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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 27 April

Instrumentation and Methods for Astrophysics

SVOM/VT: Real-Time Onboard Data Processing

Hong-Bo Cai, Yu-Lei Qiu, Li-Ping Xin et al. (+16 more)

The SVOM Visible Telescope (VT) is critical for the rapid identification of gamma-ray burst (GRB) optical counterparts, particularly for high-redshift candidates that require immediate infrared spectroscopic follow-up. To address the stringent bandwidth constraints of the VHF downlink while ensuring real-time data availability, we developed the VT Onboard Data Processing Pipeline (VOPP).This paper details the software architecture, algorithms, and hardware implementation of VOPP using an FPGA and a CPU. The pipeline performs essential real-time tasks, including image quality assessment, dark and flat-field correction, and optimized image stacking to mitigate cosmic ray contamination and variable background noise. Furthermore, it generates compact source catalogs and highly compressed 1-bit images to facilitate rapid downlink.In-flight performance analysis confirms the pipeline's robustness, demonstrating the availability of VT VHF data for 78 percent of promptly slewed SVOM GRBs, with 56 percent leading to the identification of optical counterparts, typically within 18 minutes post-trigger.
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All authors Hong-Bo Cai, Yu-Lei Qiu, Li-Ping Xin, Zheng-Yang Bian, Rui-Feng Su, Qing-Yun Mao, Bin-Ping Su, Jun-Wang He, Wei Gao, Jian Zhang, Li-Jun Dan, Kun Chen, Dong Li, Chao Wu, Hua-Li Li, Jin-Song Deng, Yong-He Zhang, Jian-Yan Wei, Bertrand Cordier

Instrumentation and Methods for Astrophysics

SVOM/VT: Flight Model Verification and Pre-launch Testing

Jian Zhang, Xue-Wu Fan, Gang-Yi Zou et al. (+23 more)

This paper presents pre-launch testing and calibration results for the SVOM/VT (Space-based Variable Objects Monitor, Visible Telescope) Flight Model (FM), validating its performance under simulated space conditions through thermal vacuum cycling, energy concentration analysis, stray light suppression, and CCD/electronics calibrations (gain, noise, quantum efficiency). The results confirm full compliance with design requirements: stray light suppression achieves point-source transmittance $<10^{-7}$ at $30^\circ$ off-axis, thermal control maintains stable CCD temperatures ($-75^\circ$C for the red channel, $-65^\circ$C for the blue channel), and detection sensitivity meets the limiting magnitude of 22.50 (SNR $>$ 3 with 300 seconds exposure). Early in-orbit tests further validate performance, yielding limiting magnitudes of 22.70 (V-band, red) and 22.78 (blue), consistent with pre-launch specifications.
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All authors Jian Zhang, Xue-Wu Fan, Gang-Yi Zou, Yu-Lei Qiu, Wei Gao, Wei Wang, Chen-Jie Wang, Ning Qi, Jin-Song Deng, Li-Jun Dan, Yue Pan, Chao Huang, Yun-Fei Du, Guo-Rui Ren, Zhong-Han Sun, Feng-Tao Wang, Wei Li, Bao-Peng Li, Chao Shen, Peng-Fei Chen, Kun Chen, Hui Zhao, Ming Chang, Tao Wang, Li-Pin Xin, Jian-Yan Wei

Instrumentation and Methods for Astrophysics

GRM Scientific Pipeline

Ping Wang, Li Zhang, Jin Wang et al. (+18 more)

The Gamma-Ray Monitor (GRM) is a key payload of the Space-based multiband astronomical Variable Objects Monitor (SVOM) mission, which is designed to detect gamma ray bursts (GRBs) within the energy range of 15 keV to 5 MeV. The GRM Instrument Center (GRM\_IC) features real-time data processing through the X-band, enabling rapid response of high-energy GRB events. The system employs an event-driven architecture and distributed design, achieving efficient processing and real-time monitoring of massive observational data. Through comprehensive data production processes and scientific data product management, the system achieves efficient production of scientific data products of the L1B / C level through the submission of jobs to the task scheduling system. Through modular architecture design and automated processing workflow, the GRM data processing system realizes precise conversion and scientific analysis of GRB detection data, providing robust technical support for future system upgrades and cross-platform collaboration.
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All authors Ping Wang, Li Zhang, Jin Wang, Wen-Hui Yu, Xiao-Yun Zhao, Shi-Jie Zheng, Shao-Lin Xiong, Yue Huang, Jiang He, Hao-Li Shi, Lu Li, Yong-Wei Dong, Min Gao, Jiang-Tao Liu, Xin Liu, Jian-Chao Sun, Li-Ming Song, Bo-Bing Wu, Jin-Zhou Wang, Rui-Jie Wang, Shuang-Nan Zhang

