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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 10 August

High Energy Astrophysical Phenomena

Rapid Orbital Decay in the Ultracompact Double-degenerate Binary eRASSU J060839.5$-$704014

Rahul Sharma, Chandreyee Maitra, Frank Haberl et al. (+9 more)

We present timing and spectral analysis of the recently identified ultracompact double-degenerate (DD) white dwarf binary eRASSU J060839.5$-$704014 using observations from NICER and Einstein Probe (EP), together with archival XMM-Newton data. By phase-connecting the long-term XMM-Newton, NICER, and EP observations, we obtain a coherent quadratic timing solution, yielding an orbital period of 374.15013 (2) s and an orbital decay rate of $\dot{P}= -4.7\,(1) \times 10^{-11} \mathrm{~s~s^{-1}}$. This orbital decay exceeds that measured in the prototypical DD binaries HM Cnc and V407 Vul. Assuming that the observed orbital evolution is primarily driven by gravitational-wave (GW) angular momentum loss, the inferred chirp mass is $\sim0.43\, M_{\odot}$, placing the source among the most massive known systems of this class. The phase-averaged spectra of NICER and EP-Follow-up X-ray Telescope (FXT) are described by a soft thermal component with temperatures of ~126 and ~144 eV, respectively, confirming the supersoft nature of the source. Phase-resolved spectroscopy reveals a clear decrease in temperature across the bright phase in both instruments, indicating a structured emission region with significant temperature gradients. These results establish eRASSU J060839.5$-$704014 as one of the most rapidly evolving ultracompact DD binaries presently known, belonging to the rare class of direct-impact ultracompact binaries, and a promising verification source for future low-frequency GW studies.
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All authors Rahul Sharma, Chandreyee Maitra, Frank Haberl, Joheen Chakraborty, Susanne Friedrich, Yong-Feng Huang, Chichuan Jin, Zhaosheng Li, Georgios Vasilopoulos, Yanjun Xu, Haonan Yang, Weimin Yuan

Instrumentation and Methods for Astrophysics

Kratos-linerad: GPU-accelerated Monte Carlo radiative transfer of lines with efficient imaging

Lile Wang

Spectral lines encode the velocity, the temperature, and the chemical structure of astrophysical gas; interpreting them requires radiative transfer that is accurate at high optical depth, consistent with the local excitation, and efficient enough to synthesize velocity-resolved images. We present Kratos-linerad, a GPU-accelerated Monte Carlo radiative transfer code for spectral lines. The level populations can be iterated to statistical equilibrium together with the escaping photon distribution, treating angle-dependent partial frequency redistribution through constant-memory sampling tables. The code adopts the two-step imaging scheme to line transfer, in which a Monte Carlo pass samples a velocity-resolved scattering emissivity, and a deterministic ray-tracing pass synthesizes channel maps decoupled from the scattering geometry. Validation reproduces the analytic scaling of escaped spectra and the imaging double-peak profiles. GPU parallelism enables both stages sufficiently fast for routine application to astrophysically realistic models.
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High Energy Astrophysical Phenomena

Astrophysical origins of TeV features in the cosmic-ray lepton spectrum

Zhen Xie and Ruizhi Yang

Precise measurements of high-energy cosmic-ray electrons and positrons have revealed spectral structures that are difficult to capture with a single smooth power-law background. The rising positron fraction measured by PAMELA and AMS-02, together with the all-electron excess reported by ATIC and the high-precision all-electron spectrum measured by DAMPE, has motivated interpretations ranging from nearby astrophysical accelerators to dark-matter annihilation or decay. In this work we revisit the conventional diffuse electron background and the possible contribution from nearby pulsars in a common propagation framework. The diffuse component is modeled with GALPROP configurations calibrated by cosmic-ray nuclei and diffuse gamma-ray observations. We then use the Green-function solution for nearby discrete sources with radiative losses to study pulsar contributions with both burst-like and continuous injection histories, including the effect of stochastic inverse-Compton cooling on the propagated spectra. We also use the highest-energy DAMPE data points as an illustrative case to compare possible local-source contributions from pulsars and supernova-remnant-like burst sources. The spectral shape of such features provides a useful diagnostic for distinguishing physically plausible nearby-source features from more exotic interpretations.
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Instrumentation and Methods for Astrophysics · Cross-listed from math.NA

High-order fully discrete multi-entropy-stable and bound-preserving schemes for relativistic Euler equations

Linfeng Xu and Kailiang Wu

A discrete entropy inequality is the principal nonlinear stability estimate available for systems of conservation laws, and evaluating it presupposes a physically admissible state. So far, however, the two have been secured separately. Entropy-stable schemes are almost always semi-discrete, are built around one selected entropy pair, and take for granted the positivity of density and pressure that makes the entropy well defined in the first place, whereas bound-preserving limiters keep the solution admissible but deliver no entropy estimate. For the special relativistic Euler equations, the two cannot be separated at all, since the conservative-to-primitive map is implicit, and an inadmissible state therefore has no entropy to correct. Here we construct high-order discontinuous Galerkin and finite volume schemes that, to our knowledge, for the first time, are entropy stable in the fully discrete sense for an arbitrary prescribed finite family of convex entropy pairs, a property we call multi-entropy stability, and are provably admissible wherever an entropy is evaluated. All of this is achieved by a single cellwise projection, and neither conservation nor the design order is lost. The construction rests on relativistic causality, which bounds every characteristic speed by the speed of light. Consequently, the numerical viscosity can be fixed once for all states and all equations of state, and one two-point building block then serves the whole entropy family. Since only the convexity of the admissible set and this speed bound are used, the same route remains open for related systems. Finally, in computations with four equations of state, the schemes retain high-order accuracy close to vacuum, produce no inadmissible state in strong shocks, near-vacuum shock–vortex interaction or jets with Lorentz factor above $70$, and confirm the monotone decay of every enforced discrete entropy.
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Astrophysics of Galaxies

