High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Testing f(R) gravity using gravitational-wave signals from binary mergers
M.D.C. Torri
Recently, several studies have investigated the validity of General Relativity predictions. Gravitational waves provide an ideal probe for testing the theory in the strong-field regime. In this work, we consider a class of modified-grevity theories, specifically f(R), and scrutinize their predictions for the gravitational-wave emission from the coalescence of two astrophysical compact objects. We also assess the impact of next-generation gravitational-wave detectors on the ability of test these estensions of General Relativity.
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Cosmology and Nongalactic Astrophysics
A comparative study of emergent dark energy models
Andrés García-Rivera, A. Hernández-Almada, Miguel A. García-Aspeitia et al. (+1 more)
Late (emergent) dark energy models that involve a
hyperbolic tangent in their dynamic equations have achieved success due to their simplicity, the possibility of resolving the Hubble tension, and, in some cases their consistency with the Dark Energy Spectroscopic Instrument (DESI) results. Among the most studied are the Phenomenological and General Emergent Dark Energy Models (PEDE and GEDE, respectively), the variable
curvature model, and the graduated dark energy model. Our goal is to include the
curvature term in the models and perform a robust comparative study using diverse data samples, in particular,
Cosmic Chronometers, Type Ia
supernovae,
Baryon Acoustic Oscillations from DESI-DR1, and
Cosmic Microwave Background Radiation. This study presents the Universe age, the deceleration, the $w_{eff}$ parameter reconstruction, the
redshift transition, and the best fit for the free parameters of each model. Our collected evidence from Akaike Information Criterion and
Bayesian Information Criterion indicates that the best candidate is the PEDE model. Nevertheless, the variable-
curvature model is the only model that exhibits a decelerated phase near $z=0$, consistent with the results from DESI.
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All authors Andrés García-Rivera, A. Hernández-Almada, Miguel A. García-Aspeitia, V. Motta
Earth and Planetary Astrophysics
Astro-Hunters: Machine Learning for Exoplanet Transit Detection in TESS Photometry
Fatimah Emad Eldin
Finding
planets beyond the
Solar System is now largely a data-analysis problem: photometric surveys return far more
stellar light curves than can be inspected by eye, and machine learning is increasingly asked to recognise the faint, periodic dimming of a transiting
planet. Whether such a detector works turns on a choice that is seldom reported: how its training labels were made. No catalogue disposes the individual measurements a per-cadence detector must classify, so the annotation has to be derived, and this paper asks what that costs. We present Astro-Hunters, an end-to-end pipeline over TESS two-minute photometry:
retrieval, detrending, seven sliding-window statistics per cadence, and gradient-boosted classification. These components are deliberately conventional. What is new is the treatment of label provenance as an experimental variable, a corpus of 189,279 cadences from twelve confirmed hosts annotated from published ephemerides rather than from the photometry, and a physical bound on what the task permits. Six classifier families are compared under a
star-disjoint protocol. Holding features, model and protocol fixed, precision–recall performance spans a factor of 29 across label sources against 1.8 across architectures. Labels from an isolation forest fitted to the classifier's own features give an apparent AUC of 0.9915 that measures circularity; an unconverted transit epoch drives performance to chance; correct annotation gives AUC 0.788 at 5.3 times the prevalence baseline. The ceiling is observational, not architectural: a median single-cadence signal-to-noise ratio of 2.10 caps per-cadence AUC at 0.932. A Box Least Squares baseline recovers eight of twelve orbital periods from one sector. Phase-folding, not classifier capacity, is what makes the transit signal accessible.
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Cosmology and Nongalactic Astrophysics
Investigating The Effects of Early Dark Energy on Large-scale Structure Within the EDENS Suite
Sophie Hodgson, Patrick Wells, Katrin Heitmann et al. (+1 more)
Early Dark Energy (EDE) models have been suggested as a possible solution to the so-called Hubble Tension, a discrepancy of the measurement of the Hubble constant at early and late times. In this paper, we investigate the effects of EDE on large-scale structure probes of cosmology via the EDENS (Early Dark Energy N-body Simulations) suite. The EDENS suite extends the reach of available EDE simulations considerably by adding volume and resolution. We derive several key metrics, such as the
halo mass function, the nonlinear power spectrum, and the concentration-mass relation. Furthermore, we implement a
halo occupation distribution model to populate the simulations with synthetic
galaxies. This allows us to measure the
galaxy-
galaxy correlation function and
galaxy bias. We choose an EDE model that is consistent with observations across several probes and allows for the increase of the present day value of the Hubble constant to resolve the Hubble tension. This model adds three more parameters to the standard $\Lambda$CDM model. Additionally, it requires small shifts in the best-fit $\Lambda$CDM cosmological parameters to accommodate existing observational constraints. We find significant differences between the standard $\Lambda$CDM model and the EDE model, suggesting that some of our chosen metrics may allow us to distinguish EDE from $\Lambda$CDM, and future observations should help further constrain possible cosmological models. We release outputs from our simulations via the OpenCosmo data portal.
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All authors Sophie Hodgson, Patrick Wells, Katrin Heitmann, Niyantri Krishnan
Cosmology and Nongalactic Astrophysics
Dark Energy in the $w-c_s^2$ Plane
Oem Trivedi, Robert J. Scherrer and Alfredo Gurrola
We introduce a unified framework for dark energy diagnostics based on the joint phase space of the equation of state $w$ and the sound speed $c_s^2$. The resulting $w-c_s^2$ plane provides a minimal extension beyond background cosmology, capturing both the expansion history and perturbative properties within a single representation. Building on this framework, we define the microphysical flow parameter $F=dc_s^2/dw$, which encodes the dynamical relation between background
evolution and perturbative response. We derive a direct connection between the present-day value $F_0$, $H_0$, and $\sigma_8$, and show that the microphysical flow parameter enables a hierarchy of increasingly stringent consistency tests that substantially reduce the viable dark energy theory space. We further demonstrate how trajectories in the $w-c_s^2$ plane distinguish models that are nearly degenerate at the level of $w(a)$, including canonical quintessence, Chaplygin gas models, and noncanonical scalar field realizations. This framework provides a compact phenomenological bridge between dark energy microphysics and future perturbation-sensitive observations, establishing $F_0$ as a useful discriminator of the kinetic structure underlying
cosmic acceleration.