High Energy Astrophysical Phenomena

SVOM/VT: Overview of data processing and GRB identifications with X-band data

Hua-Li Li, Yu-Lei Qiu, Li-Ping Xin et al. (+16 more)

VT (the Visible Telescope) is an optical telescope onboard the SVOM (Space-based Multi-band Astronomical Variable Objects Monitor) mission, specifically designed to detect optical counterparts of gamma-ray bursts (GRBs), study their afterglows, and select high-redshift candidates. It performs rapid follow-up observations simultaneously in two channels either via autonomous platform slewing or Target of Opportunity (ToO) observations. The science images acquired by VT and transmitted via the X-band downlink system are designated as VT X-band data. This paper provides an overview of GRB optical afterglow identifications with VT and describes the ground-based processing pipeline for VT X-band data, including preprocessing, astrometric calibration, and photometry. Up to 2025 December 3, VT has followed up 111 GRBs triggered by SVOM or external missions. The overall detection rate of optical counterparts is approximately 75%. Specifically, for bursts detected by SVOM/ECLAIRs, the detection rate is 77% when observed by VT within 30 minutes after the burst. A slightly higher detection rate of 81% is achieved for GRBs triggered by external missions through rapid ToO observations with a mid-time of less than 3 hours.
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All authors Hua-Li Li, Yu-Lei Qiu, Li-Ping Xin, Chao Wu, Zhu-Heng Yao, Yi-Nuo Ma, Yang Xu, Pin-Pin Zhang, Xu-Hui Han, Jing Wang, Hong-Bo Cai, Da-Wei Xu, Jesse T. Palmerio, Mao-Hai Huang, Jia-Li Zhu, Mo Zhang, Jin-Song Deng, Bertrand Cordier, Jian-Yan Wei

Instrumentation and Methods for Astrophysics

SVOM Real-time Response and Collaboration System

Meng Bai, Boquan Li, Ju Su et al. (+6 more)

The SVOM mission (Space-based multi-band astronomical Variable Objects Monitor) is a Franco-Chinese mission dedicated to the study of the most distant explosions of stars, the gamma-ray bursts. Here, we introduce the real-time response and collaboration system of SVOM, with the adoption of the BeiDou-3 short message communication service. We present the SVOM on-board and on-ground system designs and data flow, together with the collaboration mechanism with other missions. In the first year of the in-flight operation, SVOM has detected 172 gamma-ray bursts, including 147 by the GRM instrument and 62 by the ECLAIRs instrument. At the same time, SVOM has performed 1040 observations, including 122 ToO-EX(Target of Opportunity-Exceptional) observations, 48 ToO-MM(Target of Opportunity-Multi-messenger) observations and 870 ToO-NOM(Target of Opportunity-Nominal) observations. All these have increased the scientific output of the mission.
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All authors Meng Bai, Boquan Li, Ju Su, Zhun Feng, Yichuan Man, Zhigang Xiao, Meng Zhang, Yurong Li, Tai Hu

Instrumentation and Methods for Astrophysics

Alert Chain and Observation Planning for Ground Wide Angle Camera Network

Xu-hui Han, Pin-pin Zhang, Yu-jie Xiao et al. (+10 more)

The Ground Wide Angle Camera Network (GWAC-N) is a robotic telescope network. It consists of ten wide-field core telescopes (GWAC-A) and two 60cm narrow-field rapid follow-up telescopes (GWAC-F60A/B). The primary scientific goal of GWAC-N is to detect optical counterparts of gamma-ray bursts (GRBs) discovered by the SVOM satellite. This is achieved through synchronized monitoring with the GWAC-A array. Upon receiving a GRB trigger alert, the network conducts rapid, multi-band follow-up observations using the GWAC-F60A/B telescopes. The two-stage observation process involves many telescopes, making manual control impractical. Automated operations are therefore essential. They are realized through an integrated alert processing chain and an automated observation scheduling and dispatching mechanism. To enable this, we employ the SVOM Follow-up Observation Coordinating Service (FOCS) and GWAC-N's Automatic Observation Management (AOM) system. This paper presents the integrated alert processing workflow. It also describes the formulation of observation strategies, and the scheduling and execution of observations enabled by FOCS and AOM.
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All authors Xu-hui Han, Pin-pin Zhang, Yu-jie Xiao, Li-ping Xin, Ruo-song Zhang, Lei Huang, Xiao-meng Lu, Hong-bo Cai, Yang Xu, Wen-long Dong, Hua-li Li, Ya-tong Zheng, Jian-yan Wei

