Instrumentation and Methods for Astrophysics
The Via Project: Overview of the Science, Instrument, and Survey
The Via Collaboration
Via is a forthcoming all-sky spectroscopic survey that will achieve 100 m s$^{-1}$ radial velocity stability for millions of faint ($G \lesssim 21$)
stars while reaching LSST's single-visit depth ($r \approx 24$) for transient spectroscopy, opening new regimes in near-field cosmology and time-domain astrophysics. Via will deploy identical fiber-fed, multi-object spectrographs on the 6.5m MMT and Magellan/Clay
telescopes for a five-year, dual-hemisphere survey of $>2{,}000{,}000$
stars beginning in 2027 - timed to complement LSST. Each instrument has 576 robotically positioned fibers over a $1^\circ$ field of view, feeding two spectrographs: Viaspec ($R \approx 15{,}000$; 505-595 nm; 540 fibers) and Boombox ($R \approx 1{,}000$; 360-1010 nm; 36 fibers). Four key goals drive the survey: (1) a comprehensive survey of velocity perturbations in cold
stellar streams, sensitive to $M \lesssim 10^7$ subhalos below the threshold of
galaxy formation, a stringent test of the particle nature of dark matter; (2) a chemodynamical census of Milky Way satellite
galaxies to understand the formation of the faintest
galaxies; (3) the first 3D tomographic maps of cold gas in the circumgalactic medium via NaI absorption; and (4) the rapid characterization of thousands of transients to the single-epoch survey depth of LSST. Ancillary science - including the Ly$\alpha$ forest at $z \approx 3$-$4$, polluted white
dwarfs,
exoplanet host characterization, fast
radio burst host
galaxies, and extragalactic
dwarf galaxies - will leverage spare fibers in every pointing. The Via Project is a collaboration between the Center for Astrophysics $|$ Harvard & Smithsonian, Carnegie Observatories, Stanford University, and Yale University.
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Instrumentation and Methods for Astrophysics
THOR and HAMRR
Sean K. Terry and Jay Anderson
We present the Terry Hubble Observations of Roman (THOR) data reduction pipeline and Hubble Advanced Mining Routine for Roman (HAMRR). THOR is designed to reduce HST Wide-field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS) imaging data taken as part of program GO-17776: A Precursor Survey of the Roman
Galactic Bulge Time Domain Fields (Terry et al, 2024). The primary function of HAMRR is to query the THOR-derived catalog via a typical cone search
algorithm. Output products from HAMRR include calibrated photometry and astrometry for detected point sources in the HST catalog. The package supports additional output products such as cutout images, auto-generated color-magnitude diagrams, luminosity functions, and more. The HAMRR tool can be used in coordination with analyses of Roman, Rubin/LSST, and Euclid
Galactic Bulge targets in the near future.
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Cosmology and Nongalactic Astrophysics
Projecting the ultimate pulsar timing sensitivity to dark matter substructure in a stochastic gravitational wave background
Joshua W. Foster, Tanner Trickle and Fabrizio Vassallo
Pulsar timing arrays (PTAs) are sensitive to the gravitational influence of passing compact substructures, which can produce Doppler timing delays by accelerating
pulsars or the
Solar System barycenter, and Shapiro timing delays when passing near Earth–
pulsar lines of sight. Projections for the complete PTA sensitivity to compact dark matter (DM) substructures, such as
primordial black holes and
axion miniclusters, are challenging due to the variety of signal types ranging from rare, nearly static encounters, to dynamic flybys, to the
stochastic limit of many substructures. We address this challenge with a framework that combines Monte Carlo signal modeling and machine-learned surrogate likelihoods, enabling a unified likelihood-level analysis of signals previously treated only in simplified limiting regimes. We then use this framework to precisely assess the impact of a
stochastic gravitational wave background (SGWB), for which evidence was recently found, on the PTA sensitivity to compact DM substructures. The SGWB substantially weakens the sensitivity, and we find that in even the most optimistic observing scenario only a Shapiro search retains sensitivity to subdominant DM components when assuming SGWB parameters inferred from current measurements.
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Instrumentation and Methods for Astrophysics
Ultra-High-Resolution Astronomy with the Solar Gravitational Lens
Slava G. Turyshev
The
solar gravitational lens (SGL) is a target-specific observatory: the Sun supplies the wave-optical element, while spacecraft provide occultation, annular photometry, sampling, metrology, and inverse reconstruction. We develop an observability framework for non-
exoplanet SGL astronomy. Viability is set by image-plane scale, raster pitch, finite-source gain, source-to-background ratio, temporal coherence, PSF knowledge, calibration, metrology, and focal-line access. We separate the vector Poisson measurement operator from the scalar convolution used for
benchmarks. Four analytic scenes are propagated and reconstructed: a
solar analog and
magnetic white
dwarf at 10 pc, an M87*-scale millimeter ring/jet source, and a bright 0.1 AU protoplanetary subfield at 140 pc. Under stated kernel-mismatch, background, calibration-floor, support-mask, sampling, regularization, and imposed information-floor assumptions, the scalar reconstructions give SSIM values of 0.993, 0.918, 0.973, and 0.923. These metrics quantify scalar inverse conditioning, not delivered flight performance; FRC50, support-leakage, and information-floor sensitivity diagnostics expose the dependence on assumptions. Many self-luminous compact targets are not
photon-starved relative to a reflected-light exo-Earth reference, shifting the dominant requirements to ring extraction, coronal subtraction, detector dynamic range, PSF knowledge, cadence, spectroscopy, metrology, scan overhead, and access. The strongest bounded cases are white-
dwarf surface and
magnetic mapping, nearby
stellar surfaces, compact AGN/black-hole structure with long-wavelength instrumentation, velocity-resolved broad-line-region mapping, and
planet-forming subfields. The priority enabling program is SGL transfer-function characterization: measuring
solar-multipole,
plasma, extended-Sun, and instrumental response needed for scientifically interpretable imaging.
