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Physics Astrophysics Instrumentation and Methods for Astrophysics

astro-ph.IM Watch Instrumentation and Methods for Astrophysics

Saturday 10 October

Instrumentation and Methods for Astrophysics

From Sky to Science: Time Domain Astronomy with the ILMT Survey

Kuntal Misra, Bhavya Ailawadhi, Talat Akhunov et al. (+10 more)

The PyLMT transient detection pipeline has been operational since November 2023 and has detected $\sim$10,000 transients and variable objects in ILMT images in near real time. The survey has enabled the discovery and characterisation of a range of bright and faint optical transients. The detected population spans a broad diversity of astrophysical phenomena, including supernovae, variable stars, active galactic nuclei (AGN) variability, and Solar System objects such as asteroids and comets. We provide a concise overview of the detection of a variety of transient and variable classes identified with the ILMT, emphasising the survey's potential contributions to a broad class of astrophysical sources. We highlight representative science cases, including supernovae, AGNs, variable stars, and asteroids, to demonstrate the scientific potential of the ILMT survey.
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All authors Kuntal Misra, Bhavya Ailawadhi, Talat Akhunov, Monalisa Dubey, Naveen Dukiya, Sara Filali, Paul Hickson, Priyanshi Kumari, Gokul Singh Mehra, Vibhore Negi, Kumar Pranshu, Jean Surdej, Sarvesh Kumar Yadav

Instrumentation and Methods for Astrophysics

Modelling the Point Spread Function of ILMT images

Naveen Dukiya, Bhavya Ailawadhi, Talat Akhunov et al. (+11 more)

We have devised an approach to model the empirical Point Spread Function (PSF) of the images taken with the 4-meter International Liquid Mirror Telescope (ILMT). The characteristics of the ILMT PSF are influenced by the nature of the Liquid Mirror, as well as by instrument specific and atmospheric factors. As the telescope uses Time Delay Integration (TDI) mode for tracking the passing objects, the PSF varies along the declination axis due to differential motion and star-trail curvature. The 5-element optical corrector homogenizes the PSF to some degree, but does not completely eliminate the disturbing effects mentioned above. The PSF in the RA direction is changing due to the sky conditions. We show that we can successfully model the PSF of 4k$\times$4k chunks using PSFEx, accounting for second-order X-Y variability. Our software robustly reproduces the PSF and its variation across the field.
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All authors Naveen Dukiya, Bhavya Ailawadhi, Talat Akhunov, Monalisa Dubey, Sara Filali, Paul Hickson, Priyanshi Kumari, Gokul Singh Mehra, Kuntal Misra, Vibhore Negi, Kumar Pranshu, Jean Surdej, Sarvesh Kumar Yadav, Archana Gupta

Instrumentation and Methods for Astrophysics

Mid-IR Water-Vapor Seeing: Implications for ELT/METIS High-Contrast Imaging from VLTI Data

Abhirami S Raghu, Prashant Pathak, Olivier Absil et al. (+7 more)

Direct imaging and characterization of rocky exoplanets remains one of the central challenges in exoplanetary science. The mid-infrared (mid-IR) offers a favorable high-contrast imaging (HCI) regime, as the planet-star contrast is more moderate than at shorter wavelengths. However, mid-IR observations with extremely large ground-based telescopes (ELTs) are strongly affected by spatio-temporal fluctuations in atmospheric water vapor (WV), which introduce chromatic wavefront errors that are largely invisible to adaptive optics systems operating at shorter wavelengths. This poses a significant challenge for mid-IR HCI instruments such as METIS, which aims to detect thermal emission from rocky exoplanets in the $N$-band (8–13 $\mu$ m). To quantify WV-induced wavefront errors, we analyze $K$-band fringe-tracker data from the GRAVITY instrument at the VLTI and derive the optical path difference between group-delay and phase-delay measurements. This difference provides a direct measure of the differential WV column density ($\Sigma$) above the telescopes. We examine the dependence of the RMS differential WV column density ($\sigma_{\Sigma}$) on precipitable water vapor (PWV), airmass, seeing, and wind speed across multiple VLTI configurations. Among these parameters, PWV shows the strongest correlation with $\sigma_{\Sigma}$. We further explore the influence of the vertical PWV distribution on this relationship. Next, we use power-spectral-density analysis to quantify how increasing PWV modulates $\Sigma$ variability. The wavefront error associated with this phenomenon on ELT scale is approximately 15~nm RMS in the $L$-band and 175~nm RMS in the $N$-band, relative to the $K$-band. These results provide a quantitative framework for assessing and mitigating atmospheric WV effects in next-generation mid-IR HCI instruments.
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All authors Abhirami S Raghu, Prashant Pathak, Olivier Absil, Benjamin Courtney-Barrer, Gilles Orban de Xivry, Julien Woillez, Alexis Matter, Philippe Bério, Roy van Boekel, Bernhard Brandl

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

Milani and Juventas Optical Navigation Images in Support of the Hera Radio Science Experiment

Edoardo Gramigna, Ozgur Karatekin, Birgit Ritter et al. (+7 more)

The European Space Agency's Hera mission aims to advance planetary defense by investigating the Didymos binary asteroid system following NASA's DART impact on Dimorphos. Incorporating simulated CubeSat images into Hera's orbit determination framework significantly improves positional accuracy, reducing uncertainties by up to three orders of magnitude for Milani and one for Juventas. This data enable more precise estimation of key parameters such as asteroid masses, rotational states, and moments of inertia, with up to 90% uncertainty reduction in Dimorphos' dynamical state under chaotic scenarios. Sensitivity analysis reveals the influence of pointing accuracy, image noise, and imaging frequency. Additionally, dedicated scientific investigations using Dimorphos-focused CubeSat images further advance understanding of the system. These findings underscore the critical role of CubeSat images in refining navigation and advancing science, offering valuable insights for future small-body missions.
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All authors Edoardo Gramigna, Ozgur Karatekin, Birgit Ritter, Iosto Fodde, Fabio Ferrari, Felice Piccolo, Paolo Tortora, Riccardo Lasagni Manghi, Marco Zannoni, Ryan S. Park