Instrumentation and Methods for Astrophysics

The VHF alert network of the SVOM mission

B. Cordier, L. Jeannin, Ph. Lafabrie et al. (+9 more)

The scientific success of the SVOM mission will rely on the rapid transmission of alert messages from the satellite to the scientific community, and in particular to the ground-based instruments supporting the mission. In this paper, we present the alert system developed for SVOM which relies on the rapid transmission of alert messages through the transfer of data packets from an onboard VHF-band radio transmitter to a network of radio receivers deployed along the satellite ground track. We will successively detail the antenna design, radio performance, network deployment, its integration within the French data center, as well as the performance achieved after one year of operation in terms of availability and latency.
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All authors B. Cordier, L. Jeannin, Ph. Lafabrie, G. Chavanas, S. Crepaldi, N. Dagoneau, A. Formica, V. Garcia, L. Jolivet, S. Lacour, H. Louvin, E. Sabatier

High Energy Astrophysical Phenomena

In-flight performance of the MXT Camera

M. Moita, A. Meuris, P. Ferrando et al. (+8 more)

On-board the SVOM mission, the Microchannel X-ray Telescope observes the soft X-ray band of the gamma-ray bursts afterglows. The so-called lobster-eye optics focuses X-rays to the camera subsystem that performs imaging and spectroscopy of a region of the sky 58x58 arcmin2 wide centered on the burst detected by the ECLAIRs instrument. The recorded photon positions are used by the on-board scientific software to rapidly localize the source, whereas spectral information is used on ground to model the properties of the gamma-ray bursts. The first months in orbit were intensively used to tune the parameter settings of the detector and the calibration method to provide high availability of the camera and accurate spectroscopy to the users. The paper presents the design of the camera validated by on-ground testing, the tuning phase in flight and the performance of the camera at the beginning of the mission. Perspectives are given concerning the evolution of the spectral response during the mission.
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All authors M. Moita, A. Meuris, P. Ferrando, A. Sauvageon, H. Goto, D. Götz, C. Plasse, L. Godinaud, A. Fort, K. Mercier, S. Crepaldi

High Energy Astrophysical Phenomena

The coded mask of the ECLAIRs telescope onboard the SVOM space mission

C. Lachaud, A. Givaudan, M. Karakac et al. (+9 more)

ECLAIRs is a hard X-ray coded-mask telescope onboard the SVOM space mission, designed to detect and localize high-energy transients, in particular gamma-ray bursts. Operating over the 4-150 keV energy range, ECLAIRs extends coded-mask imaging to an unusually low-energy threshold. Achieving sensitivity down to 4 keV while maintaining performance up to 150 keV motivated the development of a novel self-supporting coded mask. This design addresses both scientific and mechanical challenges through dedicated pattern-generation algorithms and an innovative stiffened sandwich structure. We present the rationale, development, and final implementation of the ECLAIRs coded mask.
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All authors C. Lachaud, A. Givaudan, M. Karakac, W. Bertoli, S. Dheilly, C. Juffroy, C. Chapron, A. Gros, S. Schanne, S. Begoc, P. Guillemot, H. Pasquier

Instrumentation and Methods for Astrophysics

Overview of Ground-based Wide-Angle Cameras array

Liping Xin, Lei Huang, Hongbo Cai et al. (+25 more)