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Earth and Planetary Astrophysics
Atmospheric Reconnaissance of TRAPPIST-1 f with JWST NIRISS SOSS: No Evidence for the Transit Light Source Effect
Olivia Lim, René Doyon, Ryan J. MacDonald et al. (+25 more)
In just over three years of operation, JWST has observed all seven
planets of the TRAPPIST-1 system. The two innermost
planets were found to have little to no atmosphere, barring the presence of high-altitude aerosols. Here we present the first JWST transit spectra of the habitable-zone
exoplanet TRAPPIST-1 f, which were obtained with NIRISS SOSS over the course of five transits. At least one
stellar flare occurred in each visit, but unlike observations of closer-in TRAPPIST-1
planets, no evidence for contamination of the transit spectra from unocculted
stellar surface heterogeneities was found. This non-detection does not guarantee the absence of unocculted heterogeneities in all future transit observations of this
planet, and it could be explained by the transit chord of TRAPPIST-1 f having properties similar to the average, out-of-transit, visible
stellar hemisphere at the time of observation. The transit spectra exhibit slopes ranging from -365 ppm/um down to 15 ppm/um, which we attribute to
stellar variability, that is,
flares and/or smaller-scale events. The visits least affected by
flares rule out H2/He-dominated atmospheres with surface pressures higher than about 20 mbar at 95% confidence. For high-mean-molecular-mass atmospheres, the exact upper limits on surface pressures depend on the reduction pipeline and on the treatment of the residual slopes in the transit spectra.
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All authors Olivia Lim, René Doyon, Ryan J. MacDonald, Étienne Artigau, Michael Radica, Mykhaylo Plotnykov, Alexandrine L'Heureux, Caroline Piaulet-Ghorayeb, Louis-Philippe Coulombe, David Lafrenière, Thomas J. Fauchez, Martin Turbet, Diana Valencia, Loïc Albert, Laura Flagg, Björn Benneke, Neil J. Cook, Pierre-Alexis Roy, Lisa Kaltenegger, Charles Cadieux, Nicolas B. Cowan, Michaël Gillon, Romain Allart, Lisa Dang, Doug Johnstone, Stefan Pelletier, Jared Splinter, Jake Taylor
Instrumentation and Methods for Astrophysics
On-sky demonstration of dual-field interferometry at the CHARA Array
Narsireddy Anugu, John D. Monnier, Douglas R. Gies et al. (+10 more)
Dual-field interferometry uses a bright reference
star for real-time fringe tracking, allowing a second beam combiner to record long coherent integrations on a fainter off-axis science target. At the Center for High Angular Resolution Astronomy (CHARA) Array, we implement this mode using the six-
telescope MIRC-X and MYSTIC beam combiners in the H and K bands, respectively. We first demonstrated this capability in summer 2025 on the hierarchical triple $\alpha$~Piscium. MIRC-X tracked component A in the $H$ band, while MYSTIC observed component B in the K band, resolving the 7~mas Ba–Bb subsystem and measuring the relative astrometry of the 1.85~arcsec A–B pair with an uncertainty of 234~$\mu$as. Here, we describe subsequent phase-tracking testing, preliminary sensitivity simulations, and planned instrumental upgrades aimed at extending this mode to faint off-axis science targets.
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All authors Narsireddy Anugu, John D. Monnier, Douglas R. Gies, Jeremy Jones, Robert Klement, Stefan Kraus, Rainer Köhler, Karolina Kubiak, Cyprien Lanthermann, Edgar R. Ligon, Denis Mourard, Gail H. Schaefer, Nicholas J. Scott
Instrumentation and Methods for Astrophysics
The Roman Coronagraph Community Participation Program: target database and tools
Dmitry Savransky, Rifah Tasnim, Saanika Choudhary et al. (+13 more)
The Nancy Grace Roman Space
Telescope, set to launch in Fall 2026, will carry the Coronagraph Instrument, which will, for the first time, demonstrate high-contrast imaging with active wavefront control in visible wavelengths from space. In preparation for execution of the Coronagraph's commissioning and observing programs, the Roman Coronagraph Community Participation Program (CPP) has developed a target database and associated ecosystem of publicly accessible tools for observation planning and scheduling. The target database includes both
stars and known sub-
stellar companions and disks that may be observed by the Coronagraph instrument during its primary mission. Targets in the database include
planet and disk hosts as well as calibration
stars, reference
stars, and engineering program targets. The database is designed to operate in conjunction with a variety of tools, including an exposure time calculator, a pointing and keepout calculator, and a reference
star selection tool. Here, we describe the current schema and contents of the database and demonstrate how it and its associated tools are being used for observation planning.
