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Physics Astrophysics Instrumentation and Methods for Astrophysics

astro-ph.IM Watch Instrumentation and Methods for Astrophysics

Thursday 8 October

Instrumentation and Methods for Astrophysics · Cross-listed from eess.SY

Reference-Filter-Driven Transition Probabilities for IMM-Based Satellite Maneuver Detection

Euiseok Han, Sangheon Choi and Seung-Hyun Kong

Maneuver detection of non-cooperative satellites is an essential task of space situational awareness. The interacting multiple model (IMM) filter has been applied to detect unannounced maneuvers, but the standard IMM assumes a fixed Markov transition probability matrix (TPM) that must be tuned without knowledge of the maneuver rate of the target. To avoid this tuning, adaptive-TPM approaches update the TPM online from statistics computed inside the IMM. However, these statistics already depend on the TPM through the mixing step, and this dependence forms a feedback loop. Under the dynamics mismatch of orbit tracking, the loop can keep the maneuver probability high in the absence of a maneuver or suppress its rise when a maneuver occurs. In this paper, the TPM is driven by the normalized innovation squared (NIS) of a reference coast filter that is not mixed with the IMM, and the NIS is mapped continuously to the coast-to-maneuver transition probability. The reference-driven IMM (RD-IMM) is evaluated with four space-based optical sensors tracking a geosynchronous target. RD-IMM detects small burns that the fixed-TPM IMM fails to detect, with few false declarations in maneuver-free runs, and avoids both failures of the closed-loop adaptation. Moreover, RD-IMM reduces the position error after a small in-track burn by more than 50% compared with the single-filter approaches.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Accounting for detector calibration uncertainty in black-hole ringdown analysis

Rowina S. Nathan, Shingo Hido, Neil Lu et al. (+3 more)

Detector calibration systematics can bias measurements of a remnant black hole's mass and spin, producing spurious evidence against general relativity if unaccounted for. The ringdown phase in the gravitational-wave signal produced by a binary black-hole merger encodes the remnant properties: at sufficiently late times, the signal is well described by a superposition of quasinormal modes, each with a frequency and damping time set only by the remnant mass and spin. Here we present two complementary approaches for analyzing the ringdown portion of the data to estimate the remnant mass and spin in the presence of a nonnegligible detector calibration error, using the quasinormal-mode rational filter (QNMRF). With a well-measured error, we apply the best-estimated calibration correction to the strain before conducting the standard analysis; with an unknown error, we instead jointly sample the remnant mass, spin and the frequency-dependent calibration error, marginalizing over an uncertainty prior. By injecting the numerical-relativity waveform SXS:BBH:0305 into colored detector noise, at a full-signal matched-filter signal-to-noise ratio of $\sim60$ and with simulated calibration errors of $\pm25\%$ in magnitude and $\pm25^\circ$ in phase, marginalizing over the calibration uncertainty recovers the true mass and spin within the 90% credible interval, whereas the estimated values are biased if the calibration errors are ignored. We apply the method to GW250207, an event recorded while the Hanford detector response was not well characterized, and recover a remnant consistent with the inspiral-merger-ringdown prediction using the ringdown portion alone, both by correcting for a best-estimated calibration error and by marginalizing over a broad uncertainty prior.
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All authors Rowina S. Nathan, Shingo Hido, Neil Lu, Mallika R. Sinha, Sizheng Ma, Ling Sun

Wednesday 7 October

Instrumentation and Methods for Astrophysics

DeepDISC on LSST Data Preview 1: Scene-Level Detection, Deblending, and Star/Galaxy Classification in the ECDFS and EDFS Fields

Prince Yadav, Yaswant Sai Ejjagiri, Xin Liu et al. (+2 more)

We present the first application of DeepDISC, a scene-level deep-learning framework, to real LSST data, using the Data Preview 1 (DP1) coadded images of the Extended Chandra Deep Field-South and the Euclid Deep Field-South fields. In a single pass, DeepDISC jointly detects, segments, and classifies sources as stars or galaxies, rather than treating these tasks as separate steps as in traditional pipelines. We warm-start from a model pretrained on LSST simulations and fine-tune it on DP1 six-band images, using the DP1 catalog's extendedness flag (point-like versus extended) as provisional class labels. The classification part of the network is then fine-tuned alone on a curated sample of stars and galaxies with spectroscopic, Gaia, and photometric identifications, so the final output is a star/galaxy classification. Fine-tuning on real DP1 observations substantially improves source recovery relative to the un-fine-tuned model, raising galaxy and star completeness from 40.2% and 13% to 84.2% and 49.1% under strict class-aware matching; under class-agnostic matching the fine-tuned model reaches 84.9% and 74.3%. On a common sample of sources that neither classifier saw in training, DeepDISC classifies to within about one percentage point of a published photometry-based Random Forest for the same field (97.4% vs. 98.5%); at fainter magnitudes DeepDISC labels more sources as stars than the Random Forest, and independent labels favor the Random Forest in most of these disagreements. Cross-matching to deeper HST/CANDELS imaging on a held-out footprint gives an unrecognized-blend fraction for DeepDISC of 14.9% (95% CI 12.5-17.8%), consistent with or modestly below the 18.0% we measure for the production DP1 catalog. This work establishes a baseline for DeepDISC on real LSST data and a foundation for self-supervised pretraining and for LSST Data Preview 2.
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All authors Prince Yadav, Yaswant Sai Ejjagiri, Xin Liu, Grant Merz, the LSST Dark Energy Science Collaboration

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.GA

Central stellar depletion in the Draco dwarf from Subaru photometry

Eduardo Vitral, Kyosuke S. Sato, Jorge Peñarrubia et al. (+2 more)

