFH of the NSCs and NSDs as episodic star formation bursts.
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All authors Tristan Boin, Sergey Khoperskov, Paola Di Matteo, Nils Hoyer, Alessandra Mastrobuono-Battisti, Nils Ryde, Françoise Combes, Mathias Schultheis, Misha Haywood