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Instrumentation and Methods for Astrophysics
Building a Roadmap for Hubble Science into the 2030s: Revealing Atmospheric Structure and Evolution in Substellar Worlds Using HST
Allison M. McCarthy, Merle A. Schrader, Johanna M. Vos et al. (+15 more)
Substellar objects occupy a unique place in our universe, bridging the gap between the smallest
stars and the largest
planets, and serving as powerful laboratories for understanding extrasolar atmospheric physics without the contaminating glare of a host
star. Previous studies into the atmospheric structure of these objects have revealed clouds, disequilibrium chemistry, thermal inversions, and auroral processes which each contribute to wavelength-dependent brightness variations. HST remains uniquely positioned to address key open questions in the field, such as resolving the vertical atmospheric structure, long term
evolution of the atmosphere, and detection of UV aurora in the upper atmosphere, primarily in conjunction with other facilities that probe wavelength regimes that cannot be reached with instruments on HST. We advocate for three large scale initiatives and argue that the study of the atmospheres of substellar worlds directly prepares the community for atmospheric characterization with the Habitable Worlds Observatory.
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All authors Allison M. McCarthy, Merle A. Schrader, Johanna M. Vos, Sven Kiefer, Cian O'Toole, Michael K. Plummer, Michael Poon, Daniella Bardalez Gagliuffi, Samuel Beiler, John E. Gizis, Melodie M. Kao, Gabriel-Dominique Marleau, Elisabeth C. Matthews, Philip S. Muirhead, Evert Nasedkin, Natalia Oliveros-Gomez, J. Sebastian Pineda, Kimberly Ward-Duong
Cosmology and Nongalactic Astrophysics
Pushing the Primordial Frontier: Exact Linear Solutions in Multifield Inflation
Javier Huenupi, Claudio Muñoz, Gonzalo A. Palma et al. (+1 more)
We present exact analytic solutions for the linear dynamics of a two-field inflationary system in which the
primordial curvature perturbation $\zeta$ is coupled to an isocurvature perturbation $\sigma$ of
entropy mass $\mu$. The solutions are valid for arbitrary values of $\mu$ and the dimensionless interaction strength $\lambda$. They therefore provide analytic control over the strong mixing regime in which $\zeta$ interacts with light isocurvature fields, commonly associated with rapid-turn inflation. As a first application, we derive the amplitude of the
primordial power spectrum in closed form, obtaining an expression that interpolates between the weakly mixed, strongly mixed, light-field, and heavy-field regimes. These results open the way to analytic studies of multifield observables beyond the power spectrum, including non-Gaussianity, particle production, and loop corrections.
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All authors Javier Huenupi, Claudio Muñoz, Gonzalo A. Palma, Spyros Sypsas
Astrophysics of Galaxies
PAHSPECS: Spatially Resolved PAH Spectroscopy at cosmic noon with JWST MIRI MRS
Fergus R. Donnan, Karin Sandstrom, Irene Shivaei et al. (+10 more)
We present spatially resolved spectroscopy with JWST/MIRI MRS of a representative sample of normal
star-forming
galaxies at $z\sim1.1$ as part of the PAHSPECS program. To extract emission from Polycyclic Aromatic Hydrocarbon (PAH) features, we forward model the data cubes with non-parametric spatial distributions, accounting for convolution with the PSF. With this method we are able to recover accurate spatial profiles of the 3.3 $\mu$m, 6.2 $\mu$m, 7.7 $\mu$m, 11.3 $\mu$m PAHs and [ArII] (6.98 $\mu$m) emission and produce PAH ratio maps at
cosmic noon. From the PAH ratio maps we find that PAHs become larger and more neutral with increasing galactocentric radius, which is the opposite of trends in local
galaxies, indicating radial ISM gradients in normal
star-forming
galaxies are different at
cosmic noon. Through spatially resolved SED fitting of HST and JWST photometry we measure the UV radiation field hardness through the intrinsic ratio of UV to optical flux and find the 3.3/11.3 PAH ratio to decrease with increasing hardness and the 11.3/7.7 to increase. This may suggest photo-destruction of small/ionized PAHs is driving the observed PAH ratio trends and may explain the overall lower 3.3/11.3 PAH at
cosmic noon compared to the local universe. This work demonstrates that PAH properties hold crucial information on the resolved ISM physics of
galaxies at
cosmic noon.
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All authors Fergus R. Donnan, Karin Sandstrom, Irene Shivaei, Leindert A. Boogaard, Tanio Díaz-Santos, Cristina M. Lofaro, Román Fernández Aranda, Manuel Aravena, Roberto Decarli, Hanae Inami, Pablo G. Pérez-González, Gergö Popping, Paul P. van der Werf
High Energy Astrophysical Phenomena
A Joint Optimal Search for Gravitational Waves from Resolved and Unresolved Supermassive Binary Black Holes with Pulsar Timing Arrays
Boris Goncharov, Gabriela Sato-Polito, Xiaoming Bi et al. (+1 more)
We introduce, from first principles, a joint model of the gravitational wave background (GWB) and brightest supermassive black hole binary (SMBHB) sources that may be individually resolvable in
Pulsar Timing Array (PTA) searches for gravitational waves. We propose the characteristic number of SMBHB sources, $N_{\rm c}$, as a detection statistic for the astrophysical origin of the GWB. We then demonstrate how the brightest SMBHBs assist in resolving $N_{\rm c}$. Applying our method to the simulated NANOGrav 15-year data, which replicates all aspects of real data's known noise, observations, and the inferred GWB power spectrum, we demonstrate direct astrophysical limits on the strain amplitude of individually resolvable SMBHBs. We find that 21 of 114 SMBHB candidates from active
galactic nuclei observations are in tension with the NANOGrav's observations. In contrast, only one candidate is in tension with the NANOGrav data based on the upper limits reported in the original analysis. Constraining the Poisson-specific characteristic number of SMBHBs, $N_{\rm c}$, at ${\rm yr}^{-1}$, we outline implications for the population properties of SMBHBs. Based on our new model applied to the simulated NANOGrav data, we calculate the probability of detecting GWs from isolated SMBHB in the 15-year data to be 2% at the ${\rm SNR}=5$ level. Our projection towards the expected NANOGrav 20-year data suggests an increase to 5%. With this, we estimate the probability of finding an outlier with an SNR of 2 in the NANOGrav 20-year data to be $40\%$.