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All authors Dmitry Savransky, Rifah Tasnim, Saanika Choudhary, Hovik Grigoryan, Justin Hom, Bijan Nemati, Neil Zimmerman, Ramya Anche, Nicholas Phillips, Louie Donesa, Parth Mittal, Amira Razack, Savaas Iqbal, Javier Majumdar, Schuyler G. Wolff, Vanessa P. Bailey
Instrumentation and Methods for Astrophysics
The Roman Coronagraph Community Participation Program: Observation planning and data reduction for polarimetric mode
Ramya M Anche, Toshiyuki Mizuki, Justin Hom et al. (+25 more)
Reflected-light polarimetry of
exoplanets constrains and resolves degeneracies in atmospheric properties, while polarized light observations of debris disks enable the characterization of
dust-grain properties. The best-effort polarimetric mode of the Roman Coronagraph Instrument will be able to perform multi-wavelength observations of planetary systems using both the Hybrid Lyot Coronagraph (HLC) and the Shaped Pupil Coronagraph (SPC). This paper presents an overview of observation planning, simulations, and data reduction procedures for the polarimetric mode of the Roman Coronagraph. As an initial test of simulation and data reduction, a
dataset of polarimetric observing sequences for the debris disk HD 172555 in HLC mode was generated using corgisim with estimated observation parameters, and data reduction was performed using corgidrp, incorporating all relevant noise factors and calibration products. Currently, mock calibration products are used in corgidrp; these will be replaced with simulated calibration products in future updates
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All authors Ramya M Anche, Toshiyuki Mizuki, Justin Hom, Alexis Lau, Saanika Choudhary, Jaren N. Ashcraft, Clarissa Do O, Tsutsumi Nagai, Sophie Noiret, Eric Shen, Taichi Uyama, Chen Xie, Jingwen Zhang, Vanessa P. Bailey, Eric Cady, Jessica Gersh-Range, Julien H. Girard, Guillermo Gonzalez, John Livingston, Bertrand Mennesson, Maxwell A. Millar-Blanchaer, Julia Milton, Naoshi Murakami, Dmitry Savransky, Motohide Tamura, Jason J. Wang, Schuyler G. Wolff, Marie Ygouf
Cosmology and Nongalactic Astrophysics
Confirmation of the Finch Flatter-Fainter Relation for the Quadruple Images of Lensed Point Sources
Kaitlyn E. Roman and Paul L. Schechter
Finch et al (2002) derived relations for the summed absolute magnifications of quadruply lensed images that vary inversely with flattening in two alternative isothermal gravitational potential models. However, they did not elaborate on the selection effects this "flatter-fainter” relation induces in actual lensed systems. We test the relation against the Luhtaru et al (2021) sample of 39 quadruply lensed
quasars (38 of which we model successfully), using predicted rather than observed magnifications to avoid the complication of microlensing. We found that the summed predicted magnification decreases by a factor of ten over the observed range of flattening.
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Astrophysics of Galaxies · Cross-listed from gr-qc
Exact black hole solutions with semi-symmetric vectorial torsion
Lehel Csillag and Tiberiu Harko
Semi-Symmetric metric
gravity extends general relativity by introducing a semi-symmetric connection with vectorial torsion. The modified field equations contain extra contributions from the torsion vector and its derivatives. Assuming a purely radial torsion vector consistent with spherical
symmetry, we derive two exact
vacuum solutions. The metric depends on two integration constants, defining the Schwarzschild radius and a new cosmological-type length scale. Classical
Solar System tests, including perihelion precession, light deflection, and radar echo delay, are used to constrain the new length scale and the associated deviations from general relativity. The thermodynamic properties of the resulting black hole solutions are investigated, and it is shown that the vector perturbation sector is linearly stable.
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Instrumentation and Methods for Astrophysics
Simulating Zernike-based CWFSing with HCIPy
Klaus Subbotina Stephenson and Kate Jackson
This work explores optimal sensing distances in Zernike-based
Curvature WaveFront Sensing (CWFS). By using HCIPy, an open-source Python package, we simulate the first 100 Zernike modes at a variety of propagation distances (1 to 20,000 m) to explore the relationship between the propagation of a wavefront and its spatial complexity to understand an idealized CWFS' sensitivity to individual modes. We find that there exist distinct optimal sensing distances for low-spatial-order-modes, with high-spatial-order modes demonstrating grouping behavior at exponentially shorter optimal sensing distances. Our results indicate that there is a sensitivity gap in current CWFSing that can be resolved by resorting to a high number of sensing planes for the low spatial order regime, with one sensing plane for each individual low-order mode; similarly, we propose several high-order regime sensing planes, with each sensing plane dedicated to small groups of localized modes centered around the highest modal sensitivity at a given propagation distance. We also discuss the caveats in dealing with high-order Zernike modes and the need for carrying out further propagation analysis in the
Fourier space to extend preliminary work presented here. Lastly, we suggest the development of a new reconstruction
algorithm that weighs the ability to reconstruct a complete wavefront according to the sensitivity (gain) to each mode at an individual sensing distance.
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Cosmology and Nongalactic Astrophysics
Kazuyuki Akitsu, Shi-Fan Chen and Zvonimir Vlah
Galaxy shapes are unique tensor tracers of large-scale structure, providing a promising avenue to both enhance current cosmological programs and detect new physics beyond the scalar sector. We develop a general formalism to describe the full 3D structure of
galaxy shapes and their statistics, including the breaking of isotropy by the line of sight and
redshift space distortions. We constructively show that the
redshift-space mapping generates a kinematic basis whose form factors are strictly
polynomial in the line-of-sight angle $\mu = \hat{k} \cdot \hat{n}$, and that parity selection rules restrict scalar-tensor and tensor-tensor correlators to 3 and 13 independent form factors, respectively, with the latter further reduced to 9 by exchange
symmetry. We show that this polynomiality is preserved transforming into a total helicity basis denoted by total angular momentum $M$—sourced to be nonzero by powers of the line-of-sight $\hat{n}$—and that this is equivalent to the form factors having
spin weights $(1 - \mu^2)^{|M|/2}$ and described by associated Legendre
polynomials $P^{|M|}_\ell$. We construct
estimators for form factors in the normalized total-helicity basis that provide the optimal angular weighting to extract shape information, and connect the full tensor basis to projected shape statistics. To validate our formalism, we study the above tensor form factors within a toy model, showing that all allowed channels are generated even within simplified assumptions, and apply our
estimators to
halo shape statistics in N-body simulations wherein all channels up to total angular momentum $|M| \leq 2$ are detected. We anticipate that the methods developed here will have applications ranging from optimal extraction of intrinsic-
alignments in hydrodynamical simulations to identifying new physics in tensor channels forbidden by selection rules in the standard model of cosmology.