As one of the key ground-based facilities of the Chinese-French SVOM mission, the main scientific objectives of the Ground-based Wide Angle Camera array (GWAC) are to detect prompt optical emission of gamma-ray bursts or other short duration astronomical transients on a second-scale temporal resolution. GWAC is located at Xinglong observatory, China, and consists of 10 mounts and 40 cameras, providing a joint field of view of about 3600 square degrees.The detection ability is 16 magnitude in 10 seconds of exposure time in the visual band under the condition of the new moon phase. Here, we give an overview of GWAC and introduce the science motivation of the project, as well as the performance of the hardware and the software. The observation strategies and the data processing are briefly presented. The early sciences in the last 5 years since the first light are summarized.
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All authors Liping Xin, Lei Huang, Hongbo Cai, Xuhui Han, Yang Xu, Xiaomeng Lu, Huali Li, Jing Wang, Yulei Qiu, Chao Wu, Ruosong Zhang, Pinpin Zhang, Yujie Xiao, Guangwei Li, Jingsong Deng, Dawei Xu, Linjun Wang, Jinran Xu, Yinuo Ma, Yangtong Zheng, Wenlong Dong, Zhuheng Yao, Enwei Liang, Xianggao Wang, Xiangyu Wang, Zigao Dai, Yuangui Yang, Jianyan Wei

Instrumentation and Methods for Astrophysics

COLIBRI (SVOM/FM-GFT): Instrumentation and Performances on the SVOM Alerts

S. Basa, W. H. Lee, A. M. Watson et al. (+71 more)

COLIBRI, the French Mexican Ground Followup Telescope (FM GFT) for SVOM, is a 1.3 meter rapid response optical facility specifically developed for prompt, multiband observations of GRB afterglows and for delivering subarcsecond localisations of optical counterparts for detailed followup studies. The telescope operates through a fully automated system that manages the entire workflow, from alert reception to counterpart identification. Commissioning results confirm that the telescope meets design specifications, and this paper presents a comprehensive performance assessment of the capabilities.
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All authors S. Basa, W. H. Lee, A. M. Watson, F. Dolon, J. Floriot, J.-L. Atteia, D. Dornic, E. E. Lugo-Ibarra, L. Figueroa, R. Langarica, H. Valentin, M. Ageron, F. Agneray, L. C. Alvarez Nunez, C. Angulo-Valdez, S. Antier, T. Auphan, M. Baumann, L. Bautista, R.L. Becerra, S. Benahmed, H. Benamar, C. Blanpain, O. Boulade, Y. Bounab, J. Boy, N.R. Butler, E. O. Cadena Zepeda, S. Cuevas, A. de Ugarte Postigo, C. Delisle, M. Devigny, J.G. Ducoin, F. Fortin, J. Fuentes-Fernandez, C. Gaiti, L. Garcia-Garcia, P. Gallais, R. Gill, N. Globus, G. Guisa, E. Kajfasz, D. Lafforgue, A. Langlois, M. Larrieu, J. Landa, J. Lecubin, D. Lopez-Camara, E. Lopez Angeles, S. Lombardo, F. Magnani, N. Mandarakas, A. Malgoyre, R. Mathon, E. Moreno Mendez, C. Moreau, A. Nouvel de la Fleche, J. L. Ochoa, L. Ortiz, M. H. Pedrayes-Lopez, M. Pereyra, L. Provost, P. Ramon, N.A. Rakotondrainibe, S. Ronayette, J. Ruiz Diaz-Soto, F. Sanchez Alvarez, B. Schneider, A. Secroun, N. Striebieg, S. Tinoco, M. Tourner-Sylvain, F. Valenzuela, D. Vincent

Instrumentation and Methods for Astrophysics

SVOM Ground Support System

Yurong Liu, Meng Bai, Mingyue Wei et al. (+3 more)

The Ground Support System (GSS) is a critical component of the Space-based multi-band astronomical Variable Objects Monitor (SVOM) mission's ground segment. Its main tasks include organizing and implementing the operations and management of the SVOM payloads, receiving scientific data, as well as preprocessing and managing the scientific data. To address the specific requirements of the SVOM mission, including specialized mission planning, data reception, status monitoring, and product processing, a dedicated SVOM Ground Support System has been designed based on the integrated architecture of the Chinese Space Science Satellite Project Ground Support System. This system has successfully supported SVOM's launch and on-orbit operations.
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All authors Yurong Liu, Meng Bai, Mingyue Wei, Ke Feng, Boquan Li, Tai Hu