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

Hera Orbit Determination Covariance Analysis of Didymos Binary Asteroid with the Full Two-Body Problem

Edoardo Gramigna, Riccardo Lasagni Manghi, Marco Zannoni et al. (+7 more)

Standard planetary radio science analyses may be inadequate for accurately interpreting data from the Hera mission at the Didymos system due to the anticipated challenge posed by the coupling between the translational and rotational motions of the asteroids. A more precise dynamical model, the full two-body problem model, which includes a mutual gravitational potential, may be required to fit the Hera data properly. This work presents a covariance analysis of the Hera radio science experiment using this advanced model. The tested dynamical scenarios are based on recent lightcurve observations indicating that Dimorphos is in an excited non-principal axis spin state that is, on average, tidally locked. Three non-principal axis scenarios are analyzed using a multi-arc local estimation approach instead of the global one adopted in previous investigations involving non-chaotic states. The results show that tumbling or chaotic cases significantly improve the recovery of the bodies' moments of inertia due to the enhanced observability of the system's dynamics from the excited spin state. However, the local estimation approach slightly degrades the accuracy of the mass estimation by a factor of 1.3-3 and Dimorphos' relative orbit by about one order of magnitude. Developing a dedicated constrained multi-arc filter is thus required to improve the estimation accuracy of the Didymos system's dynamical state further. Nevertheless, these results still meet the Hera radio science requirements.
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All authors Edoardo Gramigna, Riccardo Lasagni Manghi, Marco Zannoni, Paolo Tortora, Michalis Gaitanas, Ioannis Gkolias, Kleomenis Tsiganis, Ryan S. Park, Alex Meyer, Petr Pravec

Instrumentation and Methods for Astrophysics

ELISA: A Bayesian X/$\gamma$-ray Spectral Analysis Toolkit

Wang-Chen Xue, Sheng-Lun Xie, Chao Zheng et al. (+11 more)

Forward-folded X/$\gamma$-ray spectral fitting increasingly benefits from Bayesian workflows to better capture counting statistics, background uncertainties, and complex parameter degeneracies, while fully reproducible end-to-end implementations are still not always straightforward to deploy in routine analyses. We present ELISA (Efficient Library for Spectral Analysis), an open-source Python toolkit that streamlines the full spectral analysis loop for X/$\gamma$-ray astronomy: data loading, model construction, inference, and model validation and comparison. ELISA couples a JAX-accelerated forward model with a unified fitting interface, supporting both rapid optimization and modern Bayesian sampling. Built-in diagnostics make convergence checks and predictive assessment a standard part of the workflow, motivating principled model refinement when needed. Using a spectral fitting example of the Insight-HXMT Crab observation, we find substantial improvements in sampling efficiency compared with XSPEC's default MCMC implementation. ELISA is available at https://github.com/wcxve/elisa and on PyPI at https://pypi.org/project/astro-elisa.
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All authors Wang-Chen Xue, Sheng-Lun Xie, Chao Zheng, Shao-Lin Xiong, Xiao-Bo Li, Yong Chen, Peng Zhang, Yan-Qiu Zhang, Jia-Cong Liu, Chen-Wei Wang, Wen-Jun Tan, Yue Wang, Jin-Peng Zhang, Zheng-Hang Yu

Friday 9 October

Instrumentation and Methods for Astrophysics

Harmonic and intermodulation emission from direct-to-device satellites - Harmonics of the Starlink 2.6 GHz downlink and the products around them

Balthasar Indermuehle, Benjamin Winkel, Federico Di Vruno et al. (+2 more)

Direct-to-device (DTD) satellites carry mobile base stations transmitting in terrestrial mobile bands. Their non-linear emission products can fall into radio astronomy bands, including passive bands. We measure the harmonics of the Starlink DTD downlink at 2620-2630 MHz and the intermodulation products around them, search for products next to the carriers, and compare them with the ITU-R unwanted-emission limits and radio astronomy protection criteria. We use autocorrelations of single Australia Telescope Compact Array antennas on tracked passes of DTD and other satellites with the 16 cm and 4 cm receivers. Harmonic ratios and receiver tests show that the harmonics are satellite-generated. We simulate the aggregate equivalent power flux density of a constellation at Effelsberg and the ATCA. The harmonics H2 to H4 at 5240, 7860 and 10480 MHz fall by about 16 dB per order, show no trend with elevation, and originate on the satellite. H2 is also detected in 32% of integrations more than 10 degrees from any DTD satellite. Inside the harmonic zones the spectra follow the n-fold convolution of the carriers; outside them, intermodulation products of order n+2 and higher lie on average 19 dB below the zone and switch between -23 and -15 dB within seconds. Next to the carriers no satellite emission is detected to 33 dB below the carriers. H2, >=-38.9 dBW in 4 kHz isotropic-equivalent, is at or above the SM.329 space-station limit; H3 and H4 meet it. For 8640 satellites the aggregate exceeds the protection criteria by 65 and 25 dB at the second and fifth harmonics, and by >100 dB for out-of-band emission at the mask level in 2690-2700 MHz. Harmonics are received far outside the serving beams. Their radiated level must be limited directly, not through the power at the antenna port. Compliance with per-satellite ITU-R limits does not protect radio astronomy from the aggregate of a constellation.
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All authors Balthasar Indermuehle, Benjamin Winkel, Federico Di Vruno, Gyula Jozsa, Liroy Lourenco

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

What does self-supervision add to engineered features for stellar light curves?