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Instrumentation and Methods for Astrophysics
The Roman Coronagraph Community Participation Program: trials and triumphs of designing an observing program for a technology demonstration instrument
Schuyler G. Wolff, Vanessa P. Bailey, Justin Hom et al. (+19 more)
The Coronagraph Instrument onboard the Nancy Grace Roman Space
Telescope serves as a crucial technology pathfinder for the Habitable Worlds Observatory, with on-sky verification of high-contrast imaging techniques and the potential to image a Jupiter analog in reflected light for the first time. Together with the Roman Project Team, the Community Participation Program (CPP) is responsible for target selection, preparatory observations, developing an exposure time calculator, target database, data reduction pipeline, simulation tools, and engagement with the broader community. Here we present an overview of the CPP activities over the past two years with an emphasis on observation planning activities for the initial in-orbit checkout and the first six months of the observation phase. Finally, we present future opportunities for the astronomical community to interact with the data as it becomes public early in the mission.
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All authors Schuyler G. Wolff, Vanessa P. Bailey, Justin Hom, Beth Biller, Dmitry Savransky, Julien H. Girard, Ellis Bogat, Óscar Carrión-González, Clarissa R. Do Ó, Masayuki Kuzuhara, Chen Xie, Maxwell Millar-Blanchaer, Susan Redmond, Johan Mazoyer, Macarena Vega-Pallauta, Gael Chauvin, Matthieu Ravet, Alexandra Greenbaum, Eric Cady, Ramya Anche, James Ingalls, the Roman Coronagraph Community Participation Program Team
Instrumentation and Methods for Astrophysics
The Roman Coronagraph Community Participation Program: pre-launch reference star list and impact of reference star properties on post-processing performance
Justin Hom, Schuyler G. Wolff, Jessica Gersh-Range et al. (+51 more)
The upcoming Roman Coronagraph will be the first high-contrast instrument in space capable of high-order wavefront sensing and control technologies, a critical technology demonstration for the proposed Habitable Worlds Observatory (HWO) that aims to directly image and characterize habitable exoEarths. The nominal Roman Coronagraph observing plan involves alternating observations of a science target and a bright, nearby reference
star for both wavefront calibration and reference differential imaging post-processing. Reference
star criteria for the most demanding coronagraph mode are restrictive, limiting the sample to only 40 candidates for which thorough observational vetting is needed to assess their suitability. Reference
star properties such as resolved diameters, presence of circumstellar
dust, and close point sources may also have more subtle impacts on post-processing efficacy that may inhibit final contrast performance. In this work, we describe the current progress of the CoronaGraph Instrument Reference
stars for
Exoplanets (CorGI-REx) observing campaign, a 300+-hour observing campaign that utilizes instruments from around the world to vet reference
stars for high-order wavefront control suitability. We will present the pre-launch list of reference
star candidates being utilized for the Roman Coronagraph Observation Phase constructed from a thorough analysis of high contrast and interferometric observations. We will also present the results of simulations investigating the impact of reference
star resolved diameters and companions on post-processing performance. We conclude by discussing the importance of reference
star selection for scheduling observations and optimizing contrast performance for the Roman Coronagraph along with implications for HWO coronagraph operations.
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All authors Justin Hom, Schuyler G. Wolff, Jessica Gersh-Range, Ramya M. Anche, Vanessa P. Bailey, Jean-Philippe Berger, Beth A. Biller, Wolfgang Brandner, Marah Brinjikji, Gaël Chauvin, David R. Ciardi, Catherine A. Clark, Laird M. Close, Robert J. De Rosa, Sarah Deveny, Warren B. Foster, Julien H. Girard, Alexandra Z. Greenbaum, Olivier Guyon, Sebastiaan Y. Haffert, Alexander D. Hedglen, Steve B. Howell, Parker T. Johnson, Maggie Y. Kautz, Jay K. Kueny, Masayuki Kuzuhara, Manon Lallement, Rico Landman, Colin Littlefield, Jean-Baptiste Le Bouquin, Jialin Li, Joshua Liberman, Joseph D. Long, Miles Lucas, Jennifer Lumbres, Bruce Macintosh, Jared R. Males, Eric Mamajek, Matthijs Mars, Eden A. McEwen, Avalon L. McLeod, Maxwell A. Millar-Blanchaer, Toshiyuki Mizuki, Sophie Noiret, Tiffany Nguyen, Lauren Schatz, Nicholas T. Schragal, Adam K. Taras, Elena Tonucci, Katie Twitchell, Kyle Van Gorkom, Macarena C. Vega-Pallauta, Jason J. Wang, Jingwen Zhang
Instrumentation and Methods for Astrophysics
pynucastro 3: A community library for nuclear astrophysics
Zhi Chen, Khanak Bhargava, Eric T. Johnson et al. (+8 more)
We describe the latest release of pynucastro: a community python library for
nuclear astrophysics. The goal of the pynucastro project is to build the tools needed to interactively explore
nuclear properties, reaction rates, and networks, and to export these networks to a variety of simulation codes. Major changes in pynucastro since the last major release include new rate approximations, a
stellar equation of state, support for the StarLib library and rate uncertainties, and new tools for exploring networks.
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All authors Zhi Chen, Khanak Bhargava, Eric T. Johnson, Reth Lopes, Melissa Rasmussen, Alexander Smith Clark, Michael Zingale, Brendan Boyd, Kiran Eiden, Sam Glosser, Don E. Willcox
Instrumentation and Methods for Astrophysics
The Roman Coronagraph Community Participation Program: data reduction pipeline design and implementation
Jason J. Wang, Maxwell A. Millar-Blanchaer, Marie Ygouf et al. (+39 more)
The Roman Space
Telescope Coronagraph Instrument will demonstrate a series of technologies and techniques to enable the direct detection of reflected-light
planets with space-based observatories. To characterize and validate the performance of the Coronagraph Instrument, the Community Participation Program is developing corgidrp, an open-source Python-based data reduction pipeline. The pipeline can process data from the required and best-effort observing modes and their associated calibration sequences into calibrated science-ready data products. We present the software design and implementation of corgidrp and the motivation behind specific design decisions. We describe the software architecture, data flow, processing steps, automation tools, testing framework, and development philosophy. We also outline future development plans in preparation for on-sky data.
