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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 27 April

Cosmology and Nongalactic Astrophysics

Nonparametric Variational Inference Reconstruction of the Cosmic Expansion History from SNe Ia – the charm2 code

Iason Saganas, Matteo Guardiani, Natalia Porqueres et al. (+1 more)

Cosmological analyses using the latest set of type Ia SNe data weakly favor an evolving dark energy (EDE) model without strongly disfavoring the standard LCDM paradigm. Nonparametric reconstructions of the expansion history may reveal signal features potentially missed by a parametric LCDM model without laying out a specific functional form for the evolution of dark energy. Information field theory (IFT) is a Bayesian framework for optimal, nonparametric reconstruction algorithms. In this work, we present charm2, the successor to charm1, a previous IFT-based code to reconstruct the cosmic energy density's redshift evolution from SNe Ia. We apply our reconstruction algorithm to the Union2.1, Pantheon+, DESY5 and DESY5-Dovekie data sets to investigate the agreement between the nonparametric reconstruction and the signal suggested by a parametric, flat LCDM model. To enable an accurate Gaussian approximation, we employ geometric variational inference, which finds a coordinate transformation through which a curved posterior gets "flattened". The redshift evolution of the energy density can then be traced on a double-logarithmic scale, which, after de-trending, is well described by a stationary Gaussian process. The nonparametric charm2 reconstructions using the Union2.1 and Pantheon+ data sets are consistent with flat LCDM signal fields. The DESY5 and DESY5-Dovekie reconstructions deviate from flat LCDM comparison fields and are compatible with an evolving dark energy signal. However, using the evidence lower bound (ELBO) measure for model selection, we find no conclusive evidence supporting a preference for non-flat-LCDM features in any of the data sets. We note that at current DESY5 noise levels, the ELBO tends to favor flat LCDM over our nonparametric model although the latter better recovers the ground truth in synthetic EDE data; a trend reversing only at ~7x lower noise covariance.
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All authors Iason Saganas, Matteo Guardiani, Natalia Porqueres, Torsten Enßlin

High Energy Astrophysical Phenomena

Accurate distances of the Galactic spiral arms from dust-scattered X-ray emission of gamma-ray bursts

B. Vaia, I. Fornasiero, A. Tiengo et al. (+5 more)

The details of the spiral structure of the Milky Way are still debated due to large uncertainties in the distance estimates obtained through the most common tracers. X-ray dust scattering rings produced by short extragalactic X-ray transients provide instead a direct method to measure the 3D distribution of interstellar clouds up to the edges of our Galaxy with a few percent precision. We report on the analysis of all the available XMM-Newton and Chandra follow-up observations of three low-latitude gamma-ray bursts: GRB 031203 ($l \sim 255{\deg}$, $b \sim -5{\deg}$), GRB 160623A ($l \sim 84{\deg}$, $b \sim -3{\deg}$), and GRB 221009A ($l \sim 53{\deg}$, $b \sim 4{\deg}$). The previous detection of X-ray rings in these observations, produced by dust clouds located beyond 5 kpc, can be associated with dust in the Perseus, Outer, and Outer Scutum-Centaurus arms, thus providing direct distance measurements to these structures along three distinct lines of sight. We have identified two additional rings in the direction of GRB 160623A, produced by dusty clouds at $6.91\, \pm\,0.06$ kpc and $9.9\,\pm\,0.6$ kpc, and confirmed – through a second XMM-Newton observation – the presence of one cloud at $9.7\,\pm\,0.4$ kpc toward GRB 031203. We also accurately measured the distance of dusty clouds up to $19.0\,\pm\,0.2$ kpc owing to the analysis of one Chandra and four XMM-Newton observations of GRB 221009A. The small statistical and systematic uncertainties of these measurements place tight constraints on the geometry of the outer Milky Way and reveal significant deviations from current models, which critically depend on spectroscopy-based Galactic rotation curves at large distances.
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All authors B. Vaia, I. Fornasiero, A. Tiengo, A. Bracco, V. Jelić, Ž. Bošnjak, F. Pintore, P. Esposito

Earth and Planetary Astrophysics

Mars Thermospheric Polar Warming at Aphelion: Dynamical Processes Studied Using M-GITM

Jia-Zheng Li, Stephen W. Bougher, Cheng Li et al. (+1 more)

Aphelion Thermospheric Polar Warming (TPW), first identified in 2024 by Mars Atmosphere and Volatile EvolutioN (MAVEN) observations, is a dynamical heating phenomenon in the Martian atmosphere that exists in the winter hemisphere near the aphelion solstice. Studying the formation mechanism of aphelion TPW will help us better understand the energy budget of the Martian thermosphere. In this study, we investigate aphelion TPW using the Mars Global Ionosphere Thermosphere global circulation model (M-GITM). The simulation results show that the local dust storms have little impact on the formation of aphelion TPW. The simulated thermospheric temperature difference between the polar region and the low-latitude region is considerably lower than the value observed, which suggests that some important atmospheric processes are not captured by M-GITM. To investigate potential causes, we conduct sensitivity tests on solar insolation, gravity waves, and model horizontal resolution. The sensitivity test on solar insolation shows that the magnitude of aphelion TPW increases with increasing solar insolation. We also find that gravity waves play a critical role in modulating dynamical heating, as their suppression increases the latitudinal temperature difference. Model resolution has minimal impact on polar warming but affects thermospheric structure at low latitudes. These findings highlight the importance of refining the representation of dynamical processes, especially the parameterization of subgrid-scale internal gravity waves in the Martian general circulation model to better capture thermospheric dynamics.
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All authors Jia-Zheng Li, Stephen W. Bougher, Cheng Li, Erdal Yigit

Solar and Stellar Astrophysics

A Theoretical Study of the Structure and Elemental Abundances of HD 20794

Mrinmay Medhi, Mami Deka, Krishna Saha et al. (+2 more)

HD~20794 is a nearby, bright, metal-poor G-type dwarf hosting a compact planetary system, including a super-Earth near the habitable zone. Its low stellar activity and the availability of precise radial-velocity and photometric data make it an excellent benchmark for studying stellar structure and chemical abundances in low-metallicity planet-hosting stars. We present, to our knowledge, the first grid-based stellar evolution analysis of HD~20794 using MESA, focusing on its main-sequence and late main-sequence evolution. A set of 252 stellar models was computed for initial masses between $0.78$ and $0.80\,M_{\odot}$, varying convective efficiency, numerical resolution, and atmospheric boundary conditions. Models were selected through $\chi^2$ minimization using observed constraints on effective temperature, surface gravity, luminosity, radius, and age. The best-fit models favor a mass of $0.80\,M_{\odot}$ and an age of about $9$~Gyr, reproducing all observed stellar properties within uncertainties. They also successfully recover the observed surface abundance pattern over a wide range of elements, including light elements, $\alpha$-elements, and the odd-$Z$ species phosphorus and chlorine. Comparison with nucleosynthesis yields from massive stars suggests that the measured phosphorus and chlorine abundances are compatible with enrichment from core-collapse supernovae and have remained preserved during stellar evolution. Our results support standard stellar evolution theory, indicating that low-mass, metal-poor G dwarfs such as HD~20794 can retain their natal chemical signatures over Gyr timescales. This highlights their importance as probes of stellar evolution, Galactic chemical enrichment, and the chemical environments associated with long-lived planetary systems.
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All authors Mrinmay Medhi, Mami Deka, Krishna Saha, Vivek Baruah Thapa, Upakul Mahanta