Dark matter subhaloes are a fundamental prediction of the standard cosmological model, but their low-mass population remains difficult to constrain observationally. Recent work has shown that interactions between subhaloes and dwarf spheroidal galaxies can induce large-scale, out-of-equilibrium fluctuations in their stellar surface density fields, identifiable through Fourier-based statistics. We apply this formalism to deep Subaru photometry of the Draco dwarf, extending previous tests to $\gtrsim\mathcal{O}(10^{4})$ resolved stars. We use artificial-star tests to assign completeness weights to individual stars and incorporate them into a discrete likelihood-based framework. Relative to a cored axisymmetric Plummer model, Draco shows radial corrugations that appear in the filtered normalised residuals as a central stellar depletion surrounded by a ring-like excess. The same feature appears in Fourier space as a low-frequency peak with a signal-to-noise ratio ${\rm S/N}=6.0$. Independently, fitting the surface density $\Sigma$ with an $\alpha\beta\gamma$ model yields ${\rm d}\Sigma/{\rm d}R>0$ at $>99.9\%$ confidence – i.e., a profile that decreases towards the centre. Although these signatures cannot yet be regarded as robust evidence for dark subhaloes, they suggest that central stellar depletion in dwarf galaxies may reflect genuine physical structure rather than crowding alone.
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All authors Eduardo Vitral, Kyosuke S. Sato, Jorge Peñarrubia, Sakurako Okamoto, Veronika Dornan

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.EP

Systematic non-compliance of satellite megaconstellations with IAU brightness limits

Jack Rayworth, Denis Vida, Pauline Barmby et al. (+7 more)

Satellite megaconstellations in low Earth orbit interfere with ground-based optical astronomy, but the scale of that interference has been hard to measure. Here we report an uncued photometric survey from a mid-northern latitude site in late 2024 which recorded some 25,000 tracks of 5,118 individual satellites to a limiting visual magnitude of +9.0. The observed population is systematically brighter than the altitude-adjusted limit of order seventh magnitude recommended by the International Astronomical Union Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (IAU CPS). Starlink satellites exceeded that limit on roughly a quarter of all geometrically possible passes, rocket bodies on about a fifth, and the emerging Guowang/Hulianwang constellation on more than half. OneWeb was the most compliant major operator (exceeding the IAU CPS limit on only about one in twenty possible passes), which shows that effective brightness mitigation is achievable with current technology. Satellite visibility is concentrated into the two hours after sunset and before sunrise and into limited regions of the sky. From the measured plane-of-sky satellite flux we predict that of order one in three 30 s twilight exposures at the Vera C. Rubin Observatory will carry a satellite trail.
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All authors Jack Rayworth, Denis Vida, Pauline Barmby, Peter G. Brown, Sarah Gallagher, Michael J. Mazur, David L. Clark, Maximilian Vovk, Stanimir Metchev, Lauchie Scott

Instrumentation and Methods for Astrophysics

Microwave Loss in Low-Temperature ICPCVD Silicon Nitride: Dependence on Precursor Ratio and RF Substrate Bias

H. Athreya, J. Cornelison, M. Mikhailov et al. (+5 more)

Low-loss dielectric films are an important component of superconducting circuits with applications ranging from quantum information to superconducting detectors for astrophysics. In millimeter-wave detector circuits, dielectric loss can be the limiting factor on efficiency and resonator performance. Some advantageous detector fabrication architectures require dielectric deposition at temperatures substantially lower than those conventionally used to achieve low dielectric loss. In this work, we characterize silicon nitride (SiN$_x$) films deposited by inductively coupled plasma chemical vapor deposition (ICPCVD) at $150\,^{\circ}\mathrm{C}$ for use in temperature-constrained superconducting detector fabrication. We measure the dielectric loss tangent of these films at $\sim 4-7$ GHz using superconducting niobium microstrip resonators and extract the loss by fitting the temperature-dependent resonant frequency to a two-level-system model. We vary the N$_2$/SiH$_4$ precursor-flow ratio between dielectric depositions and find a clear trend of decreasing loss with decreasing N$_2$/SiH$_4$. We additionally find that applying an RF substrate bias during deposition reduces the loss compared to films deposited without bias. These results identify precursor ratio and substrate bias as practical process parameters for improving low-temperature SiN$_x$ for superconducting detector circuits.
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All authors H. Athreya, J. Cornelison, M. Mikhailov, R.J.H. van der Kolk, C. Chang, T. Cecil, M. N. Ali, J. A. Zebrowski

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Impact of site-dependent noise configurations on Einstein Telescope science at low frequency

Francesco Crescimbeni, Matteo Di Giovanni, Davide Rozza et al. (+9 more)

We investigate how site-dependent Newtonian noise configurations affect the scientific performance of the Einstein Telescope (ET), a third-generation gravitational-wave observatory. We compare the baseline triangular and 2L detector geometries, with arm lengths of 10km and 15km, respectively, under three site-dependent noise scenarios constructed from measurements in the Euregio Meuse-Rhine region, Lausitz, and Sardinia. The differences among the adopted sensitivities are concentrated mainly below 10Hz and thus have the greatest impact on science cases that rely on the early inspiral of light objects, or on massive systems whose characteristic frequencies lie in the low-frequency band. We quantify these effects for four ET science cases: (1) detection and parameter estimation of intermediate-mass black-hole binaries; (2) post-Newtonian tests of General Relativity based on the early inspiral; (3) black-hole ringdown spectroscopy with massive remnants; and (4) early-warning and sky-localization capabilities for binary neutron-star mergers. Using Bayesian parameter estimation, we find that improved low-frequency sensitivity can significantly enhance ET's scientific performance across all four cases. Within the configurations considered here, a 2L network in which at least one of the two L-shaped interferometers attains a noise level comparable to that assumed for the Sardinian site generally provides better performance than the triangular configurations. Conversely, strong degradation of the sensitivity below 10Hz can substantially reduce, and in some regimes offset, the scientific gains expected from increasing the arm length from 10km to 15km. These results highlight the importance of site selection and low-frequency noise mitigation, alongside network geometry, for fully realizing ET's scientific potential in the largely unexplored frequency band below 10Hz.
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All authors Francesco Crescimbeni, Matteo Di Giovanni, Davide Rozza, Andrea Contu, Alessandro Cardini, Domenico D'Urso, Carlo Giunchi, Luca Naticchioni, Marco Olivieri, Mike Lindner, Andreas Rietbrock, Paolo Pani

Instrumentation and Methods for Astrophysics

BOLT: Imaging Lightning and Terrestrial Gamma-ray Flashes at the Pierre Auger Observatory