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All authors Boris Goncharov, Gabriela Sato-Polito, Xiaoming Bi, Matias Zaldarriaga
Astrophysics of Galaxies
PAHSPECS: Polycyclic aromatic hydrocarbon properties at cosmic noon with JWST/MIRI MRS
Cristina Maria Lofaro, Tanio Díaz Santos, Irene Shivaei et al. (+13 more)
Context.
Cosmic noon (z ~ 1-3) marks the peak of the
cosmic star-formation rate density, when
dust-obscured
star formation dominated
galaxy growth. Mid-infrared spectroscopy probes the interstellar medium through PAH emission, whose band ratios trace PAH charge, size, and local radiation-field conditions. Aims. We characterize the PAH properties of five z ~ 1.1
star-forming
galaxies from the PAHSPECS survey and investigate how their PAH luminosities and band ratios relate to global
galaxy properties. We compare them with local luminous infrared
galaxies (LIRGs) to assess whether PAH emission at
cosmic noon differs from that nearby. Methods. We analyze JWST/MIRI MRS observations of five ASPECS
galaxies in the HUDF. Integrated spectra are extracted with wavelength-dependent apertures and modeled with CAFE, including ancillary photometry to constrain the
dust emission.
Stellar masses and SFRs are derived with Prospector. Results. Compared to local LIRGs, most PAHSPECS sources show higher 6.2/7.7 and lower 11.3/7.7 ratios, suggesting an ionized PAH component weighted toward smaller grains. The 3.3/11.3 ratio is less constrained, since the 3.3 micron feature is detected in only two sources. Within the sample, 11.3/7.7 increases with sSFR and
star-formation surface density, while 6.2/7.7 decreases with sSFR, consistent with preferential processing of small ionized PAH carriers. ASPECS-15, the AGN-hosting source, has the lowest 6.2/7.7 ratio and highest sSFR, suggesting a reduced contribution from small PAHs, potentially due to AGN activity. The 7.7 micron luminosity follows the local L7.7-SFR relation, supporting its use as a
star-formation tracer at z ~ 1. Conclusions. PAH emission at
cosmic noon appears shaped by different ISM conditions than in nearby starburst
galaxies, likely reflecting more intense radiation fields, while the 7.7 micron feature remains a robust SFR tracer.
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All authors Cristina Maria Lofaro, Tanio Díaz Santos, Irene Shivaei, Leindert A. Boogaard, Karin Sandstrom, Fergus R. Donnan, Manuel Aravena, Pablo G. Pérez-González, Román Fernández Aranda, Roberto Decarli, Frédéric Galliano, Hanae Inami, Göran Östlin, Gergö Popping, Paul van der Werf, Fabian Walter
Astrophysics of Galaxies
An extreme ram-pressure stripping event in a protocluster at redshift 4.3
Dazhi Zhou, Scott C. Chapman, Manuel Aravena et al. (+16 more)
In the nearby Universe, the environment plays a crucial role in suppressing
star formation in dense regions. In particular, ram-pressure stripping (RPS) is a major mechanism for removing gas from
galaxies in clusters, occurring when
galaxies travel through a dense hot atmosphere and leave trailing gaseous wakes. By depleting the cold gas reservoir, RPS can drive outside-in quenching and is therefore thought to be an important route for transforming cluster
galaxies. At earlier times, however, the hot atmosphere in protoclusters is expected to be immature, so environmental effects are commonly assumed to be dominated by gravitational interactions. Here we report ALMA and JWST observations of SPT2349$-$56-C26 (hereafter C26), a massive
galaxy experiencing an extreme RPS event in the SPT2349$-$56 protocluster at $z\,{=}\,4.3$. More than half of the [CII]-traced cold gas lies outside its
stellar body, with the emission peak offset by 6 kpc. These observations show that RPS can remove most of the cold gas from massive
galaxies in dense protocluster cores as early as $z\,{=}\,4.3$, providing a direct hydrodynamic pathway for environmental quenching at $z\,{>}\,4$.
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All authors Dazhi Zhou, Scott C. Chapman, Manuel Aravena, Roger Deane, Anthony H. Gonzalez, Ryley Hill, Nicholas LeVar, Matthew A. Malkan, Adam Muzzin, Nan Zhang, Kedar A. Phadke, Vismaya R. Pillai, Manuel Solimano, Justin S. Spilker, Nikolaus Sulzenauer, Joaquin D. Vieira, David Vizgan, George C. P. Wang, Axel Weiss
Cosmology and Nongalactic Astrophysics
Field-level vs summaries: convergence of information in non-Gaussian density fields
Ivana Nikolac, Fabian Schmidt and Beatriz Tucci
We elucidate the sources of information gain in weakly non-Gaussian cosmological fields at the field- vs. summary-statistic-level in a controlled setting. Specifically, we compare field-level inference (FLI) with the standard power spectrum plus bispectrum (P${+}$B), and a family of composite-operator correlators (OCs) built from auto- and cross-spectra of local powers of the
galaxy density field. The forward model is a linear density field with a single local quadratic coupling $\lambda$ and Gaussian noise; this minimal nonlinear setup interpolates between a purely Gaussian
dataset ($\lambda=0$) and a non-Gaussian one ($\lambda\sim 1$), while keeping the analytical structure tractable. FLI is performed by jointly sampling the initial conditions, bias and noise parameters via MCMC; the summary posteriors are obtained with simulation-based inference (SBI) as well as Fisher estimates. In the Gaussian limit, the P${+}$B, OCs and FLI yield equivalent constraints, in agreement with the perturbative expectation. As the nonlinear coupling $\lambda$ increases, the summary-based uncertainties on the model parameters grow faster than the FLI ones, leading to an increasing information loss for a fixed set of summaries. This loss is largely, but not completely, recovered by adding OCs corresponding to up to the 6-point function. The information loss over FLI becomes even more pronounced for lower-noise data, where summaries corresponding to up to the 6-point function still capture significantly less information than the field.