High Energy Astrophysical Phenomena

The SVOM mission, its profile and its system

B. Cordier, J. Y. Wei, S. N. Zhang et al. (+37 more)

The SVOM (Space-based Variable Objects Monitor) mission, launched into low Earth orbit on 22 June 2024, is a French-Chinese multi-wavelength observatory dedicated to the study of the transient sky. Inspired by the Neil Gehrels Swift Observatory, it consists of an autonomous rapid-slewing satellite, linked in real time to several ground-based telescopes. The space segment comprises two X-ray/gamma-ray wide-field instruments (ECLAIRs and GRM) with real-time triggering capabilities combined with two narrow-field telescopes in X-ray (MXT) and in visible (VT). In addition, the SVOM collaboration has also developed a unique visible and NIR ground-based follow-up system to promptly respond to the gamma-ray transients detected on board. The core program of SVOM will provide new insights into the Gamma-Ray Burst physics by providing a homogeneous dataset covering both the prompt and afterglow emissions, as well as better studying the low luminosity and soft Gamma-Ray Burst populations. As a versatile satellite platform with fast slewing capabilities, SVOM also comprises a Target of Opportunity program and a General Program consisting in pointed observations scheduled over the year that will both significantly contribute to the multi-messenger and time-domain astronomy.
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All authors B. Cordier, J. Y. Wei, S. N. Zhang, S. Basa, J. -L. Atteia, A. Claret, A. Coleiro, F. Daigne, N. Dagoneau, J. S. Deng, Y. W. Dong, O. Godet, D. Gotz, X. H. Han, C. Lachaud, E. W. Liang, F. Piron, Y. L. Qiu, S. Schanne, D. Turpin, S. D. Vergani, J. Wang, C. Wu, L. P. Xin, B. Zhang, M. Bai, S. Crepaldi, K. Feng, F. Gonzalez, M. Huang, D. Li, Y. Liu, H. Louvin, K. Mercier, J. Jaubert, R. Sun, M. Y. Wei, X. F. Zhang, Y. Zhang, the SVOM collaboration

High Energy Astrophysical Phenomena

SVOM/VT: Preliminary Calibration Analysis

Zhu-Heng Yao, Yu-Lei Qiu, Jin-Song Deng et al. (+9 more)

We present the in-orbit calibration of the Visible Telescope (VT), one of the key instruments aboard the Space Variable Objects Monitor (SVOM) mission for gamma-ray burst (GRB) studies. Using Gaia Data Release 3 (DR3) as a reference, the VT achieves an astrometric precision better than 0.03” for bright stars, degrading to ~0.25” for faint targets. Shortly after launch, contamination was detected, reducing system transmission by ~40%. An initial bake-out successfully restored performance, but gradual recontamination caused transmission to decline by ~20% over the following 100 days before stabilizing. Despite this effect, routine standard star observations maintain precise zero-point calibration, ensuring a photometric stability of 0.02 mag. Using synthetic stellar spectra, we derived photometric transformations to the Gaia, SDSS, and Johnson-Cousins systems with typical residuals of 0.03 mag. These results demonstrate the VT system's capability and reliability in calibrating GRBs and other transients.
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All authors Zhu-Heng Yao, Yu-Lei Qiu, Jin-Song Deng, Li-Ping Xin, Chao Wu, Hua-Li Li, Jing Wang, Yi-Nuo Ma, Hong-Bo Cai, Xu-Hui Han, Jian-Yan Wei, Betrand Cordier

High Energy Astrophysical Phenomena

Overview of the ECLAIRs Trigger for SVOM gamma-ray burst detection

S. Schanne, F. Château, N. Dagoneau et al. (+3 more)

The French-Chinese SVOM satellite mission (Space-based multi-band astronomical Variable Objects Monitor) was launched in mid-2024, with science objectives focused on the detection and study of astrophysical transient events, primarily Gamma-Ray Bursts (GRBs). The onboard trigger of the hard X-ray wide-field coded-mask instrument ECLAIRs autonomously detects and localizes GRBs on SVOM and requests automatic spacecraft slews toward these sources, enabling follow-up observations by the onboard narrow field-of-view instruments MXT and VT. The trigger also transmits real-time alerts via the SVOM VHF network to the ground, allowing rapid follow-up campaigns by the broader community, including multiple space- and ground-based facilities. We present an overview of the ECLAIRs trigger, with emphasis on the two trigger algorithms running simultaneously onboard: the Count-Rate Trigger (CRT) and the Image Trigger (IMT), both of which issue alerts for GRBs localized on the sky. The trigger has already detected several notable events, including both classical GRBs and peculiar X-ray-rich GRBs, enabling numerous redshift measurements, including high-redshift bursts.
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All authors S. Schanne, F. Château, N. Dagoneau, F. Daly, H. Le Provost, P. Kestener