Eric-Teunis de Boone for the Pierre Auger Collaboration

Lightning-related phenomena are known to interact with and influence all detector systems of the Pierre Auger Observatory. Notably, the Surface Detector has recorded unique signals associated with Terrestrial Gamma-ray Flashes (TGFs), which are rare phenomena linked to the initial processes of lightning. Studying TGFs in coincidence with their parent lightning discharges helps to constrain the mechanisms responsible for their production, providing key insights into how these high-energy emissions are generated and evolve within thunderstorms. To image the parent lightning discharges, we are developing the Broadband Observatory of Lightning and TGFs (BOLT), an interferometric lightning mapping array that enhances the unique capabilities of the Observatory by providing high-resolution 3D (spatial and temporal) imaging of lightning propagation. BOLT consists of VHF radio detectors that have been previously developed for the Auger Engineering Radio Array, sensitive in the 30 MHz to 80 MHz range. The array is co-located with the Surface Detector to enable direct correlation between lightning activity and candidate TGF signals at the Pierre Auger Observatory. The BOLT array is in commissioning, with successful station firmware modifications to acquire and stream multi-second waveforms.
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Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.HE

Deep Learning for Cherenkov Astronomy: Performance of GammaLearn on LST-1

G. Grolleron, C. Plard, M. Dell'aiera et al. (+5 more)

The Cherenkov Telescope Array Observatory (CTAO) marks the next generation of Imaging Atmospheric Cherenkov Telescopes (IACTs), offering a sensitivity improvement of up to a factor of 10 over current instruments. Its first prototype, the Large-Sized Telescope (LST-1), is already in operation at the Roque de los Muchachos Observatory in La Palma, Spain. Deep learning methods have shown significant promise in reconstructing key properties of incident particles, such as energy, arrival direction, and type, using simulated data. Unlike traditional approaches that rely on simplified image shape parameters, deep learning can exploit the full temporal and charge information of the recorded events, providing enhanced performance, particularly at low energies (~20 GeV) accessible by LST-1. This capability is especially valuable for observing distant extragalactic sources like Active Galactic Nuclei, which are key to probing fundamental physics and cosmology. In this work, by producing sensitivity curves, we evaluate the performance of GammaLearn, a deep learning framework tailored for IACT data analysis, by comparing it to the standard analysis used with LST-1 and applying it to real observational data from LST-1.
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All authors G. Grolleron, C. Plard, M. Dell'aiera, T. François, V. Pollet, J. Talpaert, S. Caroff, T. Vuillaume on behalf of the CTAO-LST Project

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.SR

ROSE (Red-giant Oscillations Spectra Estimator): A Modular Machine-Learning Framework for Automated Asteroseismic Characterisation. I. $\nu_{\max}$ and $\Delta\nu$ from TESS

Nipun Ghanghas, Dinil B. Palakkatharappil, Rafael A. Garcia et al. (+1 more)

Space-based photometry from Kepler and TESS has delivered oscillation spectra for hundreds of thousands of red giants, and PLATO and the Roman Galactic Bulge Time-Domain Survey will add more. We present ROSE, a modular machine-learning framework for automated asteroseismic characterisation of red giants, and apply two of its modules to the frequency of maximum oscillation power, $\nu_{\rm max}$, and the large frequency separation, $\Delta\nu$. Each module is a neural network bundled with its own preprocessing transform and output binning, so that each parameter is measured in the representation that displays it most effectively: $\nu_{\rm max}$ from the power-density spectrum, and $\Delta\nu$ from the power spectrum of the power spectrum taken over a window centred on $\nu_{\rm max}$. Both are trained only on synthetic spectra generated at a one-year baseline and both return probability distributions rather than point estimates. This enables us to retrieve asymmetric uncertainty and a reliability index. Validating against held-out synthetic spectra, Kepler spectra at the training resolution and TESS continuous-viewing-zone giants, we obtain robust dispersions of 1.4, 3.3 and 4.4% in $\nu_{\rm max}$ and 0.35, 0.61 and 1.3% in $\Delta\nu$, with the $\nu_{\rm max}$ uncertainties close to their nominal coverage. The fully automated pipeline was applied to 274,721 TESS red-giant candidates observed for at least ten sectors, the framework returning reliable $\nu_{\rm max}$ for 56,224 stars and reliable $\Delta\nu$ for 39,939, taking 8 ms per star. The sample follows $\Delta\nu = 0.278 \nu_{\rm max}^{0.757}$ with a scatter of 6.2%, and the red-clump phase stands out as a distinct overdensity, although neither module is provided an evolutionary label or asked to produce one.
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All authors Nipun Ghanghas, Dinil B. Palakkatharappil, Rafael A. Garcia, Shravan Hanasoge

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.GA

IMFIT-MW: Multiwavelength photometric decomposition with IMFIT

Ilia V. Chugunov

Photometric decomposition is often used to study galaxy structure by modelling surface brightness distribution in its components. However, most of the relevant codes are designed for single-band analysis. I present IMFIT-MW: a lightweight, open source Python tool that extends IMFIT capabilities to simultaneously model multiwavelength images. IMFIT-MW is able to set shared parameters between filters and to impose smooth variation of them with wavelength. IMFIT-MW achieves this by using IMFIT to produce model brightness distributions for given parameters, whereas hyperparameters defining their wavelength dependence are fitted by an external optimizer. The code is available on GitHub (https://github.com/IVChugunov/IMFIT-MW). I provide a few examples of use, showing that IMFIT-MW matches GALFITM in single-thread performance and can have advantage of multithreading. In a broader sense, I demonstrate the possibility to extend IMFIT features even without modifying its source code.
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Instrumentation and Methods for Astrophysics

A Deep Learning Approach to Improving the Arrival-Direction Accuracy of Gamma-Ray Air-Shower Measurements with the Tibet-III Air-Shower Array