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Earth and Planetary Astrophysics
Ice Giants Revisited: Uranus and Neptune as Magma Ocean Worlds
Edward D. Young, Sarah P. Marcum, Aaron Werlen et al. (+1 more)
Uranus and Neptune are commonly interpreted as volatile-rich "ice
giants", an assumption that underpins most interior models. Here we show that their observed radii, bulk densities, gravitational harmonics, normalized moments of inertia, intrinsic luminosities, and key features of their atmospheric compositions are consistent with interiors comprising supercritical, hydrogen-rich magma oceans overlain by H2-rich envelopes. Our results, based on three fit parameters for each
planet, provide a parsimonious explanation for the structures, thermal states, and atmospheric chemistries of Uranus and Neptune. We find that the
Solar System's ice
giants are better understood as magma-ocean
giants, with origins parallel to those of sub-Neptune gas-
dwarf planets. A continuum among gas
dwarf planets permits Neptune and Uranus to serve as accessible, data-driven test cases for structure models and material properties used to understand sub-Neptunes.
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All authors Edward D. Young, Sarah P. Marcum, Aaron Werlen, Paula N. Wulff
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Beyond Plane Waves: Coherent Network Response to Collimated Gravitational-Wave Wavepackets
S. D. Campos
We present a paraxial wavepacket model for structured, collimated gravitational-wave bursts and derive the coherent response of detector networks to these signals. For current terrestrial baselines such as LIGO-Virgo, analytic mismatch estimates confirm that the paraxial wavepacket model waveforms are effectively indistinguishable from standard sine-Gaussian bursts, validating the robustness of the plane-wave approximation in this regime. However, we identify a physical scaling regime relevant to third-generation networks and
galactic-scale
Pulsar Timing Arrays in which finite transverse structure-motivated by wave-optics
lensing or ultra-relativistic beaming induces non-negligible
geometric phase shifts. A toy event-level Monte Carlo study compares a standard burst-search ranking with a paraxial wavepacket model-constrained statistic that penalizes
geometric inconsistencies across detectors. In this controlled setup, the model prior yields an illustrative factor of $\sim 3$-$4$ gain in detection efficiency at a fixed false-alarm rate, while maintaining performance on plane-wave-like signals. These results suggest that paraxial corrections may provide a necessary metrological framework for signal discrimination and unbiased parameter estimation in future
cosmic-scale observations.
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Instrumentation and Methods for Astrophysics
Resolving the smallest scales of massive star formation: A case for next-generation thermal-infrared interferometers
Emma Bordier, Evgenia Koumpia, Lucas Labadie et al. (+3 more)
This white paper was submitted to the European Southern Observatory (ESO) as part of the "Expanding horizons: transforming astronomy in the 2040s" call. Understanding how massive
stars assemble their mass is a major astrophysical challenge, primarily because the critical
accretion, ejection, and fragmentation processes occurring within the innermost 100 au remain largely inaccessible. Current facilities, such as ALMA and near-infrared interferometers, either lack the resolution to probe the compact high-mass
star-disk interaction zone or are severely hindered by high extinction and marginal spectral resolution. To bridge this observational gap, this white paper advocates for next-generation thermal-infrared interferometers operating in the L, M, N, and Q bands to directly observe warm
dust, hot gas, and embedded protostars at sub-milliarcsecond scales. These advanced capabilities will provide unprecedented access to a rich molecular inventory and spatially resolved spectroscopy, which are crucial for disentangling
accretion streams, disk winds, and fragmentation mechanisms on dynamical timescales. We propose that developing heterodyne-based, long-baseline interferometry at high, dry sites represents the most transformative and realistic pathway to finally unveil the complete picture of massive
star formation.
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All authors Emma Bordier, Evgenia Koumpia, Lucas Labadie, Joel Sanchez-Bermudez, Alvaro Sanchez-Monge, Jean-Philippe Berger
High Energy Astrophysical Phenomena
X-ray eclipse tomography: Resolving the extent of X-ray-emitting region(s) in the Seyfert galaxy ESO362-G18
Laura Rueda-Nieto, Beatriz Agís-González and Giovanni Miniutti
X-ray spectral variability in active
galactic nuclei (AGNs) can be either intrinsic or caused by external processes, such as variable absorption. Several transient occultation events from individual clouds or X-ray eclipses have been identified in a number of AGNs in the past two decades. We report results from the analysis of two Swift monitoring campaigns of the Seyfert
galaxy ESO 362-G18, a changing-look AGN that showed transitions between optical spectral types 1.5 and 1.9 in the past, most likely induced by variable absorption. We identified two X-ray eclipses during the first Swift campaign, one of which we were able to follow almost entirely from ingress to egress. We used time-resolved spectroscopy to follow the
evolution of the X-ray spectrum with time in order to derive the properties of the absorbing cloud and the size of the main X-ray-emitting region. The cloud is located towards the innermost
dust sublimation zone, intermediate between the
dust-free broad-line region and the dusty
torus. The X-ray-emitting region is confined within 35 gravitational radii (Rg) from the centre. A deeper analysis indicated that the eclipsing cloud likely comprises a denser core and a more tenuous atmosphere. We were also able to estimate the size of the soft excess and hot corona X-ray-emitting regions separately. These are two of the most relevant continuum components in the X-ray spectra of unobscured AGNs. Our analysis suggests that the soft-excess-emitting region is 50% more extended than the hot corona one. However, it appears to co-exist with and is not replaced by the hot corona one in the innermost 30 Rg. Our results highlight the potential of X-ray eclipse
tomography for providing a clearer view of the innermost
accretion flow geometry and of the AGN surroundings out to the
torus scale.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
The free boundary problem in general relativity
Kostas Tzanavaris, Latham Boyle and Neil Turok
We study the action principle for space-times whose boundary is singular. We suggest that it is natural to treat the singularity as a free boundary, where the variation is unconstrained. Demanding that the action is stationary under such free variations then implies certain (on-shell) boundary conditions at the singularity. We derive these boundary conditions for the case of Einstein
gravity coupled to matter and show that, when applied to an initial spacelike singularity, they exclude Kasner-like or BKL space-times, but admit conformally regular space-times (including FLRW models) sourced by fluids satisfying $0 \leq P < \rho$. For standard hot big bang FLRW cosmologies, the admissible linear (scalar, vector, tensor) perturbations satisfy reflecting boundary conditions at the bang, in agreement with large-scale cosmological observations.