Zijun Liu, Yue Ma and Christopher A. Theissen

TESS light curves encode a star's pulsation, rotation, binarity and oscillations, among other physical properties, but the survey produces far more light curves than can be labelled by hand. Astronomers have engineered a few dozen physically motivated features from them, which together remain a strong baseline. Previous work has trained encoders on light curves and judged them by their own downstream scores, but has not asked what they add to the engineered features. We pre-train a convolutional encoder on unlabelled TESS light curves to predict each window's latent representation from those of its neighbours. We then freeze it, add its features to the 25 engineered features, and read the combination out with one fixed linear probe on ten tasks: five variability classes, four asteroseismic targets and rotation period. Adding the learned features improves the readout on 7 of 10 tasks over the engineered features alone, where an untrained encoder does not. The combination also outperforms two networks trained end-to-end on the same labelled stars on most tasks. An encoder trained without labels therefore gives astronomers new features that complement the ones they already use rather than replace them.
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Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.HE

A Pipeline for the AI-Assisted Analysis of Imaging X-ray Polarimetry Explorer Observations of Black Hole X-ray Binaries and Limits on Their Polarization Variability

B. Domine, B. Liu, H. Krawczynski et al. (+3 more)

The Imaging X-ray Polarimetry Explorer (IXPE) has opened a new window into the high-energy Universe, with the capability to measure the arrival time, arrival direction, energy, and, for the first time with the required sensitivity, the polarization of X-rays from black holes, neutron stars, and other cosmic sources of X-rays. In this paper, we discuss the use of Artificial Intelligence (AI) agents for the analysis of IXPE data. The pipeline combines an immutable code base with evolving knowledge databases. The generation of analysis projects makes use of a literature data base to judge the novelty of the proposed analysis projects. We emphasize that the analysis requires two types of expert knowledge: detailed instructions about how to reduce the X-ray data, and expert knowledge about how to interpret the results. We employ several levels of auditors that scrutinize the analysis plan, the analysis scripts, and the analysis results for data and method adequacy. The pipeline includes a staggered approach to interpret the analysis results. We present exemplary results from the pipeline applied to IXPE observations of Black Hole X-ray Binaries (BHXRBs) including comparisons of results from the analysis pipeline with published results and a systematic search for polarization degree and polarization angle variability in long IXPE observations. We critically discuss the performance of the pipeline and future avenues for improving it.
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All authors B. Domine, B. Liu, H. Krawczynski, M. Kundu, Shravan Vengalil Menon, Fang Zhou

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

Stellar discs and intermediate-mass black holes in galactic nuclei II. Fragmenting the disc and forming the S-stars in a live nuclear star cluster

Taras Panamarev and Bence Kocsis

We present direct $N$-body simulations of a stellar disc around the supermassive black hole Sgr~A*, perturbed by an intermediate-mass black hole (IMBH) and embedded in a live nuclear star cluster. A retrograde IMBH with $m_\bullet=2000\,M_\odot$, relative inclination $\theta_\bullet=150^\circ$, and initial semi-major axis $a_\bullet=0.15$~pc breaks the disc into three disc-like components and an angular momentum filament. The stochastic torques of the cluster, together with the IMBH's inward migration, increase the angular separation between these substructures. By ${\sim}5$~Myr, their separations become comparable to those among the observed Galactic-centre young star structures. The innermost ($a\le0.04$~pc) disc stars evolve into an S-star-like population. Relaxation driven by the cluster disperses their orbital planes, excites their eccentricities and depletes the `zone of avoidance' within ${\sim}10$~Myr even without an IMBH. The IMBH further accelerates their orbital-plane reorientation. However, the most eccentric S-stars may require an additional formation channel, such as the Hills mechanism. The distinctive signatures of the IMBH are the well-separated disc components and the eccentricity excitation confined to the radial range swept by its orbit. Dynamical friction from the cluster reduces the orbital size of a $2000\,M_\odot$ IMBH initially at $0.15$~pc by more than a factor of two within $10$~Myr. Prograde IMBHs tend to align with the stellar disc, whereas a $2000\,M_\odot$ retrograde IMBH can anti-align with the radially overlapping disc stars. We also quantify how the IMBH affects the supply of stars to the loss cone and the rates of stellar tidal disruptions and binary separations.
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Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.EP

Assessing PLATO's Discovery Potential across Different Observing Strategies

Yoshi Nike Emilia Eschen, Michelle Kunimoto, Juan Cabrera et al. (+11 more)

The PLATO mission, planned to launch in spring 2027, will observe a fixed Southern field, LOPS2, for at least 2 years with the goal of discovering and deriving precise parameters for planets as small as Earth around FGK dwarfs and sub-giants. Afterwards, PLATO could continue to monitor the same field or move to a Northern field, LOPN1, overlapping with the Kepler field. We assess these two observing strategies in terms of sensitivity of detecting small and long period planets, and subsequently we estimate yields for both observing strategies. Within this we account for including the Kepler data in the LOPN1 field, monitoring of up to 8 years of the LOPS2 field, and the sensitivity improvement from combining TESS and PLATO data since both fields have been and will be continued to be observed with TESS. We find that by monitoring both fields, and hence more stars, the total number of newly discovered planets is maximised. However, to optimise the number of discovered small and long periods planets, long-term monitoring of one field produces the best results. The combination of Kepler and PLATO data improves detection sensitivities; however, as this only covers a fraction of the LOPN1 field and stellar sample, it improves the yields of small and long period planets only marginally. Hence, to detect and characterise small and long period planets in this sparsely explored exoplanet parameter space, a longer continuous observation of the LOPS2 field is best.
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All authors Yoshi Nike Emilia Eschen, Michelle Kunimoto, Juan Cabrera, Adrien Leleu, Thomas G. Wilson, Heike Rauer, Alex Romanec, François Bouchy, Magali Deleuil, Nicholas Jannsen, Don Pollacco, Toby Rodel, Sophia Sulis, Stéphane Udry

Instrumentation and Methods for Astrophysics

First Experimental Results of Space Object Detection Using the InteRFeX Array

Bhaskar Ahuja, Thomas Crowther, Steven Tingay et al. (+3 more)