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All authors Jason J. Wang, Maxwell A. Millar-Blanchaer, Marie Ygouf, Julia Milton, Jürgen Schreiber, Kevin J. Ludwick, Ellis Bogat, Amanda Chavez, Eric Shen, Aneesh Baburaj, Ramya Anche, Toshiyuki Mizuki, Taichi Uyama, Ezar Shinbaro, Alexis Lau, Neil T. Zimmerman, Sophie Noiret, William Balmer, Ben J. Sutlieff, Adrien Maillard, Matthias Samland, A J Eldorado Riggs, Clarissa Do Ó, Jingwen Zhang, Giovanni M. Strampelli, Lisa Altinier, Michael Liang, Jessica Gersh-Range, Kylee Fluckiger, John Livingston, Malachi Noel, Dmitry Savransky, Michele Woodland, Tsutsumi Nagai, Justin Hom, Al Niessner, Cynthia Wong, Eric J. Cady, Vanessa P. Bailey, Guillermo Gonzalez, Alexandra Z. Greenbaum, Enrico Biancalani
High Energy Astrophysical Phenomena
The X-Ray Continuum Emission Region in the Lensed Quasar SDSS J133907.23+131038.6 is Much Smaller than the Accretion Disk
Christopher W. Morgan, James B. Margeson, Gilberto Garcia et al. (+4 more)
We analyze microlensing variability in 15 seasons of optical monitoring data and 4 epochs of new X-ray observations of the doubly-imaged gravitationally lensed
quasar SDSS J133907.23+131038.6 to place empirical constraints on the size and structure of that system's X-ray and optical continuum emission regions. Employing a
Bayesian Monte Carlo method, we analyzed ground-based optical light curves to constrain the half-light radius of the far-UV source $\log(r_{\rm 1/2, FUV}/{\rm cm})=15.78^{+0.26}_{-0.28}$ at 193 nm, the rest-frame center of the r-band, assuming a $60^\circ$ inclination angle. This size corresponds to $\sim100\,{\it r}_{\rm g}$ for a $4.0 \times 10^{8} \: {\rm M_{\odot}}$ black hole. We measured the half-light radius of the full band ($0.2-8.0 \: {\rm keV}$) X-ray continuum emission region $\log(r_{\rm 1/2, X_{full}}/{\rm cm})=14.32^{+0.23}_{-0.31}$, a size measurement that is consistent with the radius of the innermost stable circular orbit (ISCO) in the Schwarzschild metric.Two shifted Fe K$\alpha$ lines caused by microlensing are detected in the stacked spectrum of image A at 5.9 and 8.9~keV at $>99\%$ significance.
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All authors Christopher W. Morgan, James B. Margeson, Gilberto Garcia, Xinyu Dai, Luis J. Goicoechea, Vyacheslav N. Shalyapin, George Chartas
Solar and Stellar Astrophysics
Tracking nonlinear solar-wind dynamics over three solar cycles using Wind observations
Dario Javier Zamora and Facundo Maximo Abaca
The
solar wind is a turbulent, weakly collisional
plasma characterized by non-Gaussian fluctuations, long-range correlations, and multifractal dynamics. We investigate the long-term
evolution of these properties using hourly
proton density measurements obtained directly by the Wind spacecraft over 1995–2025. The use of a single-spacecraft
dataset provides an independent test of previous results derived from the multi-spacecraft OMNI database. The three components of the nonextensive $q$-triplet are estimated within one-year sliding windows shifted monthly: $q_{stat}$ from the distribution of density increments, $q_{rel}$ from the decay of the autocorrelation function, and $q_{sens}$ from the multifractal spectrum. Their mean values, $q_{stat}=1.71\pm0.07$, $q_{rel}=4.62\pm0.52$, and $q_{sens}=-0.45\pm0.27$, confirm the persistent presence of heavy-tailed statistics, slow relaxation, and weakly chaotic multifractal dynamics. The parameters nevertheless exhibit distinct temporal variability and relationships with
solar activity. The
Fourier spectrum of $q_{stat}$ contains a dominant period of approximately $10.1$ years, while its correlation with the sunspot number is positive and moderate ($r=0.611$). Correlation and mutual-information analyses show that $q_{stat}$ is primarily associated with
solar proxies, whereas $q_{sens}$ displays stronger relationships with geomagnetic indices and $q_{rel}$ exhibits weaker dependencies. An anomalous enhancement of $q_{stat}$ around 2004 coincides with a sequence of intense interplanetary disturbances, although possible effects related to Wind's orbital transition must also be considered. These findings demonstrate the robustness of the nonextensive description and show that the statistical and dynamical properties of
solar wind
proton density show evidence of modulation by
solar activity.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.comp-ph
Validating direct solvers for Newton's gravitational N-body problem, and the systematic comparison between IEEE floating point and Posits
Simon Portegies Zwart
We present a systematic comparison between arbitrary precise arithmetic and integration, IEEE-754 compliant floating point arithmetic (fp16, bfp16, fp32, double precision fp64, and quadruple precision fp128), and two implementations of Posits (type III unum) for solving Newton's chaotic N-body problem. Each implementation is benchmarked with arbitrary precise calculations to objectively evaluate their performance in precision as well as speed. We rely on hardware and compiler implementations for fp64, and software implementations for arbitrary-precision arithmetic and Posits. Half precision arithmetic (fp16, bfp16, and Posits$<16,1>$) are insufficiently precise for solving Newton's equations of motion. Single precision (fp32, and Posits$<32,2>$) could be used for statistical ensemble calculations, but lead to relatively large errors in any individual strong encounter. All 64-bit implementations fp64 as well as Posits (Posits$<64,3>$) experience difficulty in our tests. One of the implementations of Posits (Universal) gives precision comparable to fp64 but is slow (by at least an orders of magnitude compared to fp64 after correcting for the more efficient hardware support for the latter). The other (CPPPosits) has a speed comparable to fp64 but has systematically larger errors (by about an order of magnitude compared to fp64 with excesses exceeding two orders of magnitude). As a consequence, this implementation leads to a systematic drift in the result space and has difficulty resolving close encounters. Posits and fp64 have difficulty when integrating a dynamical system in a moving reference frame; testing Galileo invariancy. In their current implementation, Posits do not seem to be the ideal alternative for fp64 when integrating chaotic or stiff ordinary differential equations, such as Newton's equations of motion.