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High Energy Astrophysical Phenomena
Detailed Timing, Spectral, and Polarimetric Analysis of Magnetar 1RXS J170849.0-400910
Rachael Stewart, George Younes, Alice Harding et al. (+5 more)
We present a broadband timing, spectral, and polarimetric study of the magnetar 1RXS~J170849.0-400910 using XMM-Newton, NuSTAR, and IXPE. The pulse morphology evolves strongly across 0.5-70 keV. Below 3 keV, the emission is dominated by a broad soft pulse with a leading shoulder that develops into a faint interpulse near 3 keV, while the pulse fraction remains $\approx$25%. The profile becomes increasingly double-peaked between 3 and 20 keV and returns to a single peak at higher energies. The pulse fraction dips to $\sim$20% near 4 keV and rises to $\sim$42% above 25 keV. The phase-averaged spectrum is well described by an absorbed blackbody plus two power-laws, with $kT=0.468\pm0.003$ keV, $\Gamma_{\rm soft}=2.63\pm0.04$, and $\Gamma_{\rm hard}=0.5\pm0.1$. Phase-resolved spectroscopy reveals distinct soft and hard pulse components. The thermal modulation is driven primarily by a factor of $\sim$5 variation in projected emitting area, whereas the soft power-law exhibits two peaks with different phase and energy
evolution, suggesting distinct emission regions or mechanisms. The 10-70 keV flux is strongly anticorrelated with the soft power-law
photon index, linking spectral hardening to the hard pulse. The polarization degree also varies strongly with phase and energy. In the 2-3 keV band, it is anticorrelated with the intensity profile, consistent with magnetized-atmosphere emission, whereas in the 4-8 keV band it reaches $64\pm10$% during the nonthermal power-law-dominated peak. This high polarization can be reproduced by magnetospheric
quantum pair-synchrotron emission. Together, these results reveal an intricate, phase-dependent superposition of emitting regions and radiative processes whose complexity emerges only through broadband, phase-resolved spectropolarimetry.
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All authors Rachael Stewart, George Younes, Alice Harding, Hoa Dinh Thi, Matthew Baring, Zorawar Wadiasingh, Michela Negro, Alex Van Kooten
Instrumentation and Methods for Astrophysics
Querying an astronomical database using large language models: the ALeRCE text-to-SQL system
P.A. Estevez, J.Espejo-Moreira, S. Sanfeliu-Alvarez et al. (+10 more)
We develop a text-to-SQL (structured query
language) system based on large
language models (LLMs) using in-context learning and apply it to the Automatic Learning for the Rapid Classification of Events (ALeRCE) astronomical database. ALeRCE is a community broker for the Zwicky Transient Facility and the Vera C. Rubin Observatory. The system enables users to query the database in natural
language (NL) and generates executable SQL queries. To develop and evaluate the system, we constructed a
dataset of 110 NL/SQL pairs. We propose a step-by-step generation framework comprising four modules: schema linking, query classification,
prompt decomposition, and self-correction. The performance of thirteen LLMs is evaluated using in-context learning and
prompt engineering techniques. Text-to-SQL performance is assessed using the perfect-match (PM) rate for row identifiers (e.g., object identifiers) and column identifiers (i.e., column names). The proposed step-by-step framework consistently outperforms a direct-inference baseline, while the self-correction module consistently reduces execution errors. For Claude Opus 4.6, PM performance on row (column) identifiers is high for simple queries, reaching 0.97 (0.94), and decreases with query complexity to 0.44 (0.72) for medium queries and 0.59 (0.49) for hard queries. Among the thirteen evaluated models, the best-performing LLMs for the text-to-SQL task are Claude Opus 4.6, Gemini 2.5 Pro, Gemini 3 Flash, and GPT-5.2-Codex.
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All authors P.A. Estevez, J.Espejo-Moreira, S. Sanfeliu-Alvarez, F. Forster, A. M. Munoz Arancibia, G. Cabrera-Vives, F. E. Bauer, A. Bayo, M. Catelan, R. Dastidar, L. Hernandez-Garcia, J.A. Intriago, G. Pignata
High Energy Astrophysical Phenomena
Polarized emission of orbiting hot-spots near Sagittarius A*: effects of electromagnetic interaction
Abylaikhan Tlemissov, Arman Tursunov and Maciek Wielgus
We investigate the polarimetric signatures of orbiting hot-spots around a Schwarzschild black hole in the presence of an external
magnetic field, accounting for the electromagnetic interaction between the charged emitter and the field. Using a general-relativistic model that incorporates synchrotron emission and ray-tracing of light propagation, we analyze how the electromagnetic interaction parameter modifies the observed polarization patterns, with particular emphasis on the behavior of the electric vector position angle (EVPA) and the time-evolving polarization loops in the $Q$-$U$ plane. Applying the model to millimeter wavelength ALMA observations of Sagittarius~A*, we explore the parameter space that best reproduces the asymmetry, time ratio, and area ratio of the observed polarization loops. We find that the inclusion of a small positive interaction parameter increases the
symmetry of the loops and the time ratio, while a negative
magnetic parameter introduces strong asymmetry and fails to reproduce the data. Our results indicate that electromagnetic interaction can lead to ambiguity in the estimation of the system parameters such as orbital inclination or hot-spot velocity.