S. Okukawa, M. Kobayashi, K. Hara et al. (+8 more)

The Tibet AS$\gamma$ experiment observes cosmic gamma rays from several teraelectron volts to the petaelectron volt range using an array of ground-based surface air-shower detectors (Tibet-III), which is composed of plastic scintillators. The arrival direction is conventionally reconstructed by fitting the shower front to detector hit-timing data, and the resulting angular resolution is approximately 0.5$^\circ$ to 0.2$^\circ$ in the energy range from 10 to 100 TeV. In this study, to further improve the directional reconstruction accuracy, we developed a new arrival-direction reconstruction method that integrates a convolutional neural network (CNN) with the conventional method. Evaluations using gamma-ray events generated by Monte Carlo simulations show that the angular resolution is improved by approximately 10\,%–15\,% compared with that achieved with the conventional method. In addition, this performance improvement shows little dependence on the zenith angle up to 40$^\circ$. The proposed method provides a performance gain equivalent to increasing the Tibet-III array, which consists of approximately 600 detectors, by roughly 150 to 200 detectors.
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All authors S. Okukawa, M. Kobayashi, K. Hara, K. Hibino, Y. Katayose, K. Kawata, M. Ohnishi, T. K. Sako, T. Sako, A. Shiomi, M. Takita

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.GA

Registering Gaia positions on VLBI images: constraining opacity-driven core shift in B 1038+528 / B 1038+529

M. H. Xu and Y. Y. Kovalev

Because of the complex and time-variable radio structure of active galactic nuclei (AGNs), absolute astrometric positions cannot generally be registered unambiguously with specific features in VLBI images. We aim to register Gaia optical centroids on VLBI images with about 0.1 mas accuracy and to locate the optical emission relative to the radio core in the quasar pair B 1038+528 and B 1038+529, in which the opacity-driven core shift was first discovered. We combine the relative position of the pair from phase-referenced VLBI at four epochs between 1981 and 1995, their Gaia optical positions, and the nearly orthogonal radio-jet directions. Assuming that each Gaia–core displacement lies along the local jet axis, we register the Gaia centroids relative to the radio cores with about 0.1 mas accuracy without using absolute VLBI positions. The Gaia centroids lie upstream of the 8.4-GHz radio cores, by 293 {\pm} 93 {\mu}as in B 1038+529 and 169 {\pm} 96 {\mu}as in B 1038+528. The latter agrees with the 260 {\mu}as 8.4-GHz core shift implied by the 2.3–8.4 GHz shift measured for this quasar four decades ago. The absolute astrometric position of B 1038+528 with VLBI lies about 0.6 mas downstream of the core, and its geodetic position time series drifts along the jet by more than 1 mas, showing that the 0.8–1.6 mas Gaia–VLBI offsets of the pair are dominated by source structure rather than by core shift. Gaia positions can be registered on VLBI images with an accuracy set by the astrometry uncertainties. If the Gaia centroids mark the jet base, the measured separations are absolute 8.4-GHz core shifts, corresponding to projected distances of about 1.2 pc and about 2.5 pc from the jet base; a contribution from an optical jet emission would make them lower limits. The method is applicable to AGNs with Gaia detection and phase-referenced VLBI astrometry.
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Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.EP

A comparison between particle and fluid approaches for streaming instability in global patch simulations

Dominik Hetzel Ostertag, Mario Flock, Paul Rosendahl et al. (+3 more)

Identifying the process relevant to planet formation is still a major task. Mechanisms have been identified that can trap dust, preventing it from migrating inwards. A particular hydrodynamic instability, known as the streaming instability, is of high interest because it may be responsible for the formation of dust clumps from which the first planetesimals form. We aim to compare the outcome of non-linear streaming instability simulations using both fundamental approaches in a more realistic global disk model. The results will not be used to identify or disentangle the effect of, e.g., numerical diffusion in fluid simulations or the possibility of having crossing particle streams. Instead, they will enable us to determine whether the Lagrangian particle approach is the most suitable for numerical studies of the streaming instability. Methods: We perform 2D, axisymmetric, global, and isothermal hydrodynamic simulations using the two codes FARGO3D (dust fluid) and PLUTO (fluid, particles) to investigate the temporal evolution of dust scale height, midplane dust-to-gas ratio, and maximum dust density as well as to study velocity distributions and vorticities. For PLUTO particle simulations, we also investigate the influence of the gas Riemann solver and spatial reconstruction orders. Our results from a resolution study up to 5120 cells per gas scale height indicate convergence between PLUTO fluid and FARGO3D. Both yield a Gaussian profile dominated by small-scale, dust-depleted voids. Particle simulations with PLUTO have not yet converged, as a transient midplane dust component persists, indicating the need for even higher resolution or more particles. Using a more accurate Riemann solver or a higher-order spatial reconstruction scheme helps to bring the dust density profile closer to the converged structure.
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All authors Dominik Hetzel Ostertag, Mario Flock, Paul Rosendahl, Andrea Mignone, Jeonghoon Lim, Jacob B. Simon

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.SR

ASTRAL: A Framework for Optimal Placement and Emulation of Stellar Evolution Models

Trevor Gravely, Marko Ristić and Brandon Barker

Generating dense grids of detailed stellar evolution simulations is computationally prohibitive, as resolving progressively complex nucleosynthesis chains and dynamical timescales incurs a rapidly increasing computational cost that scales with dimensionality and resolution. Existing simulation grids are sparse, heterogeneous, and often cover disparate regions of parameter space, limiting (direct) systematic comparison and broader generalization to downstream science analyses. We present ASTRAL (Active Simulation Tuning and Regression for Astrophysical Libraries), a publicly available framework for optimal placement and emulation of stellar evolution models. The ASTRAL framework builds surrogate models that provide a continuous representation of the parameter space which is populated by sparse simulation grids. Furthermore, ASTRAL interpolates across the simulation parameter space (e.g. zero-age-main-sequence mass) to predict stellar properties of stars with associated uncertainty estimates for systems not explicitly simulated. We show that ASTRAL significantly outperforms uniform placement in constructing emulation-ready model libraries that capture both global and local variability in the output features. We showcase the performance of our framework in the context of a simple, one-dimensional MESA model. Finally, we examine how our methodology can inform downstream applications by analyzing our emulator's predictive confidence when applied to supernova simulations. We emphasize that, while developed for stellar evolution, the ASTRAL framework is directly extensible to other simulation-driven domains where model evaluations are expensive and parameter spaces are high-dimensional.
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Instrumentation and Methods for Astrophysics