Active galactic nucleus activity in nearby disk galaxies: The roles of bar strength and spiral arm morphology

Zh. R. Martirosyan, A. A. Hakobyan, V. Adibekyan et al. (+3 more)

(abridged) We investigate the dependence of AGN activity on bar strength and spiral arm morphology in nearby spiral galaxies, with a particular emphasis on disentangling their individual and joint effects while controlling for galaxy stellar mass and color. We constructed a sample of 843 morphologically undisturbed Sa-Sd galaxies from the MaNGA survey in the redshift range $0.026 \leq z \leq 0.1$. Bar strengths, stellar masses, colors, and AGN classes were adopted from the literature, while spiral arm classes (ACs), i.e., flocculent (FL), multi-armed (MA), and grand design (GD) systems, were visually determined for the entire sample using optical imaging together with bulge-disk decomposition residual maps. The AGN fraction increases systematically with bar strength, from $0.10^{+0.02}_{-0.02}$ in unbarred galaxies to $0.34^{+0.03}_{-0.03}$ in strongly barred systems. After controlling for stellar mass and color, a statistically significant enhancement remains detectable primarily at intermediate stellar masses ($10.5 \lesssim \log(M_\star/M_\odot) \lesssim 11.0$), whereas no significant dependence is found at higher masses. In contrast, spiral arm morphology alone does not show a robust independent connection with AGN activity once stellar mass and color are controlled, although a weak enhancement is present in intermediate-mass GD and MA systems. When bar strength and spiral AC are considered jointly, the highest AGN fraction is observed in strongly barred GD$+$MA galaxies $(0.39^{+0.04}_{-0.04})$, while the lowest AGN fractions are found in unbarred FL systems $(0.09^{+0.03}_{-0.02})$. Our results suggest that stellar mass and color drive the primary trend in AGN activity in nearby disk galaxies, while stellar bars and spiral arms act as secondary structural drivers.
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All authors Zh. R. Martirosyan, A. A. Hakobyan, V. Adibekyan, L. V. Barkhudaryan, M. H. Gevorgyan, A. G. Karapetyan

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

Correlated parity violation in gravity and electromagnetism from five-dimensional spacetime

Haomin Rao, Yunlong Zheng, Qi-Zhe Hou et al. (+2 more)

Parity violation in the gravitational and electromagnetic sectors has been extensively investigated, yet the two are conventionally treated as independent phenomena. This separation, however, may be a four-dimensional prejudice. In higher-dimensional spacetime, gravity and electromagnetism may share a common geometric origin—and so, perhaps, does their parity violation. In this paper, we pursue this idea by constructing parity-violating Kaluza-Klein models in both Riemannian and teleparallel geometries. In Riemannian geometry, the simplest five-dimensional parity-violating term reduces to several complicated four-dimensional terms, including the familiar gravitational Chern-Simons term, which suffers from a ghost instability. In teleparallel geometry, however, the result is strikingly simple. The simplest five-dimensional parity-violating term reduces to only two ghost-free terms—the familiar Nieh-Yan term and the standard electromagnetic Chern-Simons term. Remarkably, the model predicts that the helicity-dependent dispersion shift for electromagnetic waves is exactly six times that for gravitational waves, $\Delta\omega^{2}_{ EM}=6\,\Delta\omega^{2}_{GW}$, a background-independent relation. This relation offers a falsifiable test of unification through joint cosmic microwave background and gravitational wave birefringence observations.
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All authors Haomin Rao, Yunlong Zheng, Qi-Zhe Hou, Jian-Wen Ou, Changyong Zhu

High Energy Astrophysical Phenomena

Impact of disk magnetic fields on the propagation of stellar-scale jets in the magnetically arrested accretion disks of active galactic nuclei

Bao-Quan Huang, Tong Liu and Jian-Fu Zhang

It is widely recognized that active galactic nucleus (AGN) disks host numerous massive stars and compact objects. Stellar-scale jets triggered by collapses of massive stars and mergers of compact objects could propagate through the disk and produce observable electromagnetic radiation. Magnetically arrested disks (MADs), supported by both numerical simulations and observations, possess strong magnetic fields (MFs). As jets travel within such environments, the MFs should regulate jet evolution and shape radiation signatures. In this work, we explore the effects of disk MFs on jet propagation and breakout emission within the MAD framework. We employ a jet-cocoon model that accounts for potential disk-MF effects, including both magnetic pressure and magnetic energy dissipation driven by magnetic reconnection. We find that magnetic pressure effectively suppresses the lateral expansion of the cocoon, which enhances jet collimation and modestly increases the jet-head velocity. Furthermore, magnetic pressure effects are more pronounced at relatively low jet powers. In this regime, the breakout luminosity of the jet-head shock is enhanced, while its breakout time is shortened. However, the magnitude of the luminosity enhancement is sensitive to the adopted regime-dependent emission prescriptions. These findings suggest that, within the explored parameter space, disk MFs can facilitate the breakout of low-power jets arising from binary black hole mergers in AGN MADs.
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Instrumentation and Methods for Astrophysics

Pointing Model Meets Deep Learning: A Retrospective Study on a MeerKAT+ Telescope Applying Deep Learning Methods for Blind Pointing Corrections

Stefan Thoms and Matthias Reichert

This study aims to compare the effectiveness of deep learning methods, specifically Feedforward Neural Networks (FNNs), with traditional Pointing Models (PMs) for compensating Blind Pointing Errors in astronomical instruments. Ambitious projects like the ongoing study for the Atacama Large Aperture Submillimeter Telescope (AtLAST) inspired the investigation of possible improvements to traditional Pointing Error (PE) modeling. The study assesses the practicality of FNNs by applying them to data from an instrument in operation: a precursor MeerKAT+ telescope from the Max Planck Institute for Radio Astronomy (MPIfR), intended to extend the current MeerKAT Radio Telescope Array at the South African Radio Astronomy Observatory (SARAO) site in the Meerkat National Park in South Africa.
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Earth and Planetary Astrophysics