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Astrophysics of Galaxies
The ultra-deep HI radial profiles of late-type galaxies from MHONGOOSE
S. Veronese, W. J. G. de Blok, E. Brinks et al. (+4 more)
Galaxy discs have a finite extent, yet how and where their neutral atomic hydrogen (HI) components end is not fully understood. The existence of a break in the HI disc at column densities of $\sim10^{19}$ cm$^{-2}$ has been debated since early 21-cm observations of the spiral
galaxy NGC 3198. We present the HI radial profiles of 16
star-forming, late-type
galaxies from the MeerKAT HI Observations of Nearby
Galactic Objects: Observing Southern Emitters (MHONGOOSE) survey spanning a range of HI mass from $10^{7}$ M$_\odot$ to $10^{10}$ M$_\odot$. We probed via spectral stacking their HI discs down to inclination-corrected column densities of a few times $10^{17}$ cm$^{-2}$ at kpc resolution. The HI radial profiles of high-mass (M$_{\rm {HI}}>10^{9}$ M$_\odot$)
galaxies are characterised by a inner plateau, followed by a knee at column densities of $\sim5\times10^{20}$ cm$^{-2}$, but no edges are unambiguously identified. The HI radial profiles of low-mass (M$_{\rm {HI}}>10^{9}$ M$_\odot$)
galaxies shows a steeper decline and also no edges. We found that the profiles are self-similar when normalised to the radius at which a mass surface density of 0.01 M$_\odot$ pc$^{-2}$ is reached, in agreement with recent literature results, but we also found a possible correlation between the normalisation radius and the environment, suggesting that environment contributes to the shaping of the HI distribution in
galaxies. The emerging picture is that the diverse morphology of the HI radial profiles is difficult to interpret, and future studies with a larger sample are necessary for quantifying the contribution of internal and external processes acting at different levels for different
galaxies.
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All authors S. Veronese, W. J. G. de Blok, E. Brinks, D. Kleiner, S. Kurapati, J. Healy, F. M. Maccagni
Earth and Planetary Astrophysics
Effect of tidal gravity and planetary rotation on the retrieved atmospheric abundances of close-in exoplanets
K. Arnav and Gopal Hazra
Most modern atmospheric
retrievals adopt the simplifying assumption that the planetary atmosphere endures no planetary rotation and
stellar tidal effect. However, for tidally locked close-in
exoplanets, the gravitational influence of the host
star and the rapid rotation of the
planet can significantly modify the effective
gravity, leading to changes in the atmospheric scale height and mixing ratios of molecular abundances. In this work, we develop a combined framework to include these rotation and
tidal effects into a forward and
retrieval model to study how they affect the molecular abundances of close-in
exoplanets. We specifically apply our model to the
planet WASP-12b, observed with HST, and WASP-39b, observed with JWST, and investigate how atmospheric
retrieval parameters change when
tidal and centrifugal corrections to
gravity are included. The forward model calculation for strongly affected
gravity due to
tidal and rotation effects in WASP-12b shows an increment in transit depth in the range of 150-500 ppm for major molecules in the atmosphere, whereas for WASP-39b with small
gravity reduction shows variations of 60- 180 ppm. The atmospheric
retrievals for WASP-12b using HST and WASP-39b using JWST transmission spectra with and without effective
gravity corrections show an increment in the retrieved molecular abundances. A systematic study by reducing the effective
gravity by 20%, 30% and an extreme value 50% for WASP-39b shows increasing changes in the inferred log-mixing ratios of various molecules. Our results show a similar trend with non-isothermal P-T profiles, but cloudy models suppress the combined effect of rotation and
tidal gravity.
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Cosmology and Nongalactic Astrophysics
Large primordial non-Gaussianity from transient turns in Higgs-$R^2$ inflation
Flavio Pineda and Luis O. Pimentel
We investigate the generation of
primordial non-Gaussianities in multifield
Higgs–$R^2$ inflation, focusing on the effects of transient turning trajectories in the
hyperbolic field space
manifold. We compute the full bispectrum without relying on slow-roll or local approximations and follow the complete superhorizon
evolution of
curvature and isocurvature perturbations. We show that transient turns efficiently transfer isocurvature fluctuations into the adiabatic sector, generating sizeable local non-Gaussianities. For a
benchmark Higgs nonminimal coupling $\xi_h = 0.1$ and quartic coupling $\lambda = 10^{-10}$, we obtain $f_{\rm NL}^{\rm loc}\simeq -17.7$. As the
Higgs nonminimal coupling increases, the turning rate is progressively suppressed and the model approaches the effective single-field attractor, recovering the Maldacena consistency relation $f_{\rm NL}\rightarrow 0.0159$. Comparing our predictions with current CMB constraints, we find that
primordial non-Gaussianity provides a sensitive probe of the
Higgs nonminimal coupling and can significantly restrict the viable parameter space of the model.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Ultra-High-Energy Cosmic Ray Boosted Relic Neutrinos
Jiajie Zhang and Jiajun Liao
Ultra-high-energy
cosmic rays (UHECRs) can boost relic
neutrinos to high energies through Standard Model (SM) neutral-current interactions, providing an indirect probe of the
cosmic neutrino background (C$\nu$B). In this work, we perform a systematic study of the diffuse UHECR-boosted C$\nu$B flux including elastic
neutrino-nucleon scattering (ES), coherent elastic
neutrino-
nucleus scattering (COH), incoherent
neutrino-
nucleus scattering (INCOH),
baryon-resonance production (RES), and deep inelastic scattering (DIS). For the UHECR flux, we use mixed-composition spectra obtained from the UHECR propagation code PriNCe and from the H3a and H4a implementations of the Hillas model, together with SFR, QSO and GRB source
evolution models. We find a clear hierarchy of scattering channels in boosted
neutrino energy. The coherent scattering dominates at low-energy
neutrino flux for heavy
nuclear component, while ES and INCOH become important once individual nucleons are resolved. The RES channel gives a non-negligible contribution in the high-energy region, and DIS appears only at the highest energies and is most visible for the H4a models. Using current IceCube and Pierre Auger Observatory data, we derive upper limits on the C$\nu$B overdensity. Our results show that reliable predictions of the UHECR-boosted C$\nu$B signal require a combined treatment of the relevant SM scattering channels, UHECR composition, source
evolution and the
neutrino mass spectrum.