This paper presents the first experimental validation of InteRFeX, a non-uniform receive only (passive) array located at the Nova Systems Space Precinct in Peterborough, Australia, designed for space domain awareness applications. It operates over a frequency range of 70 to 300 MHz and is capable of functioning in a range of observational modes, including as a coherent passive bistatic radar for space surveillance, which is the focus of this work. InteRFeX exploits commercial broadcast transmissions as illuminators of opportunity, combining cross-ambiguity function processing for bistatic range and range-rate retrieval with MUSIC-based direction-of-arrival (DoA) estimation for angular localization. The International Space Station (ISS) serves as the experimental target, with measurements evaluated against Two-Line Element (TLE) orbit predictions. Taking advantage of the dual-polarized array, all four reference–surveillance polarization combinations are evaluated, revealing differences in detection rate and mean signal-to-noise ratio (SNR) over the observation pass, with bistatic-range RMSEs of approximately 1 km relative to the TLE-derived reference. Independently, the MUSIC-based DoA estimates exhibit a mean angular separation of approximately $0.45^\circ$ from the TLE-derived reference directions. The angular deviations are further decomposed into along-track and cross-track components, enabling a more detailed characterization of the DoA offsets relative to the TLE-derived reference trajectory. The processing framework also includes a first-order bistatic link-budget analysis to estimate the expected SNR over the observation geometry. These results demonstrate the feasibility of passive-radar space domain awareness using radio-interferometric array technology and establish the proposed signal-processing pipeline as a basis for a dedicated coherent passive-radar mode within InteRFeX.
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All authors Bhaskar Ahuja, Thomas Crowther, Steven Tingay, Andrew Guidi, Luca Gentile, Marco Martorella

Instrumentation and Methods for Astrophysics

An empirical calibration of the spectral resolution of JWST NIRSpec PRISM

Hang Zhou, Xin Wang, Yuxuan Pang et al. (+4 more)

We present an empirical calibration of the effective spectral resolution of the JWST NIRSpec PRISM disperser based on a large sample of galaxies drawn from archival observations. Our sample spans a wide redshift range, $0.5 \lesssim z \lesssim 10$, enabling a wavelength-dependent characterization of the PRISM resolving power across the full bandpass using the [O III]$\lambda\lambda4959,5007$ doublets. To ensure robust measurements, we impose strict signal-to-noise requirements on both continuum and emission-line detections. Emission-line profiles are fitted with multi-Gaussian models, and the full width at half maximum (FWHM) is measured for each source. The derived empirical resolution curve shows a systematic offset from the nominal pre-launch estimate, lying between the tabulated instrumental resolution and the point-source shutter limit. We also discuss how source size affects the final spectral resolution, and provide an analytical formula that combines wavelength and morphology dependence in a root-sum-square framework. This work delivers a population-averaged, statistically robust calibration of the effective PRISM spectral resolution for typical galaxy observations. The resulting calibration is directly applicable to statistical analyses of galaxy spectra obtained with NIRSpec PRISM. Our empirical calibration exceeds the pre-launch JDox values by a factor of 1.03 to 1.63, depending on source morphology, and provides the first wavelength and morphology dependent calibration of the NIRSpec PRISM spectral resolution.
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All authors Hang Zhou, Xin Wang, Yuxuan Pang, Shengzhe Wang, Karl Glazebrook, Themiya Nanayakkara, Hu Zhan

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

Combination of multi-observatory photometry to determine asteroid rotation periods

Kristers Nagainis and Ilgmars Eglitis

This study aims to determine asteroid rotation periods from sparse, unevenly sampled, multi-observatory photometry using the Lomb-Scargle (L-S) method. The photometric measurements of the asteroids are taken from the circulars of the Minor Planet Center (MPC). Twelve asteroids, four of them with known rotation periods, were analyzed with two complementary methods. In the separate dataset analysis (S-method), each observatory dataset was analyzed separately, and the final period was obtained as a weighted average of the consistent candidate periods, with weights based on the peak power of the power spectrum, the number of measurements, and the quality of the corresponding light curve fit. In the combined dataset analysis (C-method), all measurements were corrected for the biases of the photometric band, the star catalog and the observatory, reduced to a common scale and merged into a single dataset, after which the period was derived directly from the L-S analysis of the combined time series. Both methods produced consistent results, and they reproduced the known periods of the four test asteroids within 0.05%. The results show that the L-S method is well suited for finding rotation periods in sparse observations with uneven sampling over long time intervals. New rotation periods were found for asteroids 2968, 2971, 3081, 3473, 3716, and 4303. The period of 2968 remains ambiguous because of daily aliasing. For 3716, the most likely period is 10.474 hours, but its daily alias at 13.405 hours cannot be excluded completely. For 3173, the strongest peaks at 22.99 and 45.98 hours are probably daily aliases of a slower brightness variation. For asteroid 2607, the period agrees with a recently published value and is more precise. The approach is therefore promising for automated searches for unknown asteroid rotation periods.
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Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.HE

Simulation Study of Reconstruction of Cosmic Ray Extensive Air Shower with Thermal Neutron Detected by ENDA

Fan-Ping Li, Xin-Hua Ma, Hu Liu et al. (+25 more)