Decoding Exoplanetary Degeneracies Through Geometry: Application to Asynchronously Rotating Systems

Mradumay Sadh

This study augments the geometry-based InstellCa code that calculates accurate irradiance values to InstellCa–2, which computes the longitude averaged instellation over a given latitude on the planet along with its effective temperature profile. The estimation of instellation is performed considering the planet as a 3D body that asynchronously rotates, causing a varying zenith angle of the star resulting in a diurnal cycle. This serves as a specialised case study to demonstrate how the combination of this relative rotation and extreme proximity to host-stars can affect the estimated effective temperatures of close-in planets. 55 Cancri e is selected specifically to demonstrate the importance of this effect as it has been earlier hypothesised to exhibit asynchronous rotation and also has a debated scientific discourse about the existence of an atmosphere on the planet. The TRAPPIST-1 system, being a multi-planetary system susceptible to mean motion resonances, also serves as an interesting exemplar case to demonstrate these effects. Incorporating the stellar zenith angle to the geometrical analysis allows the possibility of physically feasible Bond albedo values that would otherwise be prohibited if a synchronously rotating bare rock scenario is assumed. Consequently, the degeneracies in the modelling of different atmospheric states of such planets can be reduced if the correct geometry is taken into account.
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Instrumentation and Methods for Astrophysics

Optimizing Wavefront-Deformation Sensor Placement for Active Radio-Telescope Surfaces

Stefan Thoms, Martin Timpe and Matthias Reichert

Next-generation high-frequency radio telescopes require primary-surface accuracies that passive structures alone cannot reliably achieve. The Atacama Large Aperture Submillimeter Telescope (AtLAST), a 50 m single-dish concept operating up to $\approx$ 1 THz, imposes a $\approx$ 20 $\mu$m rms surface-accuracy requirement across its full aperture. This is practically unattainable for a purely passive reflector subject to gravitational, thermal, and wind-induced deformation. Closed-loop active collimation and surface control are therefore imperative, which in turn requires the deformation field to be known across the full aperture in real time. Measuring it directly at the necessary resolution across the complete surface is, however, hardly feasible; instead, the current AtLAST concept development foresees reconstructing the surface from a limited set of discrete sensor positions. An algorithmic framework is presented that optimizes the number and placement of these sensors to maximize the reconstructability of the deformation field. Finite-element analysis (FEA) load cases (gravity, thermal, wind) define the deformation space, from which a data-driven Proper Orthogonal Decomposition (POD) basis is derived; sensor positions are then chosen by a greedy optimization algorithm and then assessed via leave-one-out cross-validation. Applied to FEA deformations of AtLAST's Back-Up Structure (BUS), and assuming a sensor noise of 5 $\mu$m rms, the method reconstructs all load cases with 50 sensors to below 2.7 $\mu$m rms (worst case) residual (BUS-) surface error.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Hadron-quark phase transitions along proto-neutron-star evolution

P. Laskos-Patkos, P.S. Koliogiannis and Ch.C. Moustakidis

The new era of multi-messenger astronomy requires the accurate and self-consistent derivation of the nuclear equation of state at high temperature. In the present work, we focused on the calculation of hot hybrid equations of state, studying the different evolution stages of a proto-neutron star with a quark matter core (proto-hybrid star). For the hadronic matter we used two distinct Skyrme effective interactions, while for quark matter the well-known vector MIT bag model was employed. To model the era of trapped neutrinos in the system we considered the global conservation of lepton fraction which resulted in an equation of state with an extended mixed phase. For periods following the neutrino diffusion phase of a proto-neutron star, the equations of state were modelled using both the Maxwell and the Gibbs construction depending on the assumption for either local or global electric-charge conservation. With the use of the derived hybrid models, we solved the Tolman-Oppenheimer-Volkov equations to describe the corresponding hybrid star configurations. Finally, we investigated how the structure of proto-hybrid stars evolves, using constant rest mass sequences. We found that regardless of whether electric-charge is globally or locally conserved, the earlier stages of a hybrid star's life may play a crucial role on the determination of its maximum possible gravitational mass in later stages.
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Astrophysics of Galaxies

Statistical inference of fast radio burst environments using galaxy number density

Vignesh V.V. Rao, Tetsuya Hashimoto, Tomotsugu Goto et al. (+9 more)

Fast radio bursts (FRBs) are bright, millisecond-duration radio transients of unknown origin. They are categorized as repeaters and non-repeaters, possibly indicating distinct progenitor types. However, validating this distinction is difficult because of the limited number of localized FRBs. Large-scale galactic environments can provide insight into the nature of the host galaxies of FRBs and their progenitors. High-number-density regions are typically associated with old galaxies, whereas low-number-density regions are linked to young star-forming or less massive quiescent galaxies. In this study, we use galaxy number density to statistically assess the environments of 19 repeaters and 253 non-repeaters from CHIME Catalog 1, using galaxies from the WISE x PS1 catalog. A Kolmogorov-Smirnov (KS) test showed no significant difference between the two populations ($p_{\rm KS} = 0.673$). This result indicates that the statistical significance of the difference could depend on small-number statistics, highlighting the necessity of future FRB samples. Intriguingly, a comparison of FRBs with random galaxy fields suggests that FRBs may preferentially occur in underdense galactic environments, with a median $p$-value ($p_{\rm KS}$) of $2.84 \times 10^{-2}$ compared to random galaxy apertures.
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All authors Vignesh V.V. Rao, Tetsuya Hashimoto, Tomotsugu Goto, Shotaro Yamasaki, Mohanraj Madheshwaran, Sridhar Gajendran, Tomoki Wada, Simon C.-C. Ho, Terry Long Phan, Yuri Uno, Amos Y.-A.Chen, Hiroto Masaka