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Astrophysics of Galaxies
Variability in Cosmological Hydrodynamical Simulations: how Stochastic Processes, Numerical Effects, and Reproducibility Limits impact Predictability
Chaitra, Antonio Ragagnin, Milena Valentini et al. (+3 more)
Cosmological hydrodynamical simulations are powerful tools for studying
galaxy formation, yet their predictive precision is limited by
stochastic variability and numerical uncertainty. We quantify this variability using four identical realizations of a zoom-in
galaxy-cluster simulation evolved with OpenGadget3 under tightly controlled compiler, library, and hardware settings. Variability is measured through the properties of matched
galaxies across repeated runs, including a mixed linear model that separates run-to-run variation from within-run noise. Variations of approximately $10$-$25\%$ are found in
galaxy dark matter and
stellar masses for the baseline simulations. The variability trending above the shot-noise floor reflects the combined effects of
stochastic star formation and feedback regulation, and is further amplified when black hole physics is included. Furthermore, our results indicate that feedback acts to regulate variability, reducing scatter in both
stellar and black hole masses. Our inference from run-to-run variation indicates a noise-dominated regime that remains statistically reproducible, despite individual realization differences. These results establish baseline, noise-dominated variability estimates at low resolution, demonstrate how feedback modulates predictability, and provide a statistical framework for future studies of reproducibility in cosmological hydrodynamical simulations.
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All authors Chaitra, Antonio Ragagnin, Milena Valentini, Giuseppe Murante, Stefano Borgani, Giuliano Taffoni
High Energy Astrophysical Phenomena
The Chirp-Mass Ladder: A New Rung Emerges
Vaibhav Tiwari
We study the binary black hole (BBH) population observed through gravitational waves (GWs) using 256 events from the latest release of GWTC-5.0. The inferred chirp-mass distribution shows prominent peaks at approximately $7.5M_{\odot}$, $14M_{\odot}$, and $27M_{\odot}$, with subsequent peaks spaced by approximately a factor of two. A parsimonious explanation for this structured distribution is a hierarchical merger scenario, in which the first peak arises from mergers of black holes of
stellar origin, and higher-mass peaks arise from repeated mergers. Notably, with the addition of new observations, an intermediate peak near $19M_{\odot}$ emerges. This feature was anticipated in earlier work as a consequence of intergenerational mergers involving second- and third-generation (G) black holes, highlighting the predictive expectations of the hierarchical-merger interpretation. Furthermore, two groups of $1G+2G$ mergers recently reported in separate studies can be understood as distinct rungs—$1G+2G$ and $3G+4G$—within this hierarchical chirp-mass ladder, a unification that describes both
spin transitions with a single mechanism. Although we observe expected correlations between mass ratios and
spins in multiple events across the mass range, the lack of clear signatures across all rungs invites investigation into the role of hierarchical mergers in shaping the BBH population.
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Instrumentation and Methods for Astrophysics
Sustainability as a design parameter in the early development of the Wide-field Spectroscopic Telescope
L. Fréour, E. Burtin, R. Bacon et al. (+13 more)
The proposed Wide-field Spectroscopic
Telescope, a next-generation
telescope facility with a 12-meter primary mirror that may be operational in the 2040s, is integrating sustainable considerations from the early design stage. Our preliminary analysis identifies two primary sources of environmental impact that can be mitigated during the design process. First, we are conducting a life-cycle assessment (LCA) to quantify the environmental impact of the ~250 spectrographs and the detector cooling systems across the
telescope's three instruments, from construction through operation. The carbon footprint estimated through this LCA has been included as a trade-off parameter in the design choices. Second, the WST is expected to produce 1-3 PB/year, requiring careful evaluation of data processing and storage strategies. We explore approaches to monitoring and reducing the carbon footprint associated with data management. Bringing environmental factors into the design process from the start gives us the chance to weigh sustainability alongside scientific performance and cost. By treating the carbon footprint as a core design consideration, we aim to make progress toward more responsible astronomy.
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All authors L. Fréour, E. Burtin, R. Bacon, B. Ziegler, S. Randich, A. Pecontal, P. M. Weilbacher, C. Cudennec, D. Buffat, S. D'Auria, A. Meoli, L. P. Cassarà, P. Dierickx, V. Mainieri, P. Franzetti, D. Lee
High Energy Astrophysical Phenomena
A Semi-Analytical Loss Cone Theory for Tidal Disruption Event Rates Around Kerr Black Holes
Wenkang Xin
A
tidal disruption event (TDE) occurs when a
star is scattered onto a near-radial orbit and is torn apart by a black hole (BH)'s
tidal field. The angular momentum threshold for disruption is set by general relativistic
tidal dynamics, while the supply of
stars to the disruption zone is governed by Newtonian
stellar dynamics. A spinning BH breaks the spherical
symmetry of the disruption boundary, so a
star's survival depends on both the magnitude and the orientation of its angular momentum. Existing treatments either assume a non-spinning BH or rely on numerical simulations of spinning BHs. We develop the first semi analytical framework that incorporates
spin-dependent loss cone boundaries into TDE rate theory. Using a novel
tidal tensor formalism, we compute inclination-dependent thresholds for
tidal disruption and direct capture by the event horizon. We then revisit the classical one dimensional loss cone problem with nested disruption and capture boundaries, deriving a closed form capture fraction valid across all loss cone regimes. Finally, we formulate a two dimensional Fokker–Planck equation describing simultaneous
diffusion in angular momentum magnitude and orientation. Through a perturbative treatment, we demonstrate that while the Kerr disruption boundary induces a first-order bias favouring the disruption of retrograde
stars, the global TDE rate is remarkably insensitive to black hole
spin. This approach offers a tractable route to including
spin and orbital inclination in population-level TDE studies.