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Earth and Planetary Astrophysics
Understanding the Energy Input Required for Methane Emission on CWISEP J193518.59-154620.3: A Comprehensive Analysis
Kayla J. Smith, Mark S. Marley, Tommi T. Koskinen et al. (+1 more)
The Y
dwarf WISE 1935 exhibits a thermal inversion in its radiative atmosphere, producing methane emission features in its JWST spectrum, but the physical mechanism responsible for this inversion remains unknown. Using the open-source radiative–convective
equilibrium code PICASO, we model atmospheric heating with Chapman energy deposition profiles to reproduce the observed thermal inversion and methane emission feature. Our models require heating rates of approximately 10^5-10^6 erg cm^-2 s^-1. We show that the atmospheric response depends primarily on the integrated heating deposited in the observable atmosphere, revealing a degeneracy between heating magnitude, vertical extent, and emitting surface fraction. Disequilibrium chemistry lowers the required energy input by lowering CH$_4$ opacity and strengthening the inversion. Comparison with recent electron-beam heating models indicates that reproducing the thermal inversion in W1935 requires substantially greater energy deposition than currently predicted for brown
dwarf auroral heating, while the observed methane emission favors energy deposition near 10^-3-10^-2 bar. Our models also predict a prominent methane emission feature near 7.8 microns, along with energy-sensitive ammonia features near 6 microns, implying a bolometric luminosity greater than that yet measured. Finally, we investigate potential sources of the inferred upper-atmospheric heating. We find that Joule heating would require a strong
magnetic field and large electron densities, the latter supported by external ionization from an unidentified source. We also consider cometary impacts as a possible source of atmospheric heating.
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All authors Kayla J. Smith, Mark S. Marley, Tommi T. Koskinen, James Mang
Astrophysics of Galaxies
Measuring Simulated Circumgalactic Medium Turbulence with Emission-Weighted Projected Velocity Structure Functions in FOGGIE
Helena Bouchereau, Cassandra Lochhaas, Jake S. Bennett et al. (+1 more)
The spatially-resolved kinematics of line emission from the circumgalactic medium (CGM) of a
galaxy can contain information about the CGM
turbulence, which may play an important role in
galaxy evolution. Due to the region's diffuse nature, there have been limited observations of low-
redshift CGM emission until recent efforts that use spatially-resolved emission line kinematics to probe CGM
turbulence. We use velocity structure functions (VSFs) as a measure for the properties of
turbulence using the high-resolution cosmological zoom-in FOGGIE simulations. We focus on the location of the "turnover" in the VSF slope, often used as a measurement of the
turbulence driving scale, and study how resolution, measurement area size, projection effects, and gas temperature influence the inferred CGM
turbulence driving scale. We find that projection significantly lowers the VSF normalization but we do not find significant differences in the slope between 3D VSFs and emission-weighted projected 2D VSFs. We find that the size of the area used to measure the VSF, which can be thought of as the size of the emission nebula for a given instrument sensitivity, correlates directly with the turnover location in the VSF. These dependencies should be considered when using VSFs to interpret CGM
turbulence from emission data, as projection, resolution and sensitivity constraints, and the temperature of the gas probed will all have a measurable effect on the VSF structure and the corresponding inferred turbulent properties.
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All authors Helena Bouchereau, Cassandra Lochhaas, Jake S. Bennett, Mandy C. Chen
Astrophysics of Galaxies
The VariableTNG project: Unveiling the physical drivers of galaxy quenching
Ignacio G. Alfaro, Antonio D. Montero-Dorta, Hong Guo et al. (+4 more)
Understanding the physical processes that regulate
galaxy quenching is a key challenge in
galaxy formation and
evolution. The VariableTNG (VTNG) project provides a laboratory to investigate these processes, as it systematically varies eight parameters of
galaxy formation while keeping the initial conditions fixed, allowing the effects of individual feedback prescriptions to be isolated. We use interpretable machine-learning techniques as a tool to identify the parameters that most strongly regulate the quenched
galaxy fraction. Our goal is to quantify the relative importance of the
galaxy formation and feedback parameters that regulate the quenched
galaxy fraction at z=0, determine how their influence changes across
stellar mass and environment. We compute the quenched
galaxy fraction for 26 VTNG boxes as a function of
stellar mass, black hole mass, and gas mass, considering both the total
galaxy population and separate samples of central and satellite
galaxies. We train Random Forest regressors to predict the variation of the quenched fraction relative to the TNG100-1 model and use SHAP values to quantify both the magnitude and direction of the influence of each parameter. Our analysis reveals that only a small subset of the VTNG parameters dominates the variance of the quenched fraction. The
stellar feedback wind parameter is the primary driver at low
stellar masses, while its importance gradually shifts toward AGN-related parameters at higher masses. The
supernova temperature also plays an important role at both extremes of the
stellar-mass range. This transition persists when the
galaxy population is divided into central and satellite systems. Comparisons with observational measurements further suggest that variations in these feedback parameters may contribute to the discrepancies between the fiducial TNG100-1 model and the observed passive
galaxy population.