Instrumentation and Methods for Astrophysics

Foreground Subtraction with a Tensor-Based Oriented Singular Value Decomposition Method for HI Experiments

Shifan Zuo, Xuelei Chen and Yi Mao

We introduce a native tensor-based framework for foreground mitigation in 21\,cm intensity mapping (IM), utilizing the Oriented Singular Value Decomposition (O-SVD) algorithm. While 21\,cm IM is a powerful probe of the large-scale structure of the Universe, its efficacy is severely limited by astrophysical foregrounds that are orders of magnitude brighter than the cosmological signal. Traditional mitigation strategies often necessitate flattening multidimensional data cubes into two-dimensional matrices, a process that potentially compromises the intrinsic spatial-spectral correlations by treating distinct spatial pixels as independent samples. By treating multi-frequency sky maps and angular power spectra as third-order tensors, the O-SVD method performs decomposition directly on the multilinear manifold, preserving the underlying physical topology and leveraging the distinct coherence properties of astrophysical foregrounds across different dimensions. We demonstrate the performance and versatility of the O-SVD framework through its application to high-fidelity simulations from the SKA Science Data Challenge 3a (SDC3a) and real-world observational data from the Tianlai Cylinder Pathfinder Array. Our results indicate that O-SVD provides a robust and universal approach for foreground subtraction, achieving high-fidelity signal recovery while offering superior performance compared to conventional matrix-based Singular Value Decomposition (SVD) methods.
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Cosmology and Nongalactic Astrophysics

Multi-tracer mass bias in matched cosmic voids from SDSS DR7 and the ELUCID constrained simulation

Youcai Zhang, Xiaohu Yang, Hong Guo et al. (+1 more)

Cosmic voids provide a unique environment for studying the relationship between galaxies, subhaloes, and dark matter in the underdense Universe. Using the SDSS galaxy catalogue and the ELUCID constrained simulation, we establish an observationally anchored framework for measuring multi-tracer mass bias within matched cosmic voids. A sample of 102 matched void pairs is constructed to directly compare galaxy, subhalo, and dark matter mass distributions within an observationally constrained realisation of the local Universe. We find that both the galaxy-to-dark matter and subhalo-to-dark matter mass ratios decrease toward void centres, indicating that luminous and halo tracers become increasingly depleted relative to the underlying matter distribution in the deepest underdensities. In contrast, the galaxy-to-subhalo mass ratio exhibits substantially larger statistical uncertainties within the inner void regions ($r/R_{\rm v}\lesssim0.5$). By comparing measurements obtained using independent and common coordinate frameworks, we show that coordinate offsets contribute to the observed scatter but cannot fully account for the large uncertainties. The remaining uncertainty primarily arises from the severe scarcity of massive subhaloes ($\log_{10}(M_{\rm sub}/h^{-1}M_\odot)\ge11.8$) within void interiors, which greatly reduces the number of statistically valid measurements near void centres. Our results provide an empirical characterization of multi-tracer mass bias in observationally constrained cosmic environments and demonstrate the importance of accounting for coordinate consistency and tracer scarcity when interpreting such measurements in extreme underdense regions.
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All authors Youcai Zhang, Xiaohu Yang, Hong Guo, Peng Wang

Astrophysics of Galaxies

Unveiling Metal Mixing in a Grand-Design Spiral: A UV-optical multiphase spatially resolved study of M83

Adarsh Ranjan, Bethan L. James, Svea Hernandez et al. (+4 more)

We present a spatially resolved, multiphase study of chemical enrichment around young star clusters (YSCs) in the nearby grand-design spiral M83 by combining far-ultraviolet(UV) absorption-line spectroscopy from HST/COS with cospatial optical spectroscopy from VLT/MUSE and LBT/MODS. Our sample includes 18 YSCs spanning spectroscopic ages of ~1-6 Myr and galactocentric radii out to R/R_{25}=0.56. Neutral (H I) abundances were derived from UV absorption-line spectroscopy and compared with ionised (H II) abundances from reddening-corrected optical emission lines. Because auroral lines are not detected in all regions, we develop and apply an empirical multi-zone electron temperature (T_e) calibration based on strong-line diagnostics to estimate T_e and derive reliable nebular abundances. We measure oxygen(O), sulphur(S), nitrogen(N), and iron(Fe) abundance tracing enrichment from distinct nucleosynthetic channels. The alpha-elements (O and S) exhibit similar behaviour, consistent with enrichment by core-collapse supernovae, whereas Fe shows weaker variations, reflecting its delayed production by Type Ia supernovae. Nitrogen displays the largest phase offset (ionised-neutral), with enhancements of up to $Delta$N/H~1.5 dex and $Delta$N/O>1.5 dex in the ionised gas relative to the neutral phase, indicating localised enrichment by massive stars and inefficient mixing between gas phases on Myr timescales. While the ionised gas exhibits signatures of feedback-regulated chemical enrichment and large-scale abundance gradients, corresponding trends are weak or absent in the neutral gas, consistent with metals remaining largely confined to the immediate star-forming environment during the earliest stages of cluster evolution in a massive grand-design spiral.
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All authors Adarsh Ranjan, Bethan L. James, Svea Hernandez, R. Rickards Vaught, Nimisha Kumari, Alessandra Aloisi, Peter Zeidler

High Energy Astrophysical Phenomena

Locating the missing baryons in the warm-hot intergalactic medium with fast radio bursts and the Sunyaev-Zel'dovich effect

Dao-Hong Zhai, F.Y. Wang, Zi-Gao Dai et al. (+1 more)