High Energy Astrophysical Phenomena

The SVOM / ECLAIRs Scientific Analysis Pipeline

A. Goldwurm, P. Bacon, N. Bellemont et al. (+10 more)

This paper reports on the scientific pipeline for the analysis of the ECLAIRs data of the SVOM mission. We describe the overall procedure, the different steps and the main algorithms of the data analysis for this hard X-ray coded mask instrument. The pipeline runs in automatic mode at the science center generating standard products but can also be used off-line with specific choices of parameters. Generated data products and preliminary performances are illustrated along with perspectives for future improvements.
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All authors A. Goldwurm, P. Bacon, N. Bellemont, F. Cangemi, C. Cavet, A. Coleiro, A. Foisseau, A. Gros, C. Lachaud, S. Le Stum, T. Bouchet, J. Rodriguez, L. Bouchet

Instrumentation and Methods for Astrophysics

SVOM/ECLAIRs detection plane: main features and performance

O. Godet, J.-L. Atteia, R. Pons et al. (+21 more)

The detection plane of the high-energy transient camera ECLAIRs onboard SVOM is made of 200 XRDPIX detection modules, each consisting of a matrix of $8\times 4$ Schottky-type CdTe detectors hybridized with the low-noise and low-consumption ASIC IDeF-X. The 6400 detectors are operated at -20{\deg}C and reverse biased at -300 V, reaching a low energy threshold of 4 keV. The 20 us time resolution readout electronics works in photon counting mode classifying detected events as single or multiple events and measuring the deposited energy in real time. In this paper, we present the detection plane sub-systems and their main features. We also discuss its overall performances as measured both on ground and in-flight, showing compliance with the ECLAIRs science requirements.
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All authors O. Godet, J.-L. Atteia, R. Pons, C. Amoros, V. Waegebaert, K. Lacombe, P. Guillemot, B. Arcier, A. Bajat, D. Barret, L. Bouchet, J.-P. Dezalay, O. Gevin, S. Guillot, O. Limousin, S. Maestre, S. Mate, K. Mercier, G. Nasser, L. Perraud, D. Rambaud, P. Ramon, N. Remoué, M. Yassine

High Energy Astrophysical Phenomena

SVOM Science User Support at FSC

A. Claret, D. Turpin, C. Moreau et al. (+16 more)

The SVOM mission, a Sino-French collaboration dedicated to Gamma-Ray Bursts (GRBs) and transient sources, began scientific operations in 2025. This paper describes the ground computing infrastructure and user support tools for SVOM's three observing programs: the Core Program (CP), the General Program (GP), and Targets of Opportunity Program (ToO), the latter two being open to the broader scientific community, provided they collaborate with a mission Co-I. The mission adopts operational roles inspired by Swift, including on-duty scientists such as Burst Advocates (BAs), who validate GRB triggers and coordinate follow-up observations, and Instrument Scientists (IS), who calibrate and validate data for all programs. Users can access observation schedules, public data products, and support tools via the French and Chinese mission centers. The SVOM portal serves as the primary interface for accessing these resources, including a GRB public table, API, and user documentation. This paper serves as a guide for both newcomers and external researchers interested in SVOM scientific operations, focusing on aspects related to the CP.
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All authors A. Claret, D. Turpin, C. Moreau, J.-C. Thome, T. Sadibekova, F. Daigne, B. Cordier, F. Agneray, M. Brunet, N. Dagoneau, A. Formica, O. Godet, D. Gotz, H. Louvin, J. Palmerio, F. Piron, J. Rodriguez, T. Roland, K. Tazhenova

Instrumentation and Methods for Astrophysics

SVOM Science User Support Services at Chinese Science Center

Xu-hui Han, Li-ping Xin, Jing Wang et al. (+25 more)