In the investigation of the "knee" region within the cosmic ray energy spectrum, extensive air shower (EAS) reconstruction by using different EAS secondary particles are of paramount importance for energy determination and composition separation and finally measurement of energy spectrum of different cosmic ray composition. The Electron-Neutron Detector Array (ENDA) is designed to detect thermal neutrons generated in the ground by high energy hadrons which constitute the "backbone" of EAS and carry vital information regarding the primary cosmic rays. At present, ENDA-64, consisting of 64 detectors, is employed inside the Large High Altitude Air Shower Observatory (LHAASO). This work simulates the response of ENDA and investigates the lateral distributions of thermal neutrons. A comparison of the NKG and double-exponential functions for describing this distribution using MC simulation data shows that the double-exponential function is more accurate. The mean difference between fitted and measured thermal neutron density is within ~ 6%. Meanwhile, the thermal neutron density at 10 m from the shower axis, $\rho_n$, depends mainly on the sum of all hadrons energy or the number of high-energy hadrons. The relationship between $\rho_n$ and EAS hadron energy or the number of high-energy hadrons can be well fitted by a linear function on a log scale. This work is fundamental for energy determination and composition separation with hybrid detection by using ENDA in the near future.
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All authors Fan-Ping Li, Xin-Hua Ma, Hu Liu, Tian-Lu Chen, Shu-Wang Cui, Danzengluobu, Xin-Rui Gao, Wei Gao, Wen-Chao Gao, Hai-Bing Hu, Denis Kuleshov, Kirill Kurinov, Bing-Bing Li, Mao-Yuan Liu, Ye Liu, Igor Maliy, Da-Yu Peng, Yao-Hui Qi, Jia-Bo Qin, Dong Qu, Oleg Shchegolev, Yuri Stenkin, Yu-Sen Wang, Tian-Shuang Yang, Li-Qiao Yin, Hui-Qian Zhang, Liang-Wei Zhang, Shi-Yuan Zhang

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

ASKAP Monitoring of the Rubin Deep Drilling Fields

Dougal Dobie, James Freeburn, Iris de Ruiter et al. (+5 more)

In the past decade, time domain astronomy surveys across the multi-messenger spectrum have developed "alert streams" which circulate observational information in real-time to the wider astronomical community. Despite this being standard practice for optical, gamma-ray and gravitational wave time domain astronomy for several years now, this kind of infrastructure has not yet been deployed at-scale for radio telescopes. We are conducting a long-term monitoring program that targets the Rubin Deep Drilling Fields using the Australian SKA Pathfinder (ASKAP). The primary goal of this program is to provide serendipitous radio observations of all objects of interest in these fields, and circulate that information in as close to real-time as possible. In this manuscript we outline the survey plans and status, the infrastructure we have developed to disseminate this information and an initial data release comprising 5 months of ASKAP observations of each field (although only 3 months overlaps with Rubin) conducted on an approximately 10 day cadence with a noise level of $\sim 60\,\mu$Jy. As part of this data release, we present updated high-cadence radio light curves to the tidal disruption event AT2018hyz and the supernova SN2024abfo along with the discovery of two new radio variables, a possible tidal disruption event ASKAP J095711.5+051205 and an in-progress extreme scattering event ASKAP J005026.4-422958. The scientific results from this program along with the infrastructure developed to acquire them will lay the foundation for the integration of future radio imaging surveys into the broader multi-messenger alert stream, leading the way for major facilities such as the Schmidt Observatory System and the SKA.
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All authors Dougal Dobie, James Freeburn, Iris de Ruiter, Katie Auchettl, James Coulson, Brent Miszalski, Anais Möller, Nikhil Sarin

Instrumentation and Methods for Astrophysics

An Ultraviolet Instrument on the Habitable Worlds Observatory: Considerations and Capability Trades on the Multi-Object, Integral-field, and High-resolution modes of a potential UVI

Brian Fleming, Kevin France, Dmitry Vorobiev et al. (+4 more)

The Habitable Worlds Observatory (HWO) is NASA's next-generation astrophysics platform, delivering transformative capability in the search for life and study of the origins of the universe. Amongst the instruments under consideration for HWO is a multi-purpose ultraviolet spectrograph and imager that provides a deep toolbox for some of the most pressing science investigations of the next several decades. In this paper, we present a basic draft model of a potential UVI, including a multi-object spectrograph, far ultraviolet imager, high resolution spectrograph, and integral-field spectrograph. The draft designs for these channels of the UV instrument serve as a basis for a general discussion of the instrument architecture and design challenges, while also identifying potential trades, enhancements, and other considerations that the HWO project will need to address as it moves into the formulation phase. We conclude with a presentation of several scientific simulations that have helped guide the capabilities of the draft design. This paper is intended to serve as a summary of UV instrument modes, technology, and potential design ahead of planned instrument studies in the late 2020's, and then Phase A in the early 2030's.
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All authors Brian Fleming, Kevin France, Dmitry Vorobiev, Jeanette Donber, Eric Frater, Thomas Delker, Vicki Herde

Instrumentation and Methods for Astrophysics

In-flight Timing Calibration of the Follow-up X-Ray Telescope on Board the Einstein Probe

Juan Zhang, Xiaofan Zhao, Dawei Han et al. (+18 more)

After the launch of Einstein Probe (EP), pulsars are observed to calibrate the timing system of the onboard Follow-up X-ray Telescope (FXT) by measuring the times of arrival (TOAs). FXT has two independently operating modules, namely FXTA and FXTB, each equipped with the Wolter-I optics and the pnCCD camera. For scientific observations, each pnCCD has three distinct readout modes that differ in frame cycles, the full frame mode (FF, 50 ms per frame), the partial windowed mode (PW, 2.2 ms per frame), and the timing mode (TM, 23.68 $\mu$s per row, 9.4352 ms per frame). Thus, 1RXS J170849.0–400910 with the spin period of 11 s is observed in FF, PSR B1509–58 (150 ms) in PW, and Crab pulsar (33 ms) in TM as well as PSR B1821–24 (3.05 ms) and PSR B1937+21 (1.56 ms). The TOAs of these pulsars measured by FXTA and FXTB are compared with the results of NICER, and for Crab pulsar with the Jodrell Bank Monthly Ephemeris (JBE). Results verify that the timing system of FXTA and FXTB in FF, PW, and TM modes are consistent with each other, and are in good alignment with NICER. The measured advance of the Crab pulsar's main peak relative to JBE is $357^{\pm14(stat)}_{\pm54(sys)} \mu$s in FXTA and $394^{\pm14(stat)}_{\pm67(sys)} \mu$s in FXTB. Based on measurements of PSR B1821–24 and PSR B1937+21, the preliminary absolute timing accuracy is estimated to be 6 $\mu$s for FXTA and 31 $\mu$s for FXTB in TM mode. Additionally, the systematic delay of FXTA timing results relative to FXTB is found to be $20^{\pm19(stat)}_{\pm21(sys)} \mu$s.
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All authors Juan Zhang, Xiaofan Zhao, Dawei Han, Hao Wang, Yong Chen, Mingyu Ge, Shijie Zheng, Shumei Jia, Haisheng Zhao, Weiwei Cui, Hanlong Peng, Wentao Ye, Yaoming Duan, Youli Tuo, Zhen Ji, Fuli Ma, Chengkui Li, Ju Guan, Jingjing Xu, Jin Wang, Liming Song