Traditional astronomical censuses in the late-time Universe can only account for a fraction of the baryonic matter budget. Hydrodynamical simulations predict that the missing baryons reside in the vast filamentary structures of the cosmic web as a highly diffuse, warm-hot intergalactic medium (WHIM). Observing the WHIM directly has remained a long-standing challenge due to its typical temperature. In this study, we report the first detection of spatial cross-correlations between the dispersion measures (DMs) of fast radio bursts (FRBs) from the second CHIME/FRB catalog and the thermal Sunyaev-Zel'dovich (tSZ) Compton-$y$ map from the Planck satellite. By masking virialized galaxy clusters to isolate the diffuse signal, we find a positive correlation with a probability $>99.77\%$ between FRBs and tSZ maps. Our joint parameter inference constrains the fraction of cosmic baryons in the WHIM to be $f_{\rm WHIM}=0.48$ with a $68\%$ confidence interval of $0.27<f_{\rm WHIM}<0.61$, anchored at a mean WHIM temperature of $2.4 \times 10^6\ {\rm K}$. More rigorous masking strategies confirm the signal originates from the WHIM instead of galaxy clusters. Our result demonstrates that the missing baryons are residing in the diffuse gas within the cosmic web, closing the cosmic baryon budget in the local Universe.
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All authors Dao-Hong Zhai, F.Y. Wang, Zi-Gao Dai, Renyue Cen

Sunday 9 August

Astrophysics of Galaxies

An Identifiability Audit of One-Parameter Structural Corrections to the Radial Acceleration Relation in SPARC

Lukas A. Sosna

We ask whether any one-parameter structural correction to the radial acceleration relation (RAR) can be uniquely recovered from SPARC rotation curves, and answer with an identifiability audit: each candidate is benchmarked against per-galaxy nuisance freedom, with predictive scoring against mass-only and data-quality baselines. In the full sample (N = 126) the answer is no: a hybrid compactness term improves the fit, but zero-point freedom absorbs the gain, and in cross-validation the model fails to out-predict a mass-only baseline and loses to a quality-flag baseline. One regime retains structural information: in gas-dominated, low-acceleration disks – where MOND's strict locality and $\Lambda$CDM feedback models diverge most sharply – the RAR residual correlates with compactness ($r=0.46$, $p=1.3\times10^{-4}$), remains significant under hierarchical partial pooling ($\beta=0.23$, $p=1.7\times10^{-5}$; N = 63), and survives canonical joint control for quality, sampling, mass, inclination error, and first-order pressure support ($r=0.30$, $p=0.02$). All significant results pass a Benjamini-Hochberg correction over the declared 27-test family. Three limits temper that survival: it is not significant under rank-based control over the widest proxy set; it resides in faint dwarfs independent surveys do not reach; and after mass control it is shared across the mass-size manifold. Pressure support brackets the interpretation – isotropic drift correction absorbs a quarter of the amplitude, while a Jeans treatment overcorrects resolved cases – leaving the physical origin undetermined. The audit's product is the extraction limit: claimed corrections must clear the 0.106 dex per-galaxy nuisance floor, a mass-only baseline, and data-quality stratification.
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Instrumentation and Methods for Astrophysics · Cross-listed from eess.SY

Horizon-Dependent Tube MPC for Spacecraft Rendezvous on Elliptical Orbits with Conditional Robust Constraint Satisfaction

Omer Burak Iskender

Spacecraft rendezvous on elliptical orbits must hold a safety corridor under navigation noise, unmodelled perturbations, and thrust errors driven by propellant mass uncertainty. This paper develops a tube-based model predictive controller for the Yamanaka-Ankersen linear time-varying dynamics, carrying constraint-tightening tube methods from circular to elliptical orbits. A horizon-dependent, element-wise error bound propagates the actual closed-loop matrices along the prediction window, so early prediction steps keep nearly the full corridor that a constant-width tube would surrender. A multiplicative-to-additive conversion folds mass and thrust uncertainty into the same tightening recursion, and a Perron-Frobenius spectral-radius condition supplies a computable certificate that the tightening converges, with an explicit input-to-state stability gain. In a paired Monte Carlo campaign on a Mars sample-return orbit, the tube controller cuts mean corridor violations by more than an order of magnitude against a nominal predictive baseline at comparable fuel cost. A nonlinear truth-model test with oblateness perturbations well beyond the assumed disturbance budget leaves the corridor unviolated, and when the design envelope is exceeded the tightened problem becomes infeasible and the controller reverts to a saturated linear fallback, making the loss of guarantee explicit rather than silent. The construction requires only element-wise arithmetic and an open-source quadratic-programming solver.
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Earth and Planetary Astrophysics

Atmospheric Diversity of Giant Planet Analogs from 3-5um with SPHEREx

Rocio Kiman, Brendan P. Bowler, Jerry W. Xuan et al. (+2 more)

The emergent spectra of giant planets peak at thermal infrared wavelengths (3-5um) and possess atmospheric features in this regime that trace carbon chemistry, vertical mixing, clouds, and composition. However, this spectral region is challenging to access from the ground, and with JWST generally requires an independent pointing for each target. SPHEREx is providing all-sky spectra of millions of sources from 0.75-5um, enabling both individual and population-level studies of isolated and widely bound substellar objects. In this work we present a SPHEREx spectrophotometric atlas of 94 young (<300Myr) low-gravity L and T dwarfs to study their atmospheric diversity in the relatively unexplored wavelength range from 3-5um. These include free-floating planetary-mass objects in a range of ages, masses, and temperatures regularly probed with JWST and which will be accessible with upcoming instruments such as Keck/SCALES and ELT/METIS. We compute synthetic JWST/NIRCam and MKO photometry and colors across 22 filters, and examine trends in physically-motivated sets of colors, absolute magnitudes, and spectral types. We find that the lowest-gravity objects generally have the reddest 3-5um colors and tend to be brighter than field L dwarfs for a given spectral type, extending previous patterns originally established at near-infrared wavelengths. Compared to the low-gravity sample of free-floating objects, some giant planets closely follow the low-gravity locus, while others show larger scatter and more extreme colors, pointing to differences in cloud properties, temperature, metallicity, or vertical mixing. The SPHEREx data extraction code developed in this work is made available together with the extracted spectra and synthetic photometry.
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All authors Rocio Kiman, Brendan P. Bowler, Jerry W. Xuan, Narisara Mayer, Claire Finley