The Chinese-French SVOM (Space-based Multi-band Astronomical Variable Objects Monitor) mission is dedicated to the study of gamma-ray bursts (GRBs) from the distant universe. A key component of the SVOM Chinese Ground Segment, the Science User Support Services (SUSS) provides comprehensive support for the mission's scientific operations. SUSS consists of two integral pillars: a suite of specialized software tools that automate key workflows, and a dedicated User Support Team that delivers expert-led, human services. These human-delivered services include operational coordination across telescope networks, direct technical assistance to astronomers, user training, and proactive problem-solving throughout the observation lifecycle. This paper focuses on the organization of SVOM scientific operations and the role of SUSS in facilitating these tasks. We provide a detailed description of the SUSS software architecture and its functionalities, encompassing the General Platform, the Burst Advocate (BA) support tools for GRB counterpart identification, the Target of Opportunity (ToO) support tools, and the General Program (GP) support tools. The structure and services provided by the user support team at the Chinese Science Center (CSC) are also elaborated. Furthermore, we evaluate the performance of SUSS during its first operational year, assessing its effectiveness in fulfilling user requirements. The evaluation offers valuable insights to guide future user support strategies and software enhancements, ultimately enabling better service for the SVOM scientific community.
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All authors Xu-hui Han, Li-ping Xin, Jing Wang, Yu-jie Xiao, Pin-pin Zhang, Ruo-song Zhang, Hong-bo Cai, Hui-jun Chen, Jin-song Deng, Wen-long Dong, Lei Huang, Lin Lan, Hua-li Li, Guang-wei Li, Xiao-meng Lu, Yu-lei Qiu, Chao Wu, Wen-jin Xie, Da-wei Xu, Jing-ran Xu, Yang Xu, Zhu-heng Yao, Mo Zhang, Xue-ying Zhao, Wei-kang Zheng, Ya-tong Zheng, Xiao-xiao Zhou, Jian-yan Wei

Instrumentation and Methods for Astrophysics

The SVOM French Science Center Infrastructure

H. Louvin, D. Corre, A. Formica et al. (+35 more)

At the heart of the SVOM French ground segment, the French Science Center is a cloud-based platform which provides services and tools for the management, storage, scientific processing and visualization of SVOM data for the French community. This digital center is a critical node of the SVOM system since it is the single point of access to SVOM scientific data for the French community and the only component of the ground system connected to the SVOM VHF network allowing near-time communication from the satellite. Scientific processing pipelines are fully integrated into its infrastructure, allowing the automated production of high-level scientific data and the generation and broadcast of alerts to the scientific community at large. The software components of the French Science Center are running 24/7 and thus require a high level of automation, which led to the development of dedicated software relying on modern technical solutions such as micro-services, application containerization, infrastructure-as-code and continuous integration and deployment. In this paper, we describe the FSC infrastructure design, technological choices, and the process of SVOM data ingestion, archiving, and automated processing by the FSC scientific pipelines. We present analysis on the FSC performances in terms of availability, amount of data processed as well as processing speed.
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All authors H. Louvin, D. Corre, A. Formica, L. Jouvin, K. Tazhenova, T. Sadibekova, J. Palmerio, N. Dagoneau, A. Sauvageon, A. Claret, F. Agneray, C. Moreau, T. Fenouillet, Y. Roehlly, J-C. Thome, L. Michel, P. Maggi, L. Kleiver, P. Maeght, U. Jacob, F. Piron, P. Bacon, N. Bellemont, C. Cavet, F. Daigne, F. Lacreu, G. Tcherniatinsky, J. Wang, Y. Canton, I. Jegouzo, N. Leroy, S. Du, S. Lion, R. Le Montagner, C. Van Hove, J. Alaux, M. Boiziot, T. Auphan