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All authors Ignacio G. Alfaro, Antonio D. Montero-Dorta, Hong Guo, Catalina Riveros-Jara, Kexin Liu, Yikai Liu, Luis C. Ho
Instrumentation and Methods for Astrophysics
A novel technique for reflection coefficient measurement in precision cosmology
Adarsh Kumar Dash, Yash Agrawal, Somashekar R. et al. (+7 more)
The detection of the global 21-cm signal from the
Cosmic Dawn and Epoch of Reionisation remains a challenge to experiments worldwide. Emitted at a rest-frame frequency of 1420.405~MHz, this signal from the early Universe is redshifted to 40-200~MHz with a maximum brightness temperature of a few 100~mK. Efforts to detect this sky-averaged signal include experiments such as the Shaped
Antenna measurement of the background
RAdio Spectrum (SARAS) and Probing ReionizATion of the Universe using Signal from Hydrogen (PRATUSH). Detecting this faint signal requires precise calibration of the
antenna, which includes a high-precision measurement of its reflection coefficient. This measurement must be performed in situ at the observation site, as the
antenna characteristics vary significantly with the environment. PRATUSH, a space-based radiometer, faces the additional challenge of structural distortions induced by thermal cycling, necessitating multiple measurements of the reflection coefficient. This work highlights the development of an in situ Vector Network Analyser, which utilises a novel noise source-based calibration scheme and a cross-correlation spectrometer to perform magnitude and phase measurements of the complex reflection coefficient of the
antenna. Further, we demonstrate the performance of the designed network analyser using independent measurements from a precision network analyser and reflection coefficient modelling of the device under test. We find the level of non-smooth calibration systematics, which need critical control for 21-cm signal detection, to be about $10^{-5}$. Finally, we study the impact of reflection coefficient correction on sky measurements, highlighting its usability for precision 21-cm observations.
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All authors Adarsh Kumar Dash, Yash Agrawal, Somashekar R., Jayadev Ashok T., Keerthipriya S., Vishwapriya Gautam, Saurabh Singh, Mayuri Sathyanarayana Rao, Girish B. S., Srivani K.S
Earth and Planetary Astrophysics
SCExAO/CHARIS High-Contrast Pre-Launch Vetting of Roman Coronagraph Technology Demonstration PSF Reference Stars
Thayne Currie, Jie Li, Mona El Morsy et al. (+9 more)
We present deep, SCExAO/CHARIS high-contrast integral field spectroscopy and archival imaging of four candidate Roman Coronagraph PSF reference
stars within/near the Roman Continuous Viewing Zone and potentially suitable for the Coronagraph's key technology demonstration targets HIP 71618 and HIP 54515. For CHARIS data, we achieve 5-$\sigma$ contrasts down to $\sim$1.4$\times$10$^{-5}$, $\sim$6$\times$10$^{-6}$, and 10$^{-6}$ to 4$\times$10$^{-7}$ at 0\farcs{}16, 0\farcs{}25, and 0\farcs{}5 to 1\arcsec{}. Companion mass limits rule out brown
dwarfs at $\rho$ $\sim$ 0\farcs{}15–0\farcs{}25 and massive
planets at wider separations around all targets. More critically, for three of the four references our analysis disfavors companions with $V$ band contrasts brighter than 10$^{-8}$, 10$^{-9}$, and $10^{-10}$ at 0\farcs{}15, 0\farcs{}3, and 1$\arcsec{}$. Unless these targets have faint substellar companions within $\rho$ $\sim$ 0\farcs{}15, they likely lack background
stars or companions that could corrupt the Roman Coronagraph's dark hole digging to preclude detecting reflected-light
planets. For $\alpha$ Cep, our limits are a factor of $\sim$10 worse but still meet the TTR5 limit of 10$^{-7}$ beyond $\rho$ $\sim$ 0\farcs{}25: beyond 0\farcs{}4, they exclude a Jupiter-twin reflected-light companion (10$^{-9}$). Archival Keck/NIRC2 data likewise find no substellar companions with $\Delta$V $>$ 10$^{-8}$ at wider separations. Finally, we assess the observability of HIP 71618 and HIP 54515 – updated for Roman's launch date of August 30, 2026. Adding $\gamma$ Boo – not currently in the Roman CPP team reference-
star list – would improve schedulability for the tech demo's key targets.
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All authors Thayne Currie, Jie Li, Mona El Morsy, Olivier Guyon, Julien Lozi, Erica Dykes, Danielle Bovie, Sebastien Vievard, Garima Singh, Kyohoon Ahn, Vincent Deo, Yoshito Ono
Earth and Planetary Astrophysics
A Statistical Mechanics Model for Stable Rings Outside the Roche Limit
Jack T. Dinsmore
Stellar occultations have revealed two rings around the
dwarf planet Quaoar outside the Roche limit. Simulations suggest that the rings are sustained by large velocity dispersions. We present the first analytical, first-principles theory that extends the Roche limit to describe planetary rings with large velocity dispersion. The underlying principle is an analogy between a
liquid/gas phase transition and the moon/ring transition: just as high temperatures can boil a
liquid under pressure, high velocity dispersions can stabilize ring systems beyond the Roche limit. We employ statistical mechanics to derive a modification to the Roche limit that treats rings with nonzero velocity dispersion. We demonstrate the new model's consistency with previous simulations of Quaoar's outermost ring. We also note that dense regions of the ring experience negative pressure, which would cause them to shrink over time if the assumptions of the model continue to hold. This could help explain the rings' azimuthal asymmetry.