Astrophysics of Galaxies · Cross-listed from cs.AI

A systematic evaluation of vision-language models for observational astronomical reasoning tasks

Wenke Ren, Hengxiao Guo, Wenwen Zuo et al. (+1 more)

Vision-language models (VLMs) are increasingly proposed as general-purpose tools for scientific data interpretation, yet their reliability on real astronomical observations across diverse modalities remains untested. We present AstroVLBench, a benchmark of over 4,100 expert-verified instances across five tasks spanning optical imaging, radio interferometry, multi-wavelength photometry, time-domain light curves, and optical spectroscopy. We systematically evaluate six state-of-the-art frontier models and find that performance is strongly modality-dependent and uncorrelated with general benchmark rankings. Mechanistic cross-model ablations reveal three concrete bottlenecks. First, prompt grounding exhibits marked model and task dependence: physical guidance yields more balanced classifications on optical imaging, whereas phenomenological prompts better navigate undersampled time-domain data. Second, presenting one-dimensional measurements as numerical tables rather than rendered plots consistently improves light-curve classification across all models by up to 23 percentage points, demonstrating that plot rendering can obscure physically relevant signal. Third, an expert audit of optical spectroscopy reveals a notable "right-answer-wrong-reason" phenomenon: across evaluated models, an average of 26% of correct predictions are accompanied by physically inconsistent or invalid reasoning chains, showing that accuracy alone is insufficient for trustworthy scientific deployment. AstroVLBench provides the first systematic, multi-modal baselines for VLMs in observational astronomy and identifies the representation, grounding, and reasoning bottlenecks that must be addressed before VLMs can be trusted as autonomous scientific interpreters.
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All authors Wenke Ren, Hengxiao Guo, Wenwen Zuo, Xiaoman Zhang

Astrophysics of Galaxies

Investigating interstellar dust along the line of sight of GX 13+1 using different dust size distributions

B. Vaia, S.T. Zeegers, I. Abril-Cabezas et al. (+1 more)

Context. High-resolution X-ray spectroscopy offers a powerful tool to investigate the physical and chemical properties of dust grains, especially through the analysis of absorption edges of elements such as oxygen, magnesium, silicon, and iron, which are the main constituents of interstellar dust. In all previous X-ray studies, these absorption edges have been modeled assuming the MRN grain size distribution. This model successfully reproduces the average interstellar extinction curve. However, with the advent of new observations, it shows important limitations, indicating that more complex grain-size distributions are required to fully describe interstellar dust properties. Aims. We aim to constrain the composition and size distribution of interstellar dust along the line of sight to the bright low-mass X-ray binary GX 13+1. Methods. We analyzed high-resolution X-ray spectra obtained with the Chandra HETG instrument (MEG+1 and MEG-3) and simultaneously modeled the Si K and Mg K absorption edges. For the first time, we compared the classical Mathis et al. 1977, ApJ, 217, 425 grain size distribution with other grain size distributions, thus exploring different ISM densities. Results. Our analysis rules out scenarios of both very diffuse and very dense ISM, favoring grain size distributions associated with average Galactic conditions along this line of sight. The dust composition is found to be dominated by amorphous olivine and the crystallinity contribution is about 2%. The depletion patterns and elemental abundances derived are consistent with prior X-ray and infrared studies.
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All authors B. Vaia, S.T. Zeegers, I. Abril-Cabezas, E. Costantini

Earth and Planetary Astrophysics

The spin state of asteroid Apophis and a prediction of its change during the 2029 close encounter with Earth

J. Durech, D. Vokrouhlicky, P. Pravec et al. (+23 more)

On April 13, 2029, the asteroid Apophis will pass near Earth at a geocentric distance of about 38,000 km. Numerical models have suggested that the post-encounter spin state will critically depend on the orientation of Apophis during the flyby. We aim to determine the spin state of Apophis from its photometric observations collected during two apparitions in 2012-2013 and 2020-2021. This will enable us to accurately predict the pre-encounter rotation state and, by accounting for Earth's gravitational torque, predict a range of possible post-encounter states. We used the light curve inversion method for tumbling asteroids to reconstruct the spin state of Apophis and its convex shape model. The result is adopted as the initial condition of a numerical model describing Apophis's future rotation state. The data from the two apparitions are insufficient to determine Apophis's rotation and precession periods uniquely. The formally best-fit solution is 27.374 +/- 0.001 h for the precession period and 262.2 +/- 0.1 h for the rotation period, but at least two other combinations of the periods provide a similarly good fit to the available data. All the currently acceptable models result in approximately the same pre-encounter orientation of Apophis in early 2029. This is because the accurate photometric data were collected during two apparitions separated by 8 years, which is the same interval as from 2021 to 2029. Although the close encounter with Earth in April 2029 hugely increases the post-encounter uncertainty of Apophis's spin state, the short-axis spin mode will be preserved with a high likelihood. Additional observations taken in 2027 and 2028 will break the ambiguity in Apophis's pre-encounter spin solution and allow us to get a more accurate post-encounter spin state prediction
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All authors J. Durech, D. Vokrouhlicky, P. Pravec, K. Hornoch, P. Kusnirak, P. Fatka, H. Kucakova, J. Hanus, M. Ferrais, E. Jehin, Z. Benkhaldoun, O. Humes, D. Polishook, M. Marsset, G. McMillan, E. Podlewska-Gaca, M. Colazo, A. Marciniak, K. Kaminski, M. K. Kaminska, S. Zola, M. Drozdz, W. Ogloza, M. Zejmo, B. Carry, D. E. Reichart

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Tests of scalar polarizations with multi-messenger events