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Earth and Planetary Astrophysics
Transit timing and starspot-induced transit depth variations in the $\sim$17 Myr old HIP 67522 system
H. Chakraborty, M. Lendl, A. Nigioni et al. (+27 more)
HIP 67522 is a one of the youngest multi-planetary systems discovered to date. The 17 Myr-old, Sun-like
star is part of the Scorpius-Centarus OB association and is known to host two Saturn-sized
planets in near 2:1 mean motion resonance. We analysed photometric transits observed with the CHaracterising
ExOPlanet Satellite (CHEOPS), the Transiting
Exoplanets Survey Satellite (TESS) and multiple ground-based facilities to search for transit timing variations induced by
planet-
planet gravitational interactions, as well as transit depth variations, linked with the changing coverage of active regions on the
stellar surface. We do not detect any transit timing variations for HIP 67522 b exceeding two minutes, contrary to previous results from the James Webb Space
Telescope. In addition, we found that the observed transit depth of
planet b changes strongly over time, with a >30% variation in amplitude. The high sensitivity and blue bandpass of the CHEOPS satellite also enabled us to identify multiple starspot crossings and measure their properties, including spot temperatures and sizes. We also measured the shear of the host
star's differential rotation by modelling the out-of-transit photometric variability and concluded that HIP 67522 exhibits a supersolar differential rotation. Based on internal structure models and
planet formation simulations, we find that HIP 67522 b likely have more than 20% of their mass made of gaseous envelopes at their current age. Evolutionary simulations further indicate that both
planets in the system will experience significant photoevaporation, evolving into either Earth size
planets with completely stripped atmospheres or sub-Neptune-sized
planets.
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All authors H. Chakraborty, M. Lendl, A. Nigioni, J.A. Egger, J.M. Almenara, M.P. Battley, A.G.M. Pietrow, J. Venturini, A. Heitzmann, B. Akinsanmi, I. Apergis, D. Bayliss, J.P. Faria, A.D. Feinstein, J.F. Fernández, E. Fontanet, E. Gillen, E. Ilin, T. Jestin, J.S. Jenkins, E.J. Lößnitz, J. McCormac, C. Modrasini, F. Neiradiaz, H.P. Osborn, D.J.M. Petit dit de la Roche, S. Saha, A.M.S. Smith, S. Ulmer-Moll, P.J. Wheatley
Instrumentation and Methods for Astrophysics
On-sky binary source hypothesis testing beyond the diffraction limit using spatial mode demultiplexing based detection
John S. Wallis, Ayden S. McCann, Joshua J. Collier et al. (+4 more)
Improving the resolution of
telescope systems will provide the opportunity to study new physical phenomena in previously unobserved environments. Spatial mode de-multiplexing (SPADE) based imaging is a promising and rapidly evolving technique for pushing the resolution of optical
telescopes beyond the diffraction limit. A key application of this technique is for near-optimal hypothesis testing for the presence of secondary and extended sources in the sub-diffraction regime. We present the first demonstration of a binary-SPADE based hypothesis testing instrument deployed on-sky. In our proof-of-principle experiment, based on mode demultiplexing with a double clad fiber coupler, we demonstrate detection of a binary
star system separated below the diffraction limit. We perform measurements in the
photon-starved regime where no image can be formed by traditional direct imaging. We find the scaling of the system's type II error rate (the “binary source miss" chance) was heavily limited by unbalanced loss in our double-clad fiber coupler when compared to the idealized
quantum limits. Despite this the evaluated type II error is always lower than a perfect direct imaging measurement. We expect that if this instrument is scaled to larger aperture
telescope systems the effects of atmospheric
turbulence will further degrade this system's performance.
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All authors John S. Wallis, Ayden S. McCann, Joshua J. Collier, Lilani D. Toms-Hardman, Alex M. Frost, Benjamin P. Dix-Matthews, David R. Gozzard
High Energy Astrophysical Phenomena
Discovery of a quasi-periodic oscillation non-harmonically related to the Type-C QPO in the hard intermedidate state of MAXI J1820+070
Pei Jin, Mariano Méndez, Federico García et al. (+2 more)
We present a detailed timing analysis of the transition from the hard-intermediate state (HIMS) to the soft-intermediate state (SIMS) in MAXI J1820+070 using NICER observations. This transition is marked by a sharp drop of the broadband noise across both the soft and hard X-ray bands, the disappearance of the Type-C quasi-periodic oscillation (QPO), the quenching of the steady, optically thick, compact jet, the appearance of a Type-B QPO, and the detection of discrete, optically thin,
radio ejections. For the first time, we detect a QPO at 3.5-5.9 Hz in the 2-12 keV power density spectrum of MAXI J1820+070 roughly half a day before the transition, which appears to evolve smoothly into the Type-B QPO observed immediately after the transition. The location of this additional QPO component in the broadband rms vs. QPO frequency plot is consistent with that of the Type-B QPOs in GX 339-4 and GRO J1655-40, suggesting a possible connection between this additional QPO in the HIMS and the Type-B QPO in the SIMS. This result, together with recent findings in Swift J1727.8-1613, suggests that QPOs with these characteristics can emerge prior to the HIMS-to-SIMS transition and are not confined exclusively to the SIMS. If this additional QPO feature is the precursor of the Type-B QPO in the SIMS, its presence before the transition, whereas the bright discrete, optically thin,
radio ejections appear at the transition, would imply that there may be no direct physical connection between the Type-B QPO and the discrete
radio ejections. Our results further suggest a link between the disappearance of the Type-C QPO, the drop of the broadband noise, and the emergence of discrete
radio ejections at the HIMS-to-SIMS transition. We speculate that the simultaneous presence of such a QPO, non-harmonically related to the Type-C QPO in the HIMS, could be compatible with a spine-sheath
outflow structure.
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All authors Pei Jin, Mariano Méndez, Federico García, Diego Altamirano, Ruican Ma