High Energy Astrophysical Phenomena

ECLAIRs: the SVOM high-energy transient trigger camera

O. Godet, J.-L. Atteia, S. Schanne et al. (+51 more)

The core instrument of the SVOM Gamma-ray burst mission launched in June 2024 is the 4-150 keV 2-D coded mask camera ECLAIRs responsible for the autonomous trigger and localization of transient events within its field of view. The flight model of ECLAIRs has been built by several French labs (IRAP, CEA, APC) under the supervision of the French Space Agency (CNES), while APC, LUPM and IAP built a suite of data reduction and analysis software. This paper outlines the main science goals of ECLAIRs and describes the different instrument sub-systems and their main characteristics. The paper then discusses the instrument configuration and operation as well as the main in-flight measured performances. Finally, the paper summarizes the science performance of ECLAIRs up to March 31, 2025.
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All authors O. Godet, J.-L. Atteia, S. Schanne, C. Lachaud, A. Goldwurm, F. Piron, Ph. Guillemot, C. Amoros, W. Bertoli, L. Bouchet, M. C. Charmeau, F. Chteau, B. Cordier, N. Dagoneau, F. Daly, J.-P. Dezalay, J. Galezzi, A. Givaudan, A. Gros, M. Karakac, K. Lacombe, H. Leprovost, S. Maestre, K. Mercier, H. Pasquier, L. Perraud, R. Pons, D. Rambaud, O. Simonella, T. Tourrette, H. Triou, V. Waegebaert, P. Bacon, T. Barlyaeva, N. Bellemont, M.-G. Bernardini, M. Brunet, F. Cangemi, C. Cavet, A. Coleiro, D. Corre, F. Daigne, A. Foisseau, O. Gevin, S. Guillot, U. Jacob, F. Lacreu, S. Le Stum, P. Maeght, T. Maiolino, A. Maolo, G. Tcherniatinksy, J. Wang, H. Yang

High Energy Astrophysical Phenomena

SVOM/VT: Instrument Overview, Science Objectives, and First-Year Performance

Yu-Lei Qiu, Li-Ping Xin, Jin-Song Deng et al. (+22 more)

The 44-cm Visible Telescope (VT) aboard the Space-based Variable Objects Monitor (SVOM) is a dual-band (400-650 nm and 650-1000 nm) instrument designed to detect and characterize the optical counterparts of gamma-ray bursts (GRBs) and other high-energy transients. This paper presents the VT's design, scientific objectives, observing strategies, and both space- and ground-based data processing pipelines, along with its first-year in-orbit performance. In-orbit commissioning tests confirm a sensitivity of 22.5 AB mag (300 s exposure), extendable to $\sim\!24$ AB mag through stacking. This performance enables the VT to monitor over 100 GRBs in its first year with an exceptional $\sim\!80\%$ detection rate for SVOM/ECLAIRS-triggered bursts and ToO-observed bursts from other missions (e.g., Swift, Fermi, Einstein Probe (EP)), outperforming Swift/UVOT's $\sim\!40\%$ detection rate. Beyond its exceptional detection efficiency, the VT played a key role in identifying high-redshift GRBs-most notably GRB 250314A (z = 7.3). Its deep upper limits at long wavelengths (up to 1 $\mu$m) were pivotal in guiding follow-up observations with large ground-based telescopes, enabling crucial near-infrared (NIR) detections. With its rapid response, deep sensitivity, and real-time processing capabilities, the VT is a key instrument for GRB research in SVOM-era, enabling critical studies of GRB optical afterglows, circumburst environments, relativistic jet dynamics, and the origins of optically dark bursts.
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All authors Yu-Lei Qiu, Li-Ping Xin, Jin-Song Deng, Jian Zhang, Xue-Wu Fan, Hong-Bo Cai, Chao Wu, Hua-Li Li, Rui-Feng Su, Qing-Yun Mao, Wei Gao, Gang-Yi Zou, Wei Wang, Zhu-Heng Yao, Dong Li, Kun Chen, Wen Chen, Yong-He Zhang, Xu-Hui Han, Jing Wang, Da-Wei Xu, Jesse T. Palmerio, Susanna. D. Vergani, Jian-Yan Wei, Bertrand Cordier

Instrumentation and Methods for Astrophysics

The data analysis pipeline for the Microchannel X-ray Telescope on board the SVOM mission

P. Maggi, L. Michel, D. Gotz et al. (+10 more)

The Space-based multi-band astronomical Variable Objects Monitor (SVOM) mission was launched in June 2024. It is a joint Sino-French collaboration designed to detect, localize, and study gammaray bursts (GRBs) and other high-energy transients. Among its onboard instruments, the Microchannel Xray Telescope (MXT) plays a central role by providing follow-up X-ray observations of GRB afterglows and other transient phenomena. To ensure timely and accurate scientific exploitation of MXT observations, a dedicated ground processing pipeline has been developed. This pipeline automatically ingests raw event lists, performs calibration, background and time filtering, corrects instrumental effects, and produces science-ready data products such as images and light curves and spectra of detected sources. In this paper, we describe the architecture and key components of the MXT data analysis pipeline, highlighting its modular design