Sk Md Adil Imam and Macarena Lagos

Gravitational wave (GW) observations provide a unique opportunity to test Einstein's General Relativity (GR) in the strong-field regime. While GR predicts only two tensor polarization modes, generic metric theories allow up to six independent modes. We perform a parameterized test of GR using the parameterized post-Einsteinian (PPE) framework applied to GW170817, incorporating for the first time the polarization angle constraints from the gamma-ray burst afterglow alongside other electromagnetic (EM) counterpart information. We extend the GR waveform by adding a scalar breathing mode and modifications to the tensor modes, introducing three non-GR parameters. We perform Bayesian inference for both quadrupole $\ell = |m|= 2$ and dipole $\ell = |m|= 1$ angular harmonics, with two frequency evolution models. For $\ell = |m| = 2$, we find that within the extended PPE framework the scalar amplitude deviates from zero at the $2$–$3\sigma$ level, leading to a modest preference for modified gravity. However, due to penalization of extra parameters, Bayesian model comparison still favors pure GR over the extended PPE waveform model, with a log Bayes factor of $\Delta \log \mathcal{Z} = 4.67 \pm 0.32$. The EM constraint on the polarization angle places very tight bounds on non-GR parameters; for instance, in the case $\ell = |m| = 2$, the bound on the scalar (tensor) amplitude modification parameter improves by roughly $60\%$ $(30\%)$, highlighting the impact that long-term follow up of GW events can have on tests of gravity.
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Solar and Stellar Astrophysics

StarCLR: Contrastive Learning Representation for Astronomical Light Curves

Junyao Ding, Xiaodian Chen, Xinyi Gao et al. (+7 more)

With the rapid development of time-domain surveys, the availability of massive light curve data offers new opportunities for studying stellar evolution and variable star classification, while simultaneously posing challenges for feature extraction and modeling. We present StarCLR, a contrastive pretraining framework for large-scale light curves. By constructing positive pairs from partially overlapping sub-sequences, StarCLR encourages the model to learn temporal representations. We pretrain StarCLR on the TESS dataset and fine-tune it for variable star classification on three surveys with distinct observational characteristics, namely TESS (18 types), ZTF (11 types), and Gaia (24 types). StarCLR achieves macro-F1 scores of 84.35%, 87.82%, and 92.73%, and micro-F1 scores of 94.46%, 92.83%, and 99.49%, respectively. Compared with LSTM and Transformer trained from scratch, StarCLR performs better on TESS and ZTF, with the largest gains on sparsely sampled ZTF light curves, demonstrating promising generalization. For Gaia, which involves a broader class space, the evaluation is not directly comparable, and performance is likely influenced by astrophysical features, resulting in a more limited contribution from the pretrained backbone. Systematic ablations on embedding design, pooling strategy, and pretraining settings further indicate that the pretrained representations provide performance gains by capturing informative temporal characteristics of light curves. Looking ahead, with standardized datasets and more diverse labeling schemes, the generalization ability of StarCLR can be further enhanced.
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All authors Junyao Ding, Xiaodian Chen, Xinyi Gao, Xiaoyu Tang, Shu Wang, Yang Huang, Xinyu Qi, Guirong Xue, Ali Luo, Jifeng Liu

Astrophysics of Galaxies

Aromatic rings in the Central Molecular Zone: Benzonitrile

V.M. Rivilla, D. San Andrés, M. Sanz-Novo et al. (+12 more)

In recent years, several aromatic molecules (benzene-based rings) have been detected in the cold molecular cloud TMC-1, with its CN-derivative, benzonitrile (c-C$_6$H$_5$CN), also identified in other nearby cold sources. However, observed abundances differ significantly from chemical model predictions, indicating an incomplete understanding of its chemistry and motivating searches in distinct environments. We report new detections of benzonitrile in two warmer molecular clouds of the Central Molecular Zone (CMZ): G+0.693-0.027 and G+0.633-0.0604. Using Yebes 40m ultra-deep surveys in the 31–50 GHz range, we performed LTE and non-LTE analyses to derive the physical parameters of the emission. We obtain column densities of $N$=(7.4$\pm$0.5)$\times10^{12}$ and (2.60$\pm$0.13)$\times10^{12}$ cm$^{-2}$, corresponding to abundances relative to H$_2$ of (6$\pm$1)$\times10^{-11}$ and (4.3$\pm$0.9)$\times10^{-11}$, consistent with values in cold Galactic clouds. The HC$_7$N/benzonitrile ratio is lower (2.15-2.4) than in colder sources (4.5-30), suggesting environmental effects and a relative enhancement of aromatic chemistry in the CMZ. These results confirm that benzonitrile is widespread and can survive in harsher environments (e.g., high temperatures, shocks, enhanced cosmic-ray ionization) than those in Galactic cold clouds. This suggests that aromatics are stable and abundant species that can significantly contribute to the total budget of interstellar carbon in molecular clouds. A top-down formation scenario, involving fragmentation of larger carbonaceous species, is consistent with the nearly constant abundances observed with molecular size.
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All authors V.M. Rivilla, D. San Andrés, M. Sanz-Novo, L. Colzi, I. Jiménez-Serra, A. López-Gallifa, A. Martínez-Henares, A. Megías, S. Martín, B. Tercero, S. Zeng, J. Loreau, M. Ben Khalifa, M. A. Requena-Torres, P. de Vicente

Solar and Stellar Astrophysics

Analyses on Wassenius' Report for Total Solar Eclipse in 1733: Quantifications of the Solar Radius and the Earliest Reported Prominences

Hisashi Hayakawa, Mitsuru Sôma, Noortje Peek et al. (+3 more)

Total solar eclipses (TSEs) offer a unique opportunity to observe the solar atmosphere, detect limb phenomena, and accurately measure the solar radius. Following the TSE in 1733, Wassenius first reported the existence of prominences to the scientific community. Wassenius' original manuscript is held in the Royal Academy Archives of Sweden; this study translates his report and documents the associated source materials and local eclipse visibility. The solar radius (R_Sun) during the TSE in 1733 are 696250 +/- 170 km and 959.99 +/- 0.24" in the absolute and apparent scales, respectively. This result contrasts with the modern standard (helioseismic) R_Sun of 695780 +/- 160 km and 959.34 +/- 0.22"; however, it is consistent with the solar radius recorded in 1715. The observed prominences are located at +23.5 +/- 22.5{\deg}, +66.5 +/- 22.5{\deg}, and -68.5 +/- 22.5{\deg} in the heliographic latitude. The appearance of prominences at such high latitudes contrasts with the sunspot butterfly diagram for 1725-1750, confirming 1733 as a solar minimum. These high-latitude prominences can potentially be attributed to the so-called 'polar rush' prominences that appear a few years after a solar minimum. If they are categorised as 'polar rush' prominences, the solar minimum must be re-dated to before 1733 May. Furthermore, the latitudes of at least two of the prominences reported by Wassenius enable their classification as quiescent prominences, suggesting the presence of a polarity inversion line in the polar regions in early 1733.
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All authors Hisashi Hayakawa, Mitsuru Sôma, Noortje Peek, Jean-Pierre Rozelot, Stanislav Gunár, Alexei Pevtsov