Solar and Stellar Astrophysics

Gas Flows and Mass Accretion Rates in Eight Dippers: HD 142666, HD 143006, HD 145718, V935 Sco, DoAr 25, EPIC 204638512, EPIC 205151387, and EPIC 203850058

Michael L. Sitko, Ray W. Russell, Korash D. Assani et al. (+2 more)

One of the scenarios used to explain the dipper phenomenon in stars is having the innermost disk regions being close to the line of sight to the star - inclined greater than 60 degrees - regardless of the inclination of the outermost disk ("mis-aligned" or "broken" disks). If the dust and gas in these disks sample the same material, edge-on disks will be viewed through larger column densities of gas and dust than the average disk. We have examined inter-night variability of eight Kepler-discovered dipper stars using the SpeX spectrograph on NASA's Infrared Telescope facility at a spectral resolving power of R~750. The He I line at 1.083 microns exhibits a wide variety of profiles, which change from night to night. In the majority of cases, an inverse P Cygni profile, indicative of inflowing gas, is present. The line profile (and continuum flux level) often change on time scales of 1 day. The Paschen and Brackett lines also change on similar time scales. In one object, V935 Sco, Pa beta and Br gamma went from being in emission to being in absorption over the course of 5 weeks. In another, EPIC 203850058, Pa beta went from being in emission in 2017 to vanishing altogether in 2018. The accretion rates determined using Pa beta for these stars tend to be smaller than those using Br gamma, indicating that the former line is more susceptible to self-absorption than the latter, as would be expected for a highly inclined disk.
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All authors Michael L. Sitko, Ray W. Russell, Korash D. Assani, Lucia Villanueva, Jesus Hernandez

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

Production of Primordial Black Holes in the Double D3-Brane - anti-D3-Brane Inflation Model

S.-H. Henry Tye

A natural extension of the successful $D3$-${\bar D}3$-brane inflation model in string theory is one with two $D3$-${\bar D}3$-brane pairs, giving rise to a novel feature in string-theory. When the first pair annihilates, $D1$-strings and $F1$-strings are produced. Following the non-commutative geometric properties in string theory, it is shown by Myers that the presence of the $D3$-charge field strength of the remaining $D3$-${\bar D}3$-brane pair leads to the formation of dielectric $3$-branes – neutral, finite-size bound states of $3$-branes with $D1$-strings. They behave as matter with little or no pressure. Spanning a wide range of masses, they seed primordial black holes in the early universe.
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Solar and Stellar Astrophysics

Synthetic Fe XIII 1074.7 nm Observations of Torsional Alfvén Waves in Coronal Waveguides

Samuel Skirvin, Richard Morton and Thomas Schad

Torsional Alfvén waves are a promising mechanism for transporting energy through the solar atmosphere, with implications for coronal heating and solar wind acceleration. Recently, signatures of torsional Alfvén waves have been observed with the Daniel K. Inouye Solar Telescope. We aim to investigate the effects of line of sight integration and plasma conditions on the observable properties of the torsional mode. Here we present three-dimensional magnetohydrodynamic simulations of multiple coronal waveguides, driven by a combination of transverse kink and torsional wave drivers, considering two plasma regimes representative of active region (AR) and quiet Sun (QS) conditions. Synthetic observables of the Fe~xiii~1074.7~nm coronal emission line are produced using the pyCELP forward-modelling framework to enable direct comparison with spectroscopic observations. In the QS regime, red-blue Doppler asymmetries are associated with the driven torsional waves, though their observed amplitudes are substantially reduced by line-of-sight integration. In contrast, the AR regime exhibits red-blue Doppler asymmetries even in the absence of an imposed torsional driver, which may be misidentified as the $m=0$ torsional Alfvén mode. In the AR setup, the red-blue Doppler asymmetries arise from strong phase mixing, generating shear flows and localised vorticity between waveguides where emission is strongest. The differences between the two regimes are governed by the location of peak emission, which is determined by the degree of density inhomogeneity. Our results support the identification of torsional Alfvén wave signatures in the quiet Sun (a weakly inhomogeneous environment), but caution should be exercised when interpreting spectroscopic observations in strongly inhomogeneous environments such as active regions.
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Instrumentation and Methods for Astrophysics

A Hybrid R-Theta Fiber Positioning Robot Using a Piezoelectric Bender for Radial Motion

Michael Schubnell, Tim Fanning, Andrew Hope et al. (+3 more)

Future massively multiplexed spectroscopic surveys require focal planes with increasingly dense arrays of robotic fiber positioners. The DESI (Dark Energy Spectroscopic Instrument) fiber positioners, based on a two-axis Theta-Phi motorized architecture, have demonstrated excellent reliability and performance during operations and provide the benchmark for evaluating new concepts. However, proposed next-generation instruments such as Spec-S5 require a substantially smaller positioner pitch than DESI, making direct scaling of the existing design challenging. Here we describe a hybrid R-Theta fiber positioning concept in which the rotation about the central axis is provided by a DESI-like Theta motor, while the radial displacement is produced by a piezoelectric bimorph bender coupled to a lightweight carbon-fiber spine. This design builds on the heritage of the the proven central rotation mechanism while replacing the Phi arm with a compact piezoelectric actuator. We discuss the trade-offs between motorized positioners, piezoelectric slip-stick tilting spines, tubular piezo actuators, and direct piezo-bender actuation. A prototype based on a DESI positioner was fabricated and tested using a commercial bimorph bender and an 8-inch carbon-fiber extension. With closed-loop control using feedback from a fiber-view camera the fiber was brought on target after two corrections with residual stability of approximately 2 microns RMS. These results indicate that direct piezo-bender actuation is a promising approach for compact fiber positioning, provided that closed-loop operation is addressed.
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All authors Michael Schubnell, Tim Fanning, Andrew Hope, Joseph Silber, Greg Tarlé, Nicholas Wenner