The Fast Transient Foreground Fog of LSST

G. Megias Homar, S. R. Kulkarni, C. S. Lage et al. (+3 more)

Studies with 1-m class telescopes have now established that glints from satellites and space debris are the main obstacles to searches for sub-minute optical transients. Here, we report a study of this foreground using observations from the Legacy Survey of Space and Time (LSST) with the Simonyi 8.4-m telescope at the Vera C. Rubin Observatory. From 2,955 pairs of consecutive 30-s exposures, spanning 4,755 deg$^2$ of unique sky area and an area-time coverage of 472 deg$^2$ hr, we identified a population of faint, PSF-like, sub-minute events, including isolated events with no linear sequences of repeated flashes (tracklets) indicative of a tumbling satellite. We extended measurements of this population to the faintest magnitudes yet probed, finding a lower-bound to the occurrence rate of $(9.55 \pm 0.14) \times10^6\,$sky$^{-1}\,$day$^{-1}$ to $\sim23$ mag (median of $\sim22.3$ mag). The large aperture of the Simonyi 8.4-m telescope provides an additional discriminator: orbital debris in low-Earth orbit are sufficiently out of focus that they are filtered out. We find that, for a $1^{\prime\prime}$ PSF, unresolved events are constrained to distances beyond 1,732 km, and identify a previously unreported population of glints consistent with medium-Earth-orbit altitudes with estimated sizes of order $\sim1$-3 mm. We also report two isolated events observed along sight lines deep within the Earth's shadow, for which a sunlit-debris origin is disfavored. The scant evidence is consistent with an eclipsing binary and a stellar flare. The robust way forward for sub-minute transients is simultaneous observations of the same field by two (or more) widely separated telescopes. The resulting measurement of parallax will cleanly eliminate local (primarily orbital) debris, clarifying the nature of this transient foreground. This understanding will help astronomers probe truly celestial optical bursts.
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All authors G. Megias Homar, S. R. Kulkarni, C. S. Lage, J. A. Tyson, S. M. Kahn, F. A. Harrison

Instrumentation and Methods for Astrophysics

Constrained Diffusion for Data-Scarce Orbital Monte Carlo in Constellation Tasking

Omar Ramadan, Sam Siavoshian, Amir Kashif Saeed et al. (+3 more)

Constellation Monte Carlo results depend on the orbital population used to evaluate a tasking policy. With scarce reference trajectories, replay limits geometric diversity, while independent orbital-element jitter can violate physical constraints. We study constrained diffusion for orbital-population augmentation. A force-conditioned diffusion model learns a 13-dimensional orbital prior, recovering semimajor axis from perigee altitude and eccentricity; Basilisk propagates each sample under one of five force-model tiers. Using 800 reference trajectories, we compare diffusion with jittered bootstrap, per-tier Gaussian mixtures, and a conditional variational autoencoder, and evaluate distributional fidelity, support shift, classical astrodynamics diagnostics, and 4,000 paired GoDSAT-compatible campaigns. The largest diffusion model achieves held-out trajectory MMD of 0.0171 +/- 0.0239, similar to bootstrap (0.0170) and the mixture (0.0198), but samples farther from training priors (median nearest-training distance 2.7 versus 0.10 standardized units). All generators fail to match the shifted-blind population (classifier AUC 0.991-0.998). Endpoint-conditioned samples satisfy Lambert boundaries but have greater interior error than the matched Lambert reference (29.2 versus 5.7 km mean RMSE). Residual diffusion improves selected sparse forecasts and catalog-mode recall but does not outperform classical estimators on custody ranking. In a fixed 16-satellite configuration, diffusion yields similar mean custody to replay and bootstrap, while the force-tier mixture shifts custody by about 5.5 percentage points. Constrained diffusion supports local, in-support augmentation but cannot replace orbital dynamics or serve as an operational posterior. Orbital-population construction is a consequential source of uncertainty in constellation analysis.
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All authors Omar Ramadan, Sam Siavoshian, Amir Kashif Saeed, Benjamin A. Johnson, Amin M. E.-A. Diab, Benjamin M. Rodriguez

Tuesday 6 October

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.HE

An All-Sky Search for Moving Gamma-Ray Sources with Fermi-LAT

Dou Lai and James Unwin

Nearby compact gamma-ray sources can move appreciably during the Fermi-LAT mission and thus evade searches that assume a stationary sky. Compact dark matter halos, dark matter spikes around primordial black holes (PBH), and evaporating PBH provide potential examples. We perform a novel all-sky search for steady point sources moving at 0.25 deg/yr-0.8deg/yr in ten years of 1-100 GeV Fermi-LAT data. For a transverse speed of 200 km/s, this angular range probes distances of roughly $3.0\times10^3$ AU to $9.7\times10^3$ AU. We find 577 candidate tracks, consistent with $533\pm27.0$ tracks in time-scrambled skies. We place a model-independent 90% upper limit of 80.8 recovered signal tracks. At peak calibrated sensitivity, this corresponds to fewer than 123 steady, full-sky sources with an incident $E^{-2}$ photon spectrum. We give the calibrated detection efficiency of the search to steady point sources and use it to derive illustrative constraints on both evaporating PBHs and PBHs surrounded by annihilating dark matter halos.
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Instrumentation and Methods for Astrophysics

Assessment of sky brightness in central Portugal: the Dark Sky destination "Aldeias do Xisto" case study

Domingos Barbosa, Dalmiro Maia, Bruno Morgado et al. (+5 more)

A combination of remote sensing techniques, open space data and field testing was developed to derive astronomical and meteorological parameters and assess Dark Sky brightness of the hitherto unstudied Schist Villages region in the mountainous Interior Center of Portugal. This study covered the period 2012-2017 and established the methodology for regular light pollution and sky brightness studies in the region using satellite imagery to reduce cost and time and increase accuracy of the final analysis. Long-term Artificial Light At Night (ALAN) data from VIIRS instrument aboard the Suomi-NPP satellite along with cloud cover inferred from MODUS/AQUA satellite data and orographic data, were analyzed in a Geographical Information Systems (GIS) environment. The derived ALAN values were consistent with a preliminary site survey selection, confirming the accuracy of the identified dark sky spots in the region. The analyzed region area spans 1624 Km$^2$ and the darkest site within it showed a sky brightness of 21.4 mag/arcsec$^2$. Ground-based SQM photometer observations of the Night Sky Brightness (NSB) at the zenith validated the satellite derived ALAN data. The devised field testing is itself a low cost solution that can be used by teams in developing countries to easily assess dark sky potential prior to the development of local observatories and astro-tourism activities. This study supported the initial certification of this region as a Dark Sky Starlight Tourist Destination since 2018, an important milestone for dark sky protection in central Portugal.
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All authors Domingos Barbosa, Dalmiro Maia, Bruno Morgado, Pedro Cruz, Bernardo Relvas, Valério Ribeiro, Allan Kardec de Almeida Jr., Timothée Vaillant

Instrumentation and Methods for Astrophysics

A method for multimodal analysis of TAIGA experiment data using essential features

Alexander Kryukov, Julia Dubenskaya, Elena Fedotova et al. (+6 more)

The aim of processing and analyzing experimental data from physical experiments is to obtain physically significant information about the phenomenon under study. This goal is achieved by multi-stage processing of experimental data, during which noise associated with measurements is suppressed and the dimensionality of the input data is reduced. In this paper, we propose a new method based on the use of neural networks such as autoencoders to extract essential features. The special value of the proposed approach lies in the possibility of its application to the analysis of multimodal data received simultaneously from several installations. We will apply this approach to a multimodal data (MMD) of the experiment TAIGA. Currently, the analysis of the MMD is carried out independently for each installation separately. Therefore, the development of methods for the joint analysis of MMD from TAIGA-type installations is an urgent task in cosmic ray physics and gamma-ray astronomy. Based on Monte Carlo simulation, it is shown that the proposed method allows for effective MMD analysis. It can also be used for MMD analysis at other experimental complexes.
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All authors Alexander Kryukov, Julia Dubenskaya, Elena Fedotova, Elizaveta Gres, Stanislav Polyakov, Eugene Postnikov, Alexander Razumov, Pavel Volchugov, Dmitry Zhurov

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.GA

Modeling the nanohertz gravitational wave background with the t-process: Improved frequentist analysis of gravitational-wave power

B. E. Moreschi, K. A. Gersbach, G. Shaifullah et al. (+2 more)

Pulsar timing array (PTA) collaborations have recently reported evidence for a gravitational wave background (GWB) signal in the nanohertz band, which most likely originates from the incoherent superposition of GWs emitted by a population of supermassive black hole binaries (SMBHBs). Since the number of binaries emitting in each frequency bin is finite, and since individual loud sources can dominate the GWB, the power spectral density (PSD) of the background is expected to deviate significantly from the smooth power law that describes an idealized population. PTA searches usually describe the PSD either with a power law or with a free spectrum model, which fits the PSD in each frequency bin as a free parameter. In this paper, we explore the t-process as a third model; it assumes a power law as the underlying spectrum but leaves each frequency bin free to deviate from it. We compare the performance of these three models on simulated datasets, injecting $100$ realizations of a realistic SMBHB population, to evaluate how well each model recovers a complex PSD. Using Bayesian and frequentist tools, we find that the t-process model gives the most precise PSD results, with uncertainties $43\%$ and $26\%$ narrower than those obtained with the power law and the free spectrum, respectively, while the improvement in accuracy is smaller. Moreover, using the t-process model, we compute isotropic and anisotropic signal-to-noise ratios with median gains of about $46\%$ over the power law and $65\%$ over the free spectrum in the first nine frequency bins. The t-process also returns lower anisotropy p-values and among the frequency bins with $p<0.01$, it allows to localize the loudest binary within the angular resolution of the sky maps in $14.3\%$ of the cases, compared to the $10\%$ for the power law and the $6.2\%$ for the free spectrum.
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All authors B. E. Moreschi, K. A. Gersbach, G. Shaifullah, S. R. Taylor, A. Sesana

Instrumentation and Methods for Astrophysics

Space-based Cosmic Neutrino Measurements

John F. Krizmanic

Space-based neutrino detection employs celestial bodies, the Earth, moon, and the sun, as neutrino targets and particle cascade generators. These cascades, or showers, have an immense content of charged particles, mainly electrons and positrons, that can form signals that can be detected by orbiting or balloon-borne (for the Earth) experiments. Here the focus will be on the using the Earth as the neutrino target and using the atmosphere to generate optical and radio signals from extensive air showers (EAS). Cascades in the Earth itself can also generate Askaryan radiation in ice, where the radio transparency allows the signal from in ice neutrino-induced showers to eventually refract out of the Earth's surface. These different techniques also have different neutrino-flavor detection sensitivities and duty cycles, i.e. experimental live time fractions. For example, optical measurements need to be performed close to astronomical night and are also affected by the level of moonlight and distribution of clouds in the the viewing direction of the EAS. The radio technique can be operate with nearly 100% efficiency, as long as sources of anthropogenic and other backgrounds are minimal. Given the distances for viewing the neutrino-induced signals from sub-orbital or low Earth orbit (LEO) altitudes, the neutrino energy thresholds for detection are currently above $\sim$ 1 PeV for optical Cherenkov detection and 100 PeV for radio detection. In this chapter, the nature of the cosmic neutrino interactions, shower development, and optical and radio signal generation and detection will be detailed. This will be done by discussing experiments that have used such signals to set limits on the very-high and ultra-high energy cosmic neutrino flux. We will also discuss the design and simulated performance of the next generation of space-based cosmic neutrino detection experiments.
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Instrumentation and Methods for Astrophysics

Nancy Grace Roman Space Telescope Wide Field Instrument: Grism Saturation Response to Bright Sources during Thermal-Vacuum Testing

Lipika Chatur, Dana R. Louie, Joshua E. Schlieder et al. (+3 more)

The Nancy Grace Roman Space Telescope launched on August 30th, 2026 and is expected to begin its science mission in 2027. Although Roman's core science will focus primarily on faint and distant sources, as a survey telescope, it will also observe many bright sources that can saturate the detector pixels. Our goal is to study the behavior caused by bright sources dispersed through the grism and to assess how detector properties may impact scientific analysis. We analyze detector saturation behavior in Roman's Wide Field Instrument (WFI) using Thermal Vacuum Test 2 (TVAC2) bright-source grism data. When bright sources are dispersed through the grism, we find that the faint and diffuse combined orders cause significant structured stray light. We also find that pixels neighboring saturated pixels continue to exhibit linear growth behavior before reaching saturation limits, in contrast to the non-linearity reported for non-dispersed bright point sources.
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All authors Lipika Chatur, Dana R. Louie, Joshua E. Schlieder, Robert F. Wilson, Evan Bray, Scott Rohrbach

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.EP

Reflex instabilities II: The reflex motion of the central object drives at least seven instabilities in accretion discs

Nathan Magnan, Michel Tagger, Clément Baruteau et al. (+3 more)

This series of papers studies the stability of accretion discs to the reflex motion of the central object under the gravitational pull of the disc itself. In this second paper, we use linear analysis to reproduce or discover seven distinct instabilities. We outline their defining characteristics and propose a classification. Of the four instabilities that had already been discovered, three are artificial: one does not survive the transition to modern surface density profiles such as power-laws, one is due to the location of the domain's boundaries, and one is due to the use of damping layers near the domain's boundaries. Only the SLING instability of Adams et al. (1989) and the three new 'cavity' instabilities seem capable of affecting accretion discs. All four can be described to a high degree of precision by WKB methods. They may drive eccentricity growth, affect planet migration, create spiral and crescent substructures in the absence of any planet, and boost accretion onto the central object. The issue is that the three artificial instabilities are extremely hard to avoid in simulations, and would bias the same observables. This suggests that our community may not have the tools to model the reflex motion of the central object yet.
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All authors Nathan Magnan, Michel Tagger, Clément Baruteau, Aurélien Crida, Jean-François Gonzalez, Héloïse Méheut

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.EP

Reflex instabilities I: Boundaries makes grid-based disc simulations frame-dependent

Nathan Magnan, Michel Tagger, Clément Baruteau et al. (+3 more)

If the mass distribution within an accretion disc is asymmetric, it will exert a gravitational pull on its central object. The central object must then move away from the origin of the reference frame, resulting in atypical gravitational pulls on the disc. The goal of the present series of papers is to investigate the stability of this feedback loop. In this first paper, we report a surprising finding: the choice of reference frame affects the number and nature of the waves and instabilities contained in the analytical equations. To show this, we use a simple example: the modes discovered by Sanchez et al. (2025, Appendix A.3). We provide the first analytical description of those modes, we explain their physical mechanism, and propose to call them 'bracket modes' because they arise from the bracket side of an integration by parts. We show that the same disc can be stable in the stellocentric reference frame but unstable in the barycentric reference frame. This is because the boundaries of the simulation domain are frame-dependent. To avoid this, one must model the entire disc all the way from the central cavity to the outer edge. But this is prohibitively expensive, and some discs do not have a central cavity anyway. Our results suggest that extreme caution is required when interpreting simulations of asymmetric discs, and that our community may not have the tools to model the reflex motion of the central object yet.
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All authors Nathan Magnan, Michel Tagger, Clément Baruteau, Aurélien Crida, Jean-François Gonzalez, Héloïse Méheut

Instrumentation and Methods for Astrophysics

Rapid Sequence Cost Evaluation for Multi-Spacecraft Rendezvous: A Permutation-Invariant Set Transformer

An-yi Huang

Multi-spacecraft multi-rendezvous mission design requires repeated evaluations of the total cost of visiting a target set within a given time window, and the efficiency of this evaluation is the primary barrier to global search. Existing methods either optimize the order and epochs of each candidate sequence, which is expensive, or estimate the cost leg by leg, in which case the error accumulates with the sequence length. This paper proposes a deep model that regresses the total cost of an unordered target set directly: the pairwise transfer cost surface of each target pair is compressed into a latent feature, and a permutation-invariant transformer encoder regresses the sequence cost from these features and the window parameters, without ordering information. Trained on about 0.85 million labeled sequences, the model attains a mean relative error near 5% and a sub-millisecond evaluation time, about five orders of magnitude faster than precise optimization. Embedded into an evolutionary global search and applied to the GTOC9 problem, it yields the best known solution at every fleet size considered, from seven to ten spacecraft: directly, it produces near-optimal solutions cheaply, and as the initial guess of a differential-evolution refinement it improves the best published solutions further. The evaluator is not specific to this problem or to debris removal: it requires only a pairwise transfer cost function and a sequence-level cost metric monotone in the leg costs, and therefore applies equally to the servicing of satellites in low Earth orbit and to multi-target visits in deep space.
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Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.EP

Blinding Lights: Simulation-Based Evidence for Terrestrial Giant Impacts as Astronomically Observable Events

Lucy Taylor, Simon J. Lock, Philip J. Carter et al. (+1 more)

Giant impacts (collisions between planet-sized bodies) are violent events that fundamentally alter the properties of planets and the structure of planetary systems. Observations of these events provide important constraints on the role of giant impacts in the formation of planetary systems. However, relating such observations to the specifics of the impact responsible is challenging, since numerical simulations struggle to resolve the expected extreme low densities of observable material at the edge of ongoing impact structures. In particular, lower limits on density are often enforced in SPH codes for computational efficiency. Here, we present a method of post-processing output from smoothed particle hydrodynamics (SPH) simulations of giant impacts, that emulates realistic physical properties in multi-phase and multi-material collisions, in order to better understand these low-density outer regions. We apply our novel post-processing pipeline to determine the direct thermal emission and potential observational signatures of giant impacts, and obtain consistent photic surface geometries for an example impact simulated for a range of resolutions and code parameters. We find that during the first days after this terrestrial giant impact event, the emission from hot, unbound ejecta can be comparable in temperature and luminosity to that of an M-Dwarf star, and as such can be astronomically observable. Our work begins to bridge the gap between observations and theoretical models, and could allow high cadence, large-sky surveys, such as that to be carried out by the Vera C. Rubin Observatory, to place constraints on the frequency and properties of giant impacts in our local neighbourhood.
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All authors Lucy Taylor, Simon J. Lock, Philip J. Carter, Zoë M. Leinhardt

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.SR

Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) II. Approach to data reduction and products for line-rich broadband (sub)millimeter spectra

Adele L. Plunkett, Sébastien Maret, Daniel Harsono et al. (+26 more)

Studying the chemical composition of the warm gas surrounding embedded solar-type protostars is one of the areas for which the Atacama Large Millimeter/submillimeter Array (ALMA) is particularly well suited. Recently, the ALMA Large Program “Complex Organic Molecules in Protostars with ALMA Spectral Surveys” (COMPASS) carried out an observing campaign of a sample of 11 protostellar regions to investigate the chemical impact of their environments and evolutionary stages. The aim of this paper is to provide the observational and procedural information necessary for the community to understand the analysis presented in forthcoming scientific papers by the COMPASS collaboration, and to enable archival research using the data products provided by our team and the ALMA Science Archive. This paper describes the technical setup of the observations, and it outlines the data-processing pipeline and primary data products from this initiative. The Common Astronomy Software Applications (CASA) was used for initial calibration following the standard ALMA Pipeline, and then IMAGER was used for self-calibration and imaging. We describe post-processing done with Python to achieve favorable continuum subtraction, correct for the primary beam response, and extract spectra. We discuss our strategy for mitigating data challenges, including those related to data volume and continuum subtraction for spectral line analysis. The incorporation of IMAGER in our workflow was advantageous in terms of the computing efficiency which allowed us to benchmark several imaging parameters and techniques; we also demonstrate that the imaging outcomes using IMAGER or CASA are scientifically comparable. Numerous data products are generated for the program, including image cubes for the 36 spectral windows targeting each source, extracted spectra, and continuum images.
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All authors Adele L. Plunkett, Sébastien Maret, Daniel Harsono, Jes K. Jørgensen, Audrey Coutens, Maria N. Drozdovskaya, Jeong-Eun Lee, Arnaud Belloche, Fernando Cruz-Sáenz de Miera, Merel L. R. van 't Hoff, Jae-Hong Jeong, Chul-Hwan Kim, Ágnes Kóspál, Martine Lützen, Brett A. McGuire, Pooneh Nazari, Silvia Spezzano, Zoie Telkamp, Yao-Lun Yang, Hyeong-Sik Yun, Audrey Andreu, Jennifer Bergner, Judit Ferrer Asensio, Niels F. W. Ligterink, Yuxin Lin, Sheng-Yuan Liu, Pierre Marchand, Mihika Rao, Shaoshan Zeng

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.EP

Ariel Tier 3 Observations: An Opportunity to Explore both Stellar and Planetary Variability through Broad Wavelength Time-domain Spectroscopy

Alexandra H. Thompson, Quentin Changeat, Theresa Luftinger et al. (+1 more)

Ariel's Tier 3 observing strategy offers a unique opportunity to explore planetary and stellar variability in the spectral and time domain. However, without the correct toolkit, temporal variability of the host star may complicate combined analysesof observations obtained at different epochs. We investigate the impact of stellar variability on Ariel Tier 3 observations and establish three different mitigation approaches of increasing physical complexity. Using simulated repeated observations of a favourable system contaminated by different spot and facula configurations, we compare a naive, unmodified stacking approach, separate analysis of the infrared region through progressive removal of the most strongly contaminated optical wavelengths, and the correction of individual visits using combined star-planet retrievals. We find that stacking inconsistent visits can produce substantial biases in the retrieved planetary properties under strong stellar variability, although a single activity correction can still recover the planetary parameters reasonably well. Applying progressive optical data cuts substantially improves the accuracy of retrievals up to a point, without requiring any in-retrieval correction and causing only a modest loss of precision. Correcting individual visits prior to stacking produces more consistent spectra and generally smaller uncertainties, but requires greater computational effort. These results demonstrate that stellar variability should be considered when interpreting repeated Ariel observations, but need not preclude atmospheric characterisation of active systems. A flexible suite of mitigation approaches, supported by preparatory and contemporaneous stellar monitoring, can allow the treatment of stellar variability to be adapted to individual targets while maintaining the efficiency required to maximise Ariel's scientific return.
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All authors Alexandra H. Thompson, Quentin Changeat, Theresa Luftinger, Giovanna Tinetti

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Time-Frequency Analysis for LISA: Galactic Foreground Modulation

Sudhi Mathur and Neil J. Cornish

Observations by the Laser Interferometer Space Antenna (LISA) will contain time-varying, cyclostationary confusion noise from the Galaxy, which is naturally handled using time-frequency analysis methods. We present a fast, forward model that maps the parameterized Galactic gravitational-wave luminosity density onto the annually modulated, unresolved confusion foreground in the complete set of time-delay interferometry channels. The line-of-sight luminosity integral is evaluated on a HEALPix grid and decomposed into spherical harmonics, while the detector response is decomposed analytically, independent of the Galaxy model, such that a new Galactic model costs a single map evaluation, transformation, and contraction. We compute the modulated covariance beyond the standard low-frequency limit, expanding the LISA response to second order in finite armlength corrections, and to first order in the unequal-arm corrections. These effects change the normalized modulation curves by up to $\sim\!0.23\%$ and $0.64\%$ for finite armlength corrections at $3$ and $5$ mHz respectively, and by $\sim\!0.074\%$ and $0.71\%$ for unequal-arm corrections in the self and cross channels respectively. Using the fast, forward model and a notional disk-and-bulge Galaxy model, we construct a Fisher matrix from the time-dependent channel covariance and forecast that one year of observation constrains the disk scale width and scale height relative to the distance to the Galactic center at the $8\%$ and $12\%$ levels respectively, and leaves the strongly correlated bulge fraction and bulge radius individually unconstrained.
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