Astrophysics of Galaxies

Probing the Hot Gaseous Halos of Milky Way-like Galaxies in the TNG50 simulation

Zhijie Zhang, Xiaoxia Zhang, Taotao Fang et al. (+9 more)

The origin and structure of the hot ($T\gtrsim10^6$K) gaseous halo around Milky Way (MW)-mass galaxies provide a critical test for galaxy formation models. We perform a comprehensive comparison for a sample of MW analogues from the TNG50 cosmological simulation by generating synthetic soft X-ray emission and O VII/O VIII absorption lines, viewed from both internal (Solar) and external perspectives. The simulated halos successfully reproduce the observed global soft X-ray luminosity, inner-halo X-ray surface brightness, emission measure, and O VII absorption strength. However, two interconnected discrepancies are identified. First, the azimuthally averaged X-ray surface brightness profile from external viewpoints declines too steeply with radius compared to the extended emission detected in eROSITA stacking of SDSS galaxies, falling below the observations by up to $\sim 1$ dex at $R \gtrsim 100$ kpc. Second, the halos systematically underproduce O VIII absorption, with a median equivalent width $\sim 65\%$ lower than that observed in the Galactic halo, pointing to a deficit of hotter-phase gas at $T\sim(1.6-3.2)\times10^6$ K. These findings indicate that the simulated hot halos are too spatially compact and lack a hotter gas phase, suggesting that the TNG50 feedback model, while generating hot gas, deposits energy too centrally and too vigorously to sustain a gently extended, multi-phase corona.
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All authors Zhijie Zhang, Xiaoxia Zhang, Taotao Fang, Hui Li, Greg L. Bryan, Federico Marinacci, Paul Torrey, Mark Vogelsberger, Junfeng Wang, Haiguang Xu, Qingzheng Yu, Feng Yuan

Solar and Stellar Astrophysics

Hidden oscillations in plain sight: identification of seismically unresolved red-giant asteroseismic binary candidates

Jeong Yun Choi, Francisca Espinoza-Rojas and Saskia Hekker

Light curves of oscillating stars provide valuable insights into the stellar interiors. When oscillations from a pair of stars are captured within a single photometric aperture, they can be considered as potential asteroseismic binaries (ABs). If the two stars oscillate at similar frequency ranges, the superpositioned oscillation patterns appear as if from a single star, leading to inaccurate asteroseismic parameters. We investigate seismically unresolved AB candidates consisting of two red-giant stars observed by Kepler. We directly compare the power density spectra (PDSs) of blended and separated oscillations from both stars, and examine the impact of oscillations from two stars on asteroseismic and stellar parameters. We selected APOKASC3 stars with at least one neighboring source within 20 arcsec and show oscillations in similar frequency ranges. We focus on the systems where the light curves from each star in AB candidates are available or can be extracted with a custom mask. We identified 6 seismically unresolved AB candidates whose PDS morphologies change noticeably across light curves extracted with different apertures. Oscillations from two stars in a PDS cause inaccurate mode identification and bias the seismic parameters. These biases propagate into stellar properties: masses and radii for the 6 AB candidates differ by up to about 3 and 2 times relative to the individual stars, respectively. For the AB candidate with the most complex PDS, core properties become unreliable, with the coupling factor often being overestimated. We checked that all 6 AB candidates are chance alignments. Our results indicate that the inconsistencies in asteroseismic and stellar parameters across different studies can be explained by potential seismically unresolved ABs. We highlight the importance of identifying and accurately accounting for such systems in asteroseismic analysis.
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Astrophysics of Galaxies

Machine learning technique for morphological classification of galaxies from SDSS. IV. Visual inspection vs CNN for merging, irregular, edge-on, barred, ringed, and with dust lanes galaxies at 0.02<z<0.1

Dobrycheva D.V., Vavilova I.B., Kompaniiets O.V. et al. (+5 more)

Context. Convolutional neural networks (CNNs) are widely used for automated galaxy morphological classification in large surveys. However, projection effects, image artefacts, and intrinsic degeneracies limit reliable identification of detailed features, requiring large-scale visual validation. Aims. To visually inspect SDSS galaxies at 0.02 < z < 0.1 classified by a CNN as merging, irregular, edge-on, barred, ringed, or dust-lane galaxies; assess CNN completeness and failure modes; construct visually verified morphological catalogues; and determine nuclear activity types via BPT diagrams. Methods. We visually inspected all galaxies assigned by the CNN to six morphological classes: merging (2,574), irregular (9,432), edge-on (17,000), barred (6,000), ringed (13,882), and dust-lane (588), regardless of CNN probability. Refined samples were cross-matched with Galaxy Zoo 2; remaining galaxies were classified here for the first time. Nuclear activity was determined from SDSS DR17 spectra using H{\alpha}\alpha {\alpha}, He̱ta}\beta e̱ta}, [O III]\lambda$5007, and [N II] \lambda$6583 line ratios. Results. We present catalogues of 612 merging, 9,372 irregular, 16,822 edge-on, 575 dust-lane, 811 barred, and 2,150 ringed galaxies. CNN misclassifications stem primarily from projection effects, foreground stars, faint tidal features, and irregular star-forming structures. We characterise nuclear activity types for edge-on, barred, ringed, and dust-lane galaxies, finding systematic differences in LINER-like and composite fractions across subsamples. Five strong polar ring galaxy candidates were identified. Conclusions. Visual validation remains essential for refining CNN-based classifications. The resulting datasets support morphological studies, investigations of galaxy structure and secular evolution, and provide robust training samples for future machine learning models.
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All authors Dobrycheva D.V., Vavilova I.B., Kompaniiets O.V., Khramtsov V., Vasylenko M.Yu., Hetmantsev O.O., Melnyk O.V., Karachentseva V.E

Instrumentation and Methods for Astrophysics

An archive of reduced and telluric-corrected CRIRES+ L- and M-band spectra with slit-tilt and wavelength calibrations

Thomas Marquart and Alexis Lavail

The high-resolution near-infrared spectrograph CRIRES+ at ESO VLT covers the Y, J, H, K, L and M bands. The U-Ne and Fabry-Perot calibration light sources, however, only work up to the K-band, leaving the bands L and M without wavelength calibration, and without a way to measure the inclination of the long slit relative to the detector frame. To remedy this, we present here a uniformly reprocessed archive of all public CRIRES+ L/M science observations obtained between September 2021 and March 2025, totalling 11 131 raw frames. We use the telluric modelling tool viper that fits a model to the plethora of atmospheric absorption features that exist around these wavelengths. We calibrate the slit tilt from the wavelength solutions for the nodding A and B frames that have the target in the lower and upper half of the slit, respectively. We then update the static inputs to the data reduction system with the slit tilt information and reduce the data with the standard pipeline recipes. Subsequently, we derive new wavelength scales for each observation from telluric fits on the spectra themselves, additionally interpolating the solutions for spectra that have no tellurics from the ones that have. The resulting 5649 extracted, calibrated and telluric-fitted AB nod-pair spectra, spanning 156 unique targets from 68 ESO programmes, are served through an interactive web archive at https://www.astro.uu.se/crires-lm that offers data downloads and figures for all datasets that allow an initial judgement of the data quality.
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Astrophysics of Galaxies