High Energy Astrophysical Phenomena

Timing and statistical analysis of single-pulse search pulsar discoveries from the PALFA survey

Graham M. Doskoch, Maura A. McLaughlin, B. Allen et al. (+23 more)

Almost two decades after their discovery, pulsars discoverable only through their single, dispersed radio pulses, known as rotating radio transients (RRATS), remain a poorly-understood class of objects. Compared to the overall pulsar population, few have timing solutions, limiting our ability to understand the mechanisms underlying their sporadic emission. Here, we present a single-pulse analysis of twelve sources from the PALFA survey, consisting of eleven objects initially identified as RRATs and one candidate fast radio burst. We present timing solutions for five of the sources with detections at a sufficient number of epochs and spin periods for two more. For all sources, we use a Bayesian framework to fit distributions of single-pulse energies, finding support for log-normal energy distributions and pulse-to-pulse wait times that are consistent with Poisson processes. Finally, we provide updates on the previously-published candidate fast radio burst J0613+18, with new indications that it is in fact extragalactic.
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All authors Graham M. Doskoch, Maura A. McLaughlin, B. Allen, A. Brazier, F. Camilo, F. Cardoso, S. Chatterjee, J. M. Cordes, F. Crawford, J. S. Deneva, R. D. Ferdman, P. C. C. Freire, J. W. T. Hessels, V. M. Kaspi, J. van Leeuwen, R. S. Lynch, A. G. Lyne, B. W. Meyers, E. Parent, C. Patel, B. B. P. Perera, S. M. Ransom, P. Scholz, I. H. Stairs, B. W. Stappers, W. W. Zhu

High Energy Astrophysical Phenomena

Simulation-based inference for AGN jet population modelling: Towards more robust comparisons of black hole jet speeds

Clara Lilje, James H. Matthews and Rob Fender

We present the most complete modelling of the MOJAVE 1.5 Jansky Quarter Century active galactic nuclei (AGN) jet population, using likelihood-free simulation-based inference. Due to the complex impact of a flux-limit on observed AGN data sets, careful modelling of the parent population is required. In particular, when observing and fitting to multiple data distributions likelihoods become non-intuitive. Parameter degeneracies further complicate the problem and make it suitable for likelihood-free, simulation-based inference. This method relies on a normalising flow learning the likelihood surface or posteriors directly. We extensively validate the flow to show that previous parameter estimates for the AGN jet speed distributions underestimated parameter errors significantly and do not capture the non-gaussianity of the parameter posteriors. The new results enable a better statistical comparison to other AGN population studies, but also a more accurate comparison of supermassive black hole jets with their lower mass counterparts, X-ray binaries (XRB). We find that the AGN follow a Lorentz factor distribution of the shape $N(\Gamma) \propto \Gamma^b$ with $b= -1.32_{-0.19}^{+0.20}$. This slope is consistent with the XRB Lorentz factor distribution at $2\sigma$. Simulation-based inference as a method is generally well-suited to many astrophysical problems, and this paper shows the convenient applicability of this methodology to parent population studies of jetted AGN with multiple observables specifically.
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Instrumentation and Methods for Astrophysics

The James Webb Space Telescope Absolute Flux Calibration. VI. Near-Infrared Camera Imaging and Coronagraphy

Martha L. Boyer, Benjamin Sunnquist, Bryan Hilbert et al. (+4 more)

We present an updated flux calibration for all imaging modes of the Near-Infrared Camera on JWST that converts instrumental units to physical surface brightness units of MJy sr^-1. This calibration includes observations of 19 flux standard stars spanning 3.5 years, with a mix of A dwarfs, solar analogs, and hot stars. All 5 coronagraphic setups, all 29 filters, and both weak lenses are calibrated. This is the first on-sky calibration for the weak lenses used in Time Series observations and for secondary coronagraphic configurations (long wavelength masks paired with short wavelength filters, and vice versa). We also assess count-rate differences between subarrays and the full frame, finding differences of up to ~1%. These differences are incorporated into the calibration factors. We find that the scatter in the calibration factor is typically <2%, with about half of the filter+detector[+mask] combinations reaching <1% scatter. There are no trends with detector effects such as the count rate and well depth. Images in a handful of filters of the Large Magellanic Cloud and globular cluster 47 Tuc show that residual detector-to-detector offsets are typically small (<1%), but can be as high as 4-5%. The NIRCam detectors are found to be quite stable, with possible count-rate decreases of <0.4% per year, which is within the calibration uncertainties. These new calibration factors were incorporated into the JWST pipeline in 2026 March.
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All authors Martha L. Boyer, Benjamin Sunnquist, Bryan Hilbert, Dan Coe, Varun Bajaj, Paul Bennet, Julien Girard

Instrumentation and Methods for Astrophysics

QUIJOTE scientific results - XX. Commissioning and First Results from the Thirty and Forty Gigahertz Instrument (TFGI)