Thursday 8 October

Instrumentation and Methods for Astrophysics · Cross-listed from physics.optics

Phantom Zernike Wavefront Sensor: Phase Contrast with Engineered Focal Plane Reference Speckles

Benjamin Courtney-Barrer

We introduce the Phantom Zernike Wavefront Sensor (phantom ZWFS), an engineered reference extension of phase-contrast wavefront sensing in which controlled pupil plane modulation generates off-axis coherent speckle structures that undergo localized focal plane phase shifts. These references may replace the central ZWFS reference when the on-axis PSF core is required for another optical function, such as photonic science coupling, or may augment a conventional central ZWFS response to provide additional wavefront information. Using a monochromatic scalar model, we derive the resulting carrier structure and show how the engineered references can be recovered through spatial demodulation and incorporated into calibrated reconstruction. A simple four-reference realization demonstrates that the reference geometry redistributes photon sensitivity across spatial frequency magnitude and orientation, producing mode dependent changes in linearity and cross-talk rather than a uniform improvement over a classical ZWFS. We then consider differential piston on a seven segment aperture as an application specific example. A hybrid sensor retaining the central ZWFS phase region and adding six engineered references that match the segment geometry gives similar precision near the phased state but substantially improved performance at larger piston excursions. Under the adopted photon-noise-limited benchmark, the hybrid reduces the nonlinear reconstruction error and provides better conditioned optical encoding of the piston state than an idealized vector ZWFS, allowing more precise piston estimation from the same detected photon flux at larger piston excursions.
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Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.EP

The Fast & Fourier: Using neural operators to speed up radiative modeling of protoplanetary disks

Lukas Welzel and Melissa K. McClure

Edge-on protoplanetary disks provide a spatially resolved view of the vertical distribution of icy planetary building blocks, but inferring their relative abundances requires radiative-transfer (RT) modeling with multiple anisotropic scattering. Each model costs $10^{1}$-$10^{3}$ CPU hours, which precludes principled Bayesian inference and homogeneous, population-scale analyses. We develop and validate a fast and reusable surrogate for Bayesian inference with ice-bearing edge-on disk models. We train a Fourier Neural Operator on a grid of RADMC-3D spectra. The network maps disk parameters and analytic physical input fields to the spectrum, using mixed-resolution spectra. We use the surrogate in an explicit-likelihood nested sampler and validate it on held-out simulations and synthetic recovery tests with TARP coverage. Finally, we use it to retrieve the disk structure and ice abundances of ESO-H$\alpha$ 569 from its spectral energy distribution. The surrogate reproduces the RADMC-3D spectra with a median error of 4.84%. We recover synthetic parameters without detectable bias and with nominal coverage. For ESO-H$\alpha$ 569, the posterior favors a massive ($M_{\rm gas}=0.028^{+0.015}_{-0.011}\,M_\odot$), nearly edge-on ($i=79.8^{+5.2}_{-2.4}$ deg) disk consistent with the image-plus-SED model of Wolff et al. (2017). Its ice abundances and cavity size remain weakly constrained by broadband data alone. The marginal spectrum-evaluation speed-up is $\sim10^{9}$-$10^{10}$. Neural-operator emulation makes full posterior inference feasible within the adopted model and training prior. Key posterior points should still be checked with high-fidelity RT models. By drastically cutting evaluation time, this approach enables for the first time homogeneous population studies of ices in disks, which new JWST surveys can capitalize on to map the range of compositions within planetary nurseries.
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Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.EP

"Mega-Earths" are likely an artifact of stellar activity

Casey L. Brinkman and Nicolas Cowan

Empirical relations and planet formation simulations suggest an upper mass limit for rocky planets of $\sim$10M$_{\oplus}$, as cores above this will almost certainly undergo runaway gas accretion. Nevertheless, a small number of planets appear to have densities consistent with rocky Earth-like compositions above this threshold, indicating that unusual formation and evolutionary scenarios are capable of producing extremely massive rocky planets called "Mega-Earths." However, all of these planets orbit active stars with log$R'_{HK}$ $>$-4.75. We find a <1$\%$ probability that all literature ultra-massive rocky planets would coincidentally orbit such active stars, and find no astrophysical reason to expect Mega-Earths to preferentially form around active stars. We therefore conclude that Mega-Earths are artifacts of stellar activity, and we question the reliability of Gaussian Processes to enable mass measurements for rocky planets around active stars.
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Instrumentation and Methods for Astrophysics

Data Representation Matters: Optimizing Machine Learning for X-ray Source Classification by Leveraging Spatio-Spectral Information

Maggie Lieu, Ivan Valtchanov, Marguerite Pierre et al. (+4 more)