Mapping the Milky Way with Gaia Bp/Rp spectra-IV: the broken and asymmetric density profile of the stellar disk traced by a large sample of red clumps

Wenbo Wu, Yuqin Chen, Jianhui Lian et al. (+10 more)

This study explores the density profile of the stellar disk, radially and azimuthally, based on approximately 8.4 million red clump stars selected from Gaia Bp/Rp spectra. After correcting for selection effects and distance uncertainties, we fit the vertical stellar density profile of the Galactic disk with a two-component model consisting of geometrically thin and thick disks. Our derived density profile shows several breaks radially: (1) a steep exponential inside R$\sim3$ kpc; (2) a nearly flat plateau from R$\sim3$ to $\sim7$ kpc; (3) an exponential decline beyond the solar radius to around 13 kpc; (4) a sharper exponential drop-off beyond R$\sim$13 kpc. The parameters of these four main components depend on $\phi$ to some extent. Variation of the termination radius of the first component suggests an interaction with the bar/bulge. Besides the typical flaring at $R>6.4$ kpc, we find that the thin disk also exhibits a similar and smooth thickening/flaring feature toward the Galactic center at $R<6.4$ kpc. The observed inner flaring may indicate heating effects introduced by the Galactic bar, since $R=6.4$ kpc lies close to the co-rotation radius where the bar's dynamical influence becomes significant. Additionally, we identify a localized density bump in the region $5<R<7$ kpc and $-30^\circ<\phi<15^\circ$, where a corresponding metallicity bump is also visible near the Galactic plane. This density/metallicity bump may be related to the recently reported bimodal distribution of the guiding radius of super metal-rich stars in the solar vicinity through radial migration.
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All authors Wenbo Wu, Yuqin Chen, Jianhui Lian, Martín López-Corredoira, Chengdong Li, Xianhao Ye, C. Allende Prieto, Xiang-Xiang Xue, Gang Zhao, Jingkun Zhao, David S. Aguado, Jonay I. González Hernández, Rafael Rebolo

Instrumentation and Methods for Astrophysics

Robust Angles-Only Initial Relative Orbit Determination Using Polynomial Optimization

Xingyu Zhou, Malcolm Macdonald, Roberto Armellin et al. (+2 more)

This paper develops a robust angles-only IROD method based on polynomial optimization for arbitrary nonlinear dynamics. First, the relative motion is approximated by high-order Taylor polynomials within the differential algebra framework, and the resulting cross-product-residual minimization problem is solved through a recursive polynomial optimization procedure. Second, a reduced-order weighting strategy is introduced by projecting the residual onto the two-dimensional tangent subspace of the line of sight, thereby structurally removing the intrinsic singularity of conventional three-dimensional weighting. Third, a zero-solution-avoidance constraint together with an adaptive threshold-selection mechanism is developed to improve robustness against poor initialization, strong measurement noise, and unfavorable observation geometries. Numerical simulations show that the proposed method improves IROD accuracy by about three orders of magnitude relative to the baseline methods, while also reducing the downstream orbit-refinement burden. The reduced-order weighting strategy further improves accuracy by about 43% in the nominal case and remains stable under large-noise conditions, outperforming the conventional three-dimensional weighting by about 81%.
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All authors Xingyu Zhou, Malcolm Macdonald, Roberto Armellin, Dong Qiao, Xiangyu Li

Astrophysics of Galaxies

CSST Preparations: Galaxy Completeness and Sérsic Profile Fitting across the Wide, Deep, and Extreme Fields

Ziqi Ma, Si-Yue Yu, Taotao Fang et al. (+3 more)

The upcoming imaging survey of the Chinese Space-station Survey Telescope (CSST) will deliver high-resolution imaging of an unprecedented number of galaxies for galaxy studies. To understand CSST's capability, and to support the preparation of early-science programs, we generate 470,526 mock CSST images for 22,406 simulated galaxies with $M_*>10^9 M_\odot$, whose parameters are calibrated to match real HST observations spanning photometric redshift $0<z\lesssim7$, across seven CSST filters and three planned survey depths: wide, deep, and extreme. We then perform source detection and Sérsic fitting. For point sources, we found that the 95% completeness magnitude in the g band reaches 26.3, 27.4, and 28.5 mag for the wide, deep, and extreme fields, respectively. For extended galaxies, their spatial extent dilutes the surface brightness, leading to brighter 95% completeness magnitudes of 24.4, 25.9, and 27.1 mag. The detection completeness remains above 95% at $z\lesssim3-4$ in the extreme field, while the corresponding redshift limits are $z\approx1$ in the deep field and $z\approx0.5$ in the wide field. Using three fitting codes, GALFIT, AstroPhot, and SourceXtractor++, we quantify measurement biases and uncertainties in galaxy magnitude ($m$), effective radius ($R_e$), effective surface brightness ($\mu_e$), Sérsic index ($n$), and axis ratio ($q$). On average, for fainter galaxies, the reduced signal-to-noise ratio leads to systematic overestimates in $m$, $R_e$, and $\mu_e$, and underestimates in $n$ and $q$. These biases, as well as the associated scatter, become progressively smaller in deeper fields. Overall, our results provide quantitative constraints on sample selection and the robustness of morphological measurements in CSST early-science and legacy surveys.
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All authors Ziqi Ma, Si-Yue Yu, Taotao Fang, Jinyi Shangguan, Zhao-Yu Li, Luis C. Ho

Cosmology and Nongalactic Astrophysics

Propagating data-driven galaxy redshift distribution uncertainties in 3$\times$2-pt analyses

Jaime Ruiz-Zapatero, Qianjun Hang, Yun-Hao Zhang et al. (+7 more)