M. Fernández-Torreiro, J. A. Rubiño-Martín, R. T. Génova-Santos et al. (+16 more)

We present the commissioning and first results of the Thirty and Forty Gigahertz Instrument (TFGI), which observes the sky at 31 and 41 GHz with angular resolutions of 21' and 18' from the second QUIJOTE telescope at the Teide Observatory. Its primary goal is to conduct a deep cosmological survey in selected regions of the Northern sky with high-sensitivity polarization measurements. The commissioning phase covered Nov2021-Oct2022, during which the instrument operated with a configuration of 7 receivers, 4 at 31 GHz and 3 at 41 GHz. Over this period, approximately 1200 h of data were acquired. Of these, 380 h were dedicated to calibration sources, used to characterize the instrumental properties of TFGI, including the pointing model, beam response, gain stability, polarimetric performance, and instantaneous sensitivity. We provide a detailed characterization of these properties and describe how they are being improved for future observing runs. We use 230 h of observations from bright Galactic regions (Cygnus, W43, W44, and W47) to further validate the instrument performance. As an illustrative example, we present the intensity and polarization spectral energy distributions of W44, finding good agreement with existing measurements. From the noise map of these observations, we measure a polarization sensitivity of ~8.3 $\mu$K deg$^{-1}$ after an effective observing depth of 0.57 h deg$^{-2}$. This performance, achieved considering only 2 detectors at 31 GHz, is already comparable to that achieved by WMAP (with almost 3 times the integration time per unit area, 1.61 h deg$^{-2}$). Extrapolating these results to the full TFGI array, with up to 29 detectors, we show that the instrument is expected to reach the target sensitivity of ~ 1 $\mu$K deg$^{-1}$ at both 31 and 41 GHz over three cosmological fields covering a total area of 3600 deg$^2$ after an effective integration time of 5.7 years.
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All authors M. Fernández-Torreiro, J. A. Rubiño-Martín, R. T. Génova-Santos, G. Pascual-Cisneros, A. Fasano, F. J. Casas, R. J. Hoyland, M. W. Peel, C. H. López-Caraballo, U. Bose, R. Rebolo, K. Aryan, R. B. Barreiro, R. Cepeda-Arroita, D. Herranz, E. Martínez-González, F. Poidevin, R. Puddu, P. Vielva

Solar and Stellar Astrophysics

Sun-to-Earth Coronal Mass Ejection Simulations From a Vector Magnetogram

Yifu An, Gábor Tóth and Beatrice Popescu Braileanu

We implement a novel approach to performing Sun-to-Earth coronal mass ejection (CME) simulations and test it on three geo-effective space weather events. Using a vector magnetogram observed prior to the CME as the boundary condition, we reconstruct non-linear force free field (NLFFF) solutions in solar active regions with an established magneto-frictional method. We find a pre-eruption solar corona containing the NLFFF in the AWSoM model, which then spontaneously erupts. We apply STITCH, a photospheric driving method, when needed, to increase the strength of the CME shock. The eruptions successfully produce magnetic flux ropes (MFRs) that propagate to 1 au in the full MHD simulation. The synthetic white light images of the simulated CMEs share a striking resemblance in shape to observations. The interplanetary MFRs (IMFRs) arrive at 1 au with a 1.5- to 9-hour error. A comparison of simulated solar wind plasma with in-situ measurements shows that IMFR crossing can reproduce a southward $B_z$ and often its magnitudes, which determine the geo-effectiveness of the event.
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Astrophysics of Galaxies

Exploration of UV-bright sources in Globular cluster NGC 3201 using UVIT observations

Manasi Kulkarni, Sonika Piridi, Ranjan Kumar et al. (+1 more)

We present a comprehensive study of the ultraviolet (UV)-bright stellar population in the globular cluster NGC 3201 using the Ultraviolet Imaging Telescope (UVIT) onboard AstroSat. By combining far-UV photometry of the UVIT F148W and F169M filters with Gaia and ground-based telescope optical data, we construct UV$-$optical color-magnitude diagrams (CMDs) to identify UV-bright stellar evolutionary phases. Physical parameters of all detected sources are derived by fitting stellar atmosphere models to the observed multi-wavelength spectral energy distributions (SEDs). The effective temperatures of blue horizontal branch stars (BHBs) span the range 7250$-$11250 K. We identify two extreme horizontal-branch stars (EHBs) with effective temperatures of approximately 25,000 K and 17,000 K; one lies within the cluster core radius ($r_\mathrm{c}$=1.3$'$), while the other is located outside. We also detect two candidate “gap” objects in the transitional phase between HB stars and white dwarfs, which may represent hot blue hook (BHk) stars. For the blue straggler stars (BSSs), we determine effective temperatures, radii, and luminosities through SED fittings, and estimate their masses and isochrone-equivalent ages using PARSEC isochrones. Finally, we studied the normalized cumulative radial distribution of the observed BHB stars, BSSs, MS stars, RGB stars, and variable stars along with the specific frequency of BSSs across the cluster. These results provide new insights into the late-stage stellar evolution and dynamical processes in NGC 3201.
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All authors Manasi Kulkarni, Sonika Piridi, Ranjan Kumar, Ananta C. Pradhan

Solar and Stellar Astrophysics

Coronal Rain Driven by Low-Frequency Impulsive Heating: Dependence of Dynamics and Morphology on Coronal Heating and Magnetic Field

Takero Yoshihisa and Takaaki Yokoyama

We performed numerical simulations to investigate how coronal heating and magnetic field strength regulate the dynamics and morphology of coronal rain in the solar corona. Coronal rain is widely interpreted as a manifestation of thermal non-equilibrium and thermal instability. Many previous studies have investigated condensation under (quasi-)steady heating scenarios, but such heating models do not fully explain the observed properties, including multiple clumps and symmetric drainage toward both loop footpoints. Condensation driven by low-frequency impulsive heating has been much less explored and may produce distinct coronal rain morphology and drainage dynamics. The role of the coronal magnetic field also remains poorly understood. We conducted 1.5-dimensional magnetohydrodynamic simulations along a single strand with self-consistent coronal heating, upon which a single impulsive heating event was imposed. Two key parameters were systematically explored: the duration of localized heating and the strength of the coronal background magnetic field. We find that condensation can be triggered even by a single impulsive heating event, provided that the injected energy is about an order of magnitude larger than that in the steady heating case. Condensation becomes more likely for longer heating durations and weaker magnetic fields. The dynamics of coronal rain depend strongly on the heating duration. When the heating duration is shorter than the radiative cooling timescale, condensations drain toward both loop footpoints. We also find that weaker magnetic fields enhance the nonlinearity of Alfvén waves, promoting fragmented condensations. These results demonstrate that the heating duration and coronal magnetic field strength play key roles in regulating coronal rain formation and dynamics.
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