Distinguishing between faint extended X-ray sources is a fundamental yet challenging task in X-ray surveys. This paper presents a benchmark comparison of convolutional neural network models for classifying simulated XMM-Newton observations of AGN and galaxy clusters, focusing on the impact of data representation and interpretability of that data. We evaluate 1D, 2D, 2D+1D, and 3D CNNs trained on distinct data representations derived from simulated XMM-Newton observations of AGN and clusters: 1D (spectral), 2D (imaging) and 3D (event cube) data. We further apply 3D-GradCAM to interpret the learned features and assess the physical basis for the model's decision making to move beyond black-box classification. Our results demonstrate that increased spectral resolution enhances classifier performance using 1D and 2D information provides a strong baseline, the integration of both domains yields significant diagnostic gains. We find that a 3D CNN architecture applied directly to spatio-spectral event cubes provides the most robust performance, with superior consistency across cross-validation folds. Interpretability analysis reveals that the 3D model autonomously learns to distinguish the diffuse thermal emission of the intracluster medium from the localized, non-thermal power-law signatures of AGN. It exploits multi-dimensional correlations that are lost in lower-dimensional projections. While the performance gain over combined 2D and 1D baselines is marginal, the 3D approach demonstrates an ability to perform implicit background characterisation. By operating directly on total photon counts within event cubes, this method bypasses the need for manual background subtraction and modelling, offering a consistent, streamlined, end-to-end pipeline for automated classification of X-ray sources in large-scale catalogues.
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All authors Maggie Lieu, Ivan Valtchanov, Marguerite Pierre, Esin Gulbahar, Elias Koulouridis, Iván Muñoz Rodríguez, Lucio Chiappetti

Instrumentation and Methods for Astrophysics

Opening the Black Box: What Neural Networks Learn from Pulsar Timing Array Data

James Alvey, Andrea Mitridate, Mauro Pieroni et al. (+1 more)

In recent years, simulation-based inference (SBI) methods have been proposed to address several data-analysis challenges faced by existing and planned gravitational-wave experiments. For example, SBI classification has recently been shown to significantly improve the prospects for detecting anisotropies in pulsar timing array (PTA) data. In this work, we use a simple toy model of a PTA to provide a more pedagogical explanation of how, and under which circumstances, SBI-based detection can improve on classical detection statistics for gravitational-wave background anisotropies.
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All authors James Alvey, Andrea Mitridate, Mauro Pieroni, Joseph D. Romano

Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det

Cavity Characterization for the Princeton Axion Search

Nate Otto, Jianyang Fu, Joelle-Marie Begin et al. (+4 more)

The Princeton Axion Search (PXS) targets the mass window $0.8\text{--}2.1~\mu\text{eV}$ (corresponding to frequencies $200\text{--}500~\text{MHz}$) at DFSZ sensitivity. The experiment, a haloscope, will use a cylindrical copper-plated aluminum cavity of $700~\text{mm}$ diameter and $1022~\text{mm}$ height, immersed in a $5~\text{T}$ solenoidal magnetic field. A $152~\text{mm}$ diameter tuning rod spanning the height of the cavity rotates to tune the primary mode resonance from $390\text{--}480~\text{MHz}$, the frequency range for initial operations. We deduce the electric and magnetic field mode patterns using a combination of dielectric and metallic bead perturbations on the empty cavity. The measured mode frequencies and the $\text{TM}_{010}$ field profile, as a function of tuning rod position, are in excellent agreement with simulations. We describe the effect of fabrication and assembly imperfections, including the bowing of end plates and tilt of the tuning rod. The welded seams and end-cap joints are demonstrated to not significantly degrade $Q$. We combine measurement and simulation to assess an uncertainty on form factor across the full tuning range. Our results validate PXS's cavity architecture and inform future searches for sub-$\mu\text{eV}$ axions, in which large-volume high-$Q$ structures are required to reach QCD sensitivity.
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All authors Nate Otto, Jianyang Fu, Joelle-Marie Begin, Saptarshi Chaudhuri, Roman Kolevatov, Lyman Page, Joe Wiedemann

Instrumentation and Methods for Astrophysics

On-chip filled array hyperspectral kinetic inductance detectors (FHYKID) for line intensity mapping

Emile Prêle, Martino Calvo, Usasi Chowdhury et al. (+3 more)

The next generation Line Intensity Mapping (LIM) experiments will require very high throughput instrumentation, and as a consequence high pixel counts focal planes. For the study of the [CII] line in the redshift range z=7-8, we develop a hyperspectral filled focal plane (FHYKID) operating in the range 210-235 GHz and with a spectral resolution reaching 120. The spectral filtering is achieved thanks to planar Slot Split Ring Resonators (SSRR) coupled to Lumped Element Kinetic Inductance Detectors (LEKID). This robust concept achieves, thanks to its simplicity, large quantum efficiency and is scalable, even with current readout electronics systems, to several tens of thousands beams on Sky. Our FHYKID will be one of the four channels of the NIKONA instrument, currently seeking funding and to be installed at the IRAM 30-meter telescope at Pico Veleta. Among the science goals, simultaneously mapping the local (galactic and nearby-galaxies) CO line and the cosmological [CII].
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All authors Emile Prêle, Martino Calvo, Usasi Chowdhury, Gregory Garde, Florence Levy-Bertrand, Alessandro Monfardini

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

Testing General Relativity with Binary Lens Microlensing Events

Xinyang Jin, Shuo Cao, Xuanni Chen et al. (+3 more)

Einstein's General Relativity (GR), which has been precisely tested on galaxy and solar system scales, is still poorly constrained in extremely weak gravitational fields (with dimensionless Newtonian potentials of $\Phi \sim 10^{-8}$). In this Letter, we propose a new method to probe such a weak-field regime of gravity and measure the spatial curvature generated per unit mass. Specifically, binary microlensing events provide a laboratory to measure the parameterized post-Newtonian (PPN) parameter ($\gamma$), by combining the lensing mass ($M_{\rm lens}^{\rm GR}$) inferred from microlensing with the dynamical mass ($M_{\rm dyn}$) determined from interferometric astrometry. Astrometric tracking of binary lenses was previously hindered by their faintness and minuscule angular separations (typically a few milliarcseconds). This limitation has been alleviated by the deployment of GRAVITY+, which pushes the instrument's sensitivity and astrometric precision to unprecedented heights. Based on astrometric simulations of the binary microlensing event ASASSN-22av, we directly estimate $\gamma$ at the precision of ~23%. Such test of GR in the extremely weak-field regime can be further improved to much higher precision (~3%), based on more binary microlensing events with precise determination of the dynamical/lens mass.
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All authors Xinyang Jin, Shuo Cao, Xuanni Chen, Yalong Nan, Xuchen Tai, Shuxun Tian