Uncertainties in the radial distribution of galaxies, $\boldsymbol{n}(\boldsymbol{z})$, are one of the major contributions to the error budget of early Stage-IV galaxy survey analyses of weak gravitational lensing, galaxy clustering and galaxy-galaxy lensing (3$\times$2-pt). Based on ensembles of simulated $\boldsymbol{n}(\boldsymbol{z})$ including stochastic and systematic variations, we study the impact of four different $\boldsymbol{n}(\boldsymbol{z})$ uncertainty models: shifts, shifts & stretches, Gaussian processes (GP) and principal component analysis (PCA). Due to the high dimensionality of the latter models, we make use of state-of-the-art gradient-based inference methods as well as approximate analytical marginalisation schemes. Our results show that Stage-IV 3$\times$2-pt analyses must go beyond simple shift & stretch models. In particular, we advocate for the adoption of PCA models even in early Stage-IV surveys. Our results show that considering a five-parameters PCA model only degrades the constraint on the $S_{\rm 8}$ parameter by $5$ per cent with respect to the case when only a shift and a stretch parameter are included, while incurring half the bias in its constituents parameters, $\Omega_{\rm m}$ and $\sigma_{\rm 8}$. We demonstrate that all models considered can be safely marginalised analytically, with speed-ups of up to a factor of 25 depending on the dimensionality of the model. This will allow Stage-IV analyses to safely include higher-dimensional $\boldsymbol{n}(\boldsymbol{z})$ uncertainty models in their analysis at negligible additional computational cost.
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All authors Jaime Ruiz-Zapatero, Qianjun Hang, Yun-Hao Zhang, Benjamin Joachimi, Joe Zuntz, Ian Harrison, Carlos García-García, Alex Malz, Benjamin Stölzner, the LSST Dark Energy Science Collaboration

Solar and Stellar Astrophysics

The formation of circumbinary planets through disc fragmentation

Matthew Teasdale and Dimitris Stamatellos

Over 50 circumbinary exoplanets have been discovered in recent years, with several of them being gas giants on wide orbits ($>10$AU). The aim of this work is to investigate whether these planets can form through circumbinary disc fragmentation due to gravitational instability. We perform hydrodynamic simulations of marginally unstable (i) circumstellar discs, (ii) circumbinary discs with the same temperature profile as the circumstellar discs (fiducial model), and (iii) realistic circumbinary discs heated individually by each star of the binary. We find that discs around binaries with wider separations fragment earlier and more efficiently than those around closer binaries, and earlier than circumstellar discs. Realistic circumbinary discs form a larger number of protoplanets ($9\pm0.9$ protoplanets per disc), than fiducial circumbinary ($6.5\pm0.6$), and circumstellar discs ($7.5\pm0.8$). In realistic circumbinary discs, initial protoplanet masses are lower than those formed in circumstellar discs, and a larger fraction of them lie in the planetary-mass regime, favouring the formation of gas giant planets over brown dwarfs or low-mass stars. Fragmentation occurs predominantly beyond a binary-imposed forbidden region of $\sim50$AU, leading to final orbital radii peaking at $\sim100$AU. We also find that in circumbinary discs dynamical interactions eject a higher fraction of protoplanets than in circumstellar discs, producing free-floating objects, with ejection velocities on the order of $2-6~{\rm km s^{-1}}$. We conclude that gravitational fragmentation of circumbinary discs is a viable and potentially significant formation pathway for circumbinary gas giant planets.
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Solar and Stellar Astrophysics

The long-term outburst(s) of GPSV16: from an intermediate to a FUor classification

Carlos Contreras Peña, Jeong-Eun Lee, Philip W. Lucas et al. (+8 more)

FU Ori outbursts are thought to play a key role in stellar mass assembly and in the chemistry of protoplanetary disks during the early formation of stars. However, uncertainties remain regarding the universality of these events and the physical mechanism driving the high-amplitude variability. In this work, we present an analysis of optical, near- and mid-IR photometry (ZTF, UKIDSS GPS, NEOWISE) and near-IR spectra (IRTF, Gemini) of the eruptive variable Class I YSO GPSV16. The YSO, associated with the HII region G71.52$-$00.38 ($d=3.61$~kpc), showed two outbursts, one with $\Delta K_{\rm s}=2.2$~mag (2005-2012) and a second starting in 2016 with $\Delta K_{\rm s}=5.6$~mag and accretion luminosity of $\sim$130 L$_{\odot}$. The outbursts displayed distinct spectroscopic characteristics: the first showed emission lines associated with a hot inner disk surface, whereas the second showed absorption lines arising from the cooler upper layers of a viscously heated disk. These features likely arose due to the different accretion rates reached during each outburst. The second outburst showed a two-stage mid-IR rise, requiring $\approx8.4$ years to reach peak brightness. The mid-IR rise also started 8 years before the onset of the optical outburst. The wavelength-dependent light curve points to an instability that is triggered at larger distances within the accretion disk and propagates inward. Assuming a propagation time of 8 years for the accretion wave, we estimate that the second outburst started at a distance of $r\sim0.4$~AU. These results show how long-term, multi-wavelength photometric monitoring can help identify the disk instabilities that trigger eruptions in YSOs.
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All authors Carlos Contreras Peña, Jeong-Eun Lee, Philip W. Lucas, Gregory Herczeg, Doug Johnstone, Zhen Guo, Ho-Gyu Lee, Hwan-Ki Kim, Jessy Jose, Mizna Ashraf, Calum Morris

Instrumentation and Methods for Astrophysics

pyTANSPEC v1.0 and HxRGproc: Updated packages to Clean and Reduce TANSPEC data

Varghese Reji, Joe P. Ninan, Supriyo Ghosh et al. (+2 more)

TIFR-ARIES Near-Infrared Spectrometer (TANSPEC) is a spectrograph-cum-imager operating over the wavelength range $0.55 - 2.5~\mu$m. The instrument is mounted on the 3.6-m Devasthal Optical Telescope (3.6-m DOT). It offers two resolution modes: Low Resolution (LR) with $R\sim100-350$ and Cross-Dispersed (XD) via various slits of different widths (0.5", 0.75", 1.0", 1.5", 2.0" and 4.0"). The LR mode provides a resolving power ($R$) of $\sim 100-350$, while the XD mode achieves $R\sim2500$ using the 0.5" slit. The previous version of the data reduction pipeline supported only wavelength-calibrated XD mode spectra and was limited to two slits (S-0.5 and S-1.0). In this work, we present an upgraded version of pyTANSPEC. The upgraded pipeline not only improves the data extraction algorithm but also introduces several new features for users. It now enables the reduction of spectra from all available slits for both LR and XD modes. The upgraded version also implements a template-matching method for more precise wavelength calibration. Additionally, a step for flux calibration is also included. Alongside pyTANSPEC, we upgraded HxRGproc, a Python package for cleaning and generating slope images from Non-Destructive Readout (NDR) frames taken with H1RG and H2RG detectors. The package performs non-linearity correction, flags saturated pixels, removes pink noise, and eliminates cosmic ray events. HxRGproc is updated to work for the H2RG detector of TANSPEC and is set up on the TANSPEC server, ensuring users receive data that are pre-cleaned and non-linearity corrected.
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All authors Varghese Reji, Joe P. Ninan, Supriyo Ghosh, Devendra K. Ojha, Saurabh Sharma

Solar and Stellar Astrophysics

Fates of the sub-stellar objects (FOSSO) II. Evidence for Suppression of Metal Pollution in White Dwarfs by Close Substellar Companions