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High Energy Astrophysical Phenomena
Extreme-Mass-Ratio Inspirals in Gaseous Disks
Alexander J. Dittmann, Abhishek Hegade K. R. and Callum W. Fairbairn
Gravitational waves from extreme mass ratio inspirals (EMRIs) are precise probes of the environment of the supermassive black holes (SMBHs) they orbit. If an SMBH is actively accreting, the surrounding gaseous disk can impart hydrodynamic torques on and assist the formation of EMRIs within it. Such disk-EMRI interactions could leave measurable imprints on future observations by the
Laser Interferometer Space
Antenna (LISA), and potentially provide a route to constrain disk properties using gravitational wave observations. We present herein a detailed relativistic analysis of these hydrodynamic interactions using linear theory. We first derive a Lagrangian governing the
evolution of spiral density waves in the disk and use it to formulate a balance law for the transfer of angular momentum between the EMRI and disk. We then develop a stable numerical scheme which can be used to treat corotation resonances and find modal solutions in thin disks up to very large azimuthal numbers. Using this numerical scheme, we explore how SMBH
spins, EMRI semi-major axes, disk scale heights, sound speed gradients, and surface density gradients affect the interaction between
accretion disks and circular EMRIs. Our results show that relativistic effects substantially alter disk-EMRI interactions once the secondary orbit is within $\mathcal{O}(25)$ Schwarzschild radii from the SMBH. Comparing our numerical results with recent analytical models suggests that the impact of pressure gradients and softening of the gravitational potential is important for disks with finite thickness and cannot be captured by tuning the torque cutoff parameters in the analytical models. The framework provided here will help analyze the formation scenarios of EMRIs and build relativistically accurate waveform models of disk-EMRI interactions.
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Cosmology and Nongalactic Astrophysics
Spectral Fingerprints Beyond Degeneracies in Primordial Gravitational-Wave Sources
Subhasis Maiti
Stochastic gravitational-wave backgrounds from different
primordial mechanisms can exhibit identical peak frequencies and amplitudes, leaving their origin degenerate. We show that this degeneracy can be broken by the broadband spectral response of the gravitational-wave source. By comparing scalar-induced and gauge-field-induced gravitational waves with the same
primordial spectral profile and cosmological
evolution, we isolate the imprint of the tensor-source dynamics. Although both mechanisms exhibit the same infrared scaling, they develop distinct spectral shapes near the peak and different ultraviolet asymptotes. The local spectral index $n_{\rm gw}$ and its running $\alpha_{\rm gw}$ further characterize this source-dependent
evolution, providing a spectral fingerprint beyond the peak observables. These results show that broadband, multi-frequency observations can probe the production mechanism of a
primordial gravitational-wave background even when its peak frequency and amplitude are degenerate.
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Solar and Stellar Astrophysics
Sr and Ba yields of the First Generation(s) of stars: Constraints from metal-poor stars
Sarah Hughes, Anna Frebel, Xiaowei Ou et al. (+6 more)
We present our chemical abundance analysis of ten new extremely metal-poor
stars with $-4.05\leq\mbox{[Fe/H]}\leq-2.33$, based on high-resolution (R $\sim28,000$) Magellan/MIKE spectra. Eight of our
stars have low heavy-element abundances of $\mbox{[Sr/H]}<-4.5$ and $\mbox{[Ba/H]}<-4.0$, making them Small Accreted
Stellar System (SASS)
stars. Four are hyper
neutron-capture-element poor with $\mbox{[Sr/H]}<-5.0$, including
Gaia DR3 5729400267359655680, which sets a new record for the lowest detected Sr abundance of $\mbox{[Sr/H]} =-6.4$. We identify four distinct [Sr/Ba] groups within the wider SASS
star population which span a large range from $\mbox{[Sr/Ba]} =-2.0$ to +1.6, pointing to multiple types of progenitor events and different nucleosynthesis processes/sites. To explore the origins of this large [Sr/Ba] range, we adopt site-agnostic Sr yields of $\mbox{[Sr/H]}=-6$, $-5.75$, $-5.42$, and $-4.93$ for the four groups. Applying those yields suggests that the majority of SASS
stars formed from gas enriched by $\sim$1-10 progenitor events, consistent with expectations from their extremely metal-poor nature. We thus attribute the [Sr/H] abundance scatter to intrinsic variations in the Sr yield per nucleosynthesis site/event. Our proposed Sr yields for each [Sr/Ba] group and associated nucleosynthesis origin are a reasonable and representative approximation, good to within a factor of a few, and can constrain future theoretical heavy element nucleosynthesis calculations in early core-collapse
supernovae.
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All authors Sarah Hughes, Anna Frebel, Xiaowei Ou, Alexander Yelland, Felicia Xiao, Jorian Benke, Kali Kraus, Reidyn Wingate, Mohammad Mardini
High Energy Astrophysical Phenomena
Broadband emission of microquasar remnants
Leandro Abaroa, Gustavo E. Romero and Valentí Bosch-Ramon
Microquasar remnants (MQRs), the long-lived cocoons inflated by extinct microquasar jets, have recently been proposed as hidden
Galactic PeVatrons capable of producing ultra-high-energy gamma rays without an active central engine. While hadronic interactions can account for bright gamma-ray emission from nearby clouds, the direct detection of MQRs remains challenging because their intrinsic emission is expected to be extended and of low surface brightness. In this work, we explore the broadband emission of MQRs by focusing on the leptonic component confined within the cocoon and on particle interactions in the shocked shell surrounding it. We model the injection and time-dependent transport of relativistic particles, including
stochastic re-acceleration driven by internal
turbulence, treated as a second-order
Fermi process. We consider sub-Eddington and super-Eddington microquasar systems and compute the resulting non-thermal emission from
radio to gamma-ray energies, together with the thermal soft X-ray emission produced in the shocked shell. In the super-Eddington case, the intrinsic emission reaches peak values of $\nu L_\nu \sim 10^{35}-10^{36}\,{\rm erg\,s^{-1}}$, whereas sub-Eddington remnants are typically several orders of magnitude fainter. At 1.3 GHz, the modeled cocoon surface brightness is of order $\Sigma_\nu \sim 10^{-19}\,{\rm W\,m^{-2}\,Hz^{-1}\,sr^{-1}}$ for young powerful remnants and decreases rapidly as the remnant evolves. We find that the direct detectability of MQRs is therefore controlled mainly by surface brightness rather than by integrated luminosity. Powerful remnants may be detectable as extended synchrotron
radio cocoons and shell-dominated soft X-ray structures, whereas sub-Eddington remnants are expected to be much harder to identify directly. Our results suggest that MQRs may constitute a hidden population of extended
Galactic non-thermal sources.
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