Instrumentation and Methods for Astrophysics

A Coherent Harmonic Summing Pulsar Search Code

Scott M. Ransom

Pulsars have narrow pulses, so their signals spread over many harmonics in a Fourier transform. Standard pulsar searches add the powers of those harmonics and discard their phases, which throws away the pulse shape and some of the signal. Folding the time series at each trial period keeps both, but is expensive even with the Fast Folding Algorithm (FFA). We describe CoherentSearch.jl, an open-source Julia code that reconstructs the pulse profile at every trial spin frequency directly from the Fourier transform. It interpolates the complex amplitudes of typically 60 harmonics, inverse transforms them into a profile, and tests that profile against boxcar templates of many widths. Because the input spectrum is normalized, the noise in every profile is known in closed form, so one threshold gives one false-alarm rate across the whole search. In an injection study of over 860,000 simulated pulsars at a matched false-alarm rate, the new search recovers 76% of the pulsars in white noise, against 64% for riptide's FFA in its recommended configuration and 42% for PRESTO's accelsearch, and its threshold does not move under red noise. On one CPU core it is 1.4-2.2 times faster than riptide at matched frequency coverage, it scales to 27 times faster on 48 cores, and modern GPUs run it up to nine times faster than a 20-core workstation.
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Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.EP

Gravitational Microlensing

Aikaterini Vandorou and Stela Ishitani Silva

Gravitational microlensing is a unique planet-detection method that does not rely on detecting light from the host star or planet. Instead, planets are discovered when their gravitational field perturbs the light coming from a distant source. The mechanics of this method offer several advantages. It has the ability to detect wide-orbit planets of various masses around host stars of different types, at and beyond the system's snow line. Thus, microlensing complements the other detecting techniques that are more sensitive to close-orbit or high-mass planets. In this Chapter, we review the microlensing method and discuss how the physical properties, such as mass and distance, can be extracted from the microlensing light curve or from additional high-angular resolution observations. Microlensing is essential for the broader context of exoplanet demographics, as it can place constraints on planets, in wide orbits, beyond the snow line. Studying this parameter space can help us unravel the details of planet formation and how our own Solar System formed. Lastly, we provide an example of how to model a light curve and obtain accurate physical parameters for the host and planet.
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Instrumentation and Methods for Astrophysics

Pseudo Closed-Loop Bootstrapping for Reinforcement Learning Based AO Control

Eemil Halonen, Jalo Nousiainen, Markus Kasper et al. (+1 more)

High contrast imaging with ground-based telescopes requires extremely precise wavefront control. The performance of the controller ultimately depends on the quality and efficiency of the wavefront sensing technique, which has led to the development of ever more sensitive wavefront sensors (WFS). However, the increase in sensitivity comes at the cost of greater nonlinearity, which poses challenges for conventional linear reconstructors and controllers. Reinforcement Learning (RL) is a branch of machine learning in which control policies are learned by interacting with the environment. RL has recently attracted interest in the field of XAO, and previous studies have demonstrated that a model-based RL variant, the Policy Optimization for Adaptive Optics (PO4AO), can effectively compensate for temporal delays, misregistration errors, and moderate WFS nonlinearities. PO4AO learns an initial control strategy by collecting closed-loop data from the integrator controller with a linear reconstructor. However, in cases of highly non-linear WFS and challenging conditions, closing the loop with the integrator is difficult, and high-fidelity data cannot be collected. Consequently, learning robust control with PO4AO is challenging. We propose a robust learning strategy in which PO4AO is pre-calibrated using an internal light source and a DM, enabling direct on-sky closed-loop operation without a stable integrator controller for bootstrapping the initial models.
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All authors Eemil Halonen, Jalo Nousiainen, Markus Kasper, Nuutti Hyvönen

Instrumentation and Methods for Astrophysics

radio-astro-tools: linking radio astronomical data to the astronomical Python ecosystem

Eric W. Koch, Adam Ginsburg, Thomas P. Robitaille et al. (+15 more)

We present the radio-astro-tools code suite, which consists of several Python packages that enable analysis of radio data, especially interferometric spectral cubes, in the context of the Astropy software ecosystem. While these tools were designed with radio data in mind, they are built to be general and have applications on data sets at other wavelengths. The core package, spectral-cube, handles reading, writing and analysis of cube data, and it enables straightforward parallelization via dask and joblib backends. Support packages include casa-formats-io and radio-beam, which handle reading of CASA tables & images and reading and manipulation of point spread functions, respectively. The pvextractor package facilitates creation of position-velocity diagrams. The uvcombine package implements the "feather" algorithm for combining single-dish and interferometric data. The development of radio-astro-tools included several contributions to other repositories, including matplotlib, astropy, and regions to support interaction between CASA and other parts of the astronomy software ecosystem. We also present a detailed set of tutorials written in Jupyter notebooks that can be run interactively in a browser, providing more accessible access to data analysis for radio spectral-line data cubes.
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All authors Eric W. Koch, Adam Ginsburg, Thomas P. Robitaille, Erik W. Rosolowsky, Alyssa Bulatek, Savannah Gramze, Jonathan D. Henshaw, Derek Homeier, Preshanth Jagannathan, Amanda A. Kepley, Adam K. Leroy, Sébastien Maret, Stuart Mumford, George Privon, Álvaro Sánchez-Monge, Srikrishna Sekhar, Brigitta Sipőcz, A.J.M. Thomson