Zhangliang Chen, Xin-Yue Zhang, Di-Chang Chen et al. (+4 more)

Approximately 25–50% of white dwarfs (WDs) exhibit metal absorption lines in their photospheres, interpreted as evidence of ongoing/recent accretion of planetary debris from remnant systems. Previous theoretical studies have suggested that massive, close-in substellar companion may prevent delivery of larger bodies via dynamical interactions, thereby reducing white-dwarf pollution. However, no conclusive observational evidence has yet been established to confirm such a protective effect. In this work, based on a sample of 17 white dwarf-substellar companion (1–75 $M_{\rm J}$) systems with reliable spectroscopic classifications, we find that white dwarfs hosting close substellar companions (orbital period $P < 5$ d) exhibit a metal-pollution fraction of $7.7^{+11.3}_{-4.0}\%$, which is suppressed by a factor of $5.75^{+3.24}_{-1.94}$ (corresponding to a protection efficiency of $87.2^{+3.4}_{-9.2}\%$) relative to single white dwarfs with a confidence level of 99.96%. In contrast, white dwarfs with wider companions show a metal-pollution fraction of approximately $25.0^{+24.0}_{-12.8}\%$, comparable to that of single white dwarf systems. To interpret these results, we perform ensembles of N-body integrations and demonstrate that massive close-in substellar companions are capable of clearing 80%–90% of small-body contaminants. The good consistency between the observational statistics and dynamical simulations provides strong evidence for suppressed metal pollution in white dwarfs with close companions, and offers insights into the long-term dynamical evolution of WD remanent systems.
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All authors Zhangliang Chen, Xin-Yue Zhang, Di-Chang Chen, Kejun Wang, Bo Ma, Ji-Wei Xie, Ji-Lin Zhou

Astrophysics of Galaxies

Recovering extra-tidal open cluster members via multi-elemental chemical tagging

Andrès E. Piatti

The identification of open cluster (OC) members has been revolutionized by high-precision Gaia astrometry, yet traditional kinematic membership selections remain inherently conservative, often overlooking stars in tidal tails or those with perturbed velocities. This study investigates the reliability of these kinematic probabilities by searching for leaky cluster members – stars that fail standard kinematic membership criteria ($P < 0.7$) but possess chemical signatures identical to their host clusters. Using high-resolution spectroscopic data from the Gaia-ESO Survey, we established a seven-element chemical fingerprint ([Fe/H], Li, Si, Ca, Ti, Co, and Ni) for 34 OCs. We identified a sample of 63 stars across 22 clusters that are chemically indistinguishable from their host populations despite being kinematically rejected by standard algorithms. By cross-referencing these targets with Jacobi radii (rJ) derived from modern Milky Way potential models, we find that 35% are located in extra-tidal regions (d > rJ), providing direct evidence of active cluster dissolution and tidal debris. The remaining 65% are located within the Jacobi radius, suggesting that their kinematic rejection is likely due to orbital motion in unresolved binary systems. These results demonstrate that chemical tagging is a critical tool for overcoming the spatial and kinematic biases of astrometric catalogues. By recovering these lost members, we provide a more complete census of cluster mass loss and underscore the necessity of a hybrid chemical-kinematic approach to map the transition of stars from bound systems to the Galactic field.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Pre-localization of Massive Black Hole Binaries in the Millihertz Band

Xue-Ting Zhang, Jonathan Gair, Chris Messenger et al. (+3 more)

The space-borne gravitational-wave (GW) detectors will open a new mass and redshift regime, allowing us to observe massive black hole binaries (MBHBs) throughout the Universe. A subset of these systems is expected to produce electromagnetic (EM) counterparts, offering a unique opportunity to follow the continuous evolution of massive black holes through joint GW and EM observations. Realizing this potential, however, requires low-latency, high-throughput data-analysis pipelines that can extract reliable source parameters and sky localizations from space-borne data streams fast enough to trigger EM follow-up. In this work we develop a fast, normalising flow-based inference pipeline designed for early-warning analysis of MBHB signals in a TianQin-like configuration. Our method combines a learned embedding of the detector time series with a neural spline flow (NSF) to perform amortized Bayesian inference, producing posterior samples for the main source parameters in roughly one minute per event. For a representative MBHB whose merger occurs $\sim 15$ minutes after the end of the analyzed GW observation, the pipeline achieves pre-merger sky localizations of order $\sim 20~\mathrm{deg}^2$, recovers the same number of sky modes as a reference parallel-tempered Markov chain Monte Carlo (PTMCMC) analysis, and yields parameter uncertainties of comparable scale, while still operating within a practically useful pre-merger warning window. These results demonstrate that NSF-based inference can deliver accurate, near-real-time parameter estimation for space-borne MBHB GW signals, and that the resulting early-warning localizations are sufficiently precise to make rapid EM follow-up.
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All authors Xue-Ting Zhang, Jonathan Gair, Chris Messenger, Natalia Korsakova, Yi-Ming Hu, Hong-Yu Chen

Cosmology and Nongalactic Astrophysics

The FLAMINGO simulations data release

John C. Helly, Robert J. McGibbon, Joop Schaye et al. (+15 more)

We describe the public release of $>2.3$ petabytes of data from the FLAMINGO cosmological simulations. The suite consists of hydrodynamical simulations that include radiative cooling, star formation, stellar mass loss and the resulting chemical enrichment, supernova feedback, and two implementations of AGN feedback. Neutrinos are simulated explicitly using particles. Data products include snapshots, halo and galaxy catalogues, HEALPix all-sky lightcone maps, particle data for lightcone maps, and power spectra. The FLAMINGO set includes 22 hydrodynamical simulations. In addition, there are 16 gravity-only simulations, including the $10080^3$ particles FLAMINGO-10k run, with initial conditions that match those of the corresponding hydrodynamical runs. The fiducial hydrodynamical simulations span three numerical resolutions that have each been calibrated to reproduce the present-day galaxy stellar mass function and gas fractions in low-redshift clusters. Other simulations systematically vary the galaxy stellar mass function, cluster gas fractions, cosmology (including neutrino masses), and/or the nature of dark matter, in volumes of 1Gpc$^3$. The release includes hitherto unpublished simulations that use extra dark matter particles. While we provide a facility for downloading complete simulation outputs, we recognise that for many users this will not be possible due to limited local storage or network bandwidth. We implement a web service that enables users to explore available outputs and selectively download datasets or parts of datasets.
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All authors John C. Helly, Robert J. McGibbon, Joop Schaye, Matthieu Schaller, William McDonald, Joey Braspenning, Jeger C. Broxterman, Emily E. Costello, Willem Elbers, Victor J. Forouhar Moreno, Carlos S. Frenk, Adrian Jenkins, Roi Kugel, Ian G. McCarthy, Jaime Salcido, Marcel P. van Daalen, Bert Vandenbroucke, Tianyi Yang

Solar and Stellar Astrophysics

Thermal instability in coronal loops: linking eigenvalue spectra to time-dependent evolution

Adrian Kelly, Rony Keppens and Jordi De Jonghe

Cool, dense condensations such as coronal rain and prominences suggest that coronal plasma can undergo runaway radiative cooling. Connecting this behaviour to linear thermal modes requires us to fully understand the deeper connection between eigenvalue spectra and actual time-dependent evolution. We aim to clarify this intricate link for a simplified, coronal-only model of a stratified coronal loop by combining spectral, linear initial-value, and nonlinear simulations of the same loop setup. We study waves and instabilities, as well as temporal evolutions for a 1D hydrostatic, thermally balanced loop with optically thin radiation and prescribed heating. The non-adiabatic spectrum is computed with our open-source Legolas code. We demonstrate our newly developed boundary value-initial value solver Legolas-IVP, where linear evolutions are performed for controlled perturbations, and fully equivalent nonlinear runs are carried out with MPI-AMRVAC. The spectrum contains discrete acoustic modes and a thermally unstable branch including a thermal continuum. Linear initial-value experiments with isochoric, isobaric, and isentropic pulses highlight how the polarisation of the eigenmodes demonstrates physically consistent behaviour expected from the eigenspectrum. Even in the linear stage, thermal imbalance drives siphon-like flows toward the cooling region. Growth rates from Legolas-IVP agree with spectral predictions and are reproduced in MPI-AMRVAC, which follows the condensation through runaway cooling to chromospheric temperatures, with the cool dense blob sliding under gravity toward the loop footpoint. The spectral-linear-nonlinear investigation demonstrates a direct link between thermal eigenmodes and condensation dynamics, providing a basis for extending to fully 3D MHD models.
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High Energy Astrophysical Phenomena

The GRB joint scientific analysis pipeline of the ECLAIRs and GRM instruments on board SVOM

F. Piron, F. Daigne, T. Maiolino et al. (+36 more)

The study of the prompt high-energy emission of Gamma-Ray Bursts (GRBs) with SVOM relies on the observations performed by ECLAIRs (4-150 keV) and the Gamma-Ray Monitor (GRM, 0.015-5 MeV), the two wide field-of-view instruments on board the satellite. In this article, we introduce the eclgrm pipelines running at the French Science Center of SVOM, which combine the ECLAIRs and GRM data to generate scientific data products describing the GRB broad-band temporal and spectral properties. The architecture of the pipelines is presented, as well as their activation following each onboard trigger, and their workflow. The statistical data analysis methods employed by the pipelines are described, along with the scientific data products that are created in real time or from the full event data. We also present the eclgrm-ui user interface which allows the scientists on shift to monitor the automated data processings in the pipelines, and to optimize the analysis results interactively.
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All authors F. Piron, F. Daigne, T. Maiolino, P. Maeght, U. Jacob, M.G. Bernardini, D. Corre, J. Wang, F. Lacreu, G. Tcherniatinsky, L. Domisse, T. Barlyaeva, A. Maïolo, J.-L. Atteia, L. Bouchet, M. Brunet, J.-P. Dezalay, O. Godet, S. Guillot, H. Yang, B. Arcier, S. Mate, N. Dagoneau, L. Jouvin, K. Tazhenova, T. Sadibekova, P. Bacon, N. Bellemont, F. Cangemi, A. Coleiro, J. He, Y. Huang, L. Li, H. Shi, J. Wang, P. Wang, L. Zhang, X.-Y. Zhao, S. Zheng

Instrumentation and Methods for Astrophysics

SVOM/C-GFT: Instrumentation and Performances on the SVOM Alerts

Chao Wu, Zhe Kang, Xiao-Meng Lu et al. (+20 more)

The Chinese Ground Follow-up Telescope (C-GFT) is an optical facility upgraded to support the Space Variable Objects Monitor mission (SVOM). Located at the Jilin Observation Station, it is capable of rapidly identifying and monitoring the optical counterparts of Gamma-Ray Bursts (GRBs). The 1.2-m telescope is equipped with two switchable focal-plane instruments: the prime-focus wide-field LATIOS camera and the Cassegrain-focus three-channel CATCH camera. In this paper, we present a system overview, including the observatory, the telescope, the instrumentation, the automated operational framework managed by the Operations Center, and the data processing pipelines. We also report the performance results obtained during over one year of SVOM's post-launch operations. The results demonstrate that the system meets its design specifications and delivers robust observational and operational performance.
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All authors Chao Wu, Zhe Kang, Xiao-Meng Lu, Xu-Hui Han, Li-Ping Xin, Pin-Pin Zhang, You Lv, Cheng-Wei Zhu, Ruo-Son Zhang, Jin-Song Deng, Yu-Lei Qiu, Mao-Hai Huang, Hong-Bo Cai, Hai-Bo Hu, Lei Huang, Lei Jia, Yu Luo, Jing Wang, Mo Zhang, Si-Cheng Zou, Zhen-Wei Li, Cheng-Zhi Liu, Jian-Yan Wei

Instrumentation and Methods for Astrophysics

SVOM/VT: On-ground processing of VT-VHF data

Chao Wu, Jesse T. Palmerio, Tatyana Sadibekova et al. (+14 more)

The VT–VHF data comprise three types of onboard-processed data results generated from four sequential observational sequences and transmitted to the ground via a Very High Frequency (VHF) downlink. On the ground, these data are processed by three successive pipelines: the pre-processing pipeline, the VT–VHF data processing pipeline (VVPP), and the VT afterglow candidate pipeline (VTAC). These pipelines perform packet decoding, astrometric and photometric calibration, and afterglow candidate identification, respectively. This paper describes the architecture and operational implementation of the VT–VHF ground processing system and assesses its end-to-end performance using the first year of SVOM operations. These data enable rapid identification of GRB optical counterparts. Early detections, while the source is still optically bright, facilitate spectroscopic redshift measurements. Dual-band colors provide preliminary redshift constraints and help identify high-redshift candidates, whereas non-detections in both bands may indicate very high redshift, significant extinction, or intrinsically dark bursts. In-orbit operations show that the VT–VHF ground processing system successfully identifies optical afterglow candidates for a significant fraction of ECLAIRs triggers with available VT–VHF data, demonstrating its robustness and readiness.
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All authors Chao Wu, Jesse T. Palmerio, Tatyana Sadibekova, Yannis Canton, Kamshat Tazhenova, Susanna Diana Vergani, Li-Ping Xin, Yu-Lei Qiu, Henri Louvin, Mo Zhang, Mao-Hai Huang, Isabelle Jegouzo, Hua-Li Li, Hong-bo Cai, Jin-Song Deng, Bertrand Cordier, Jian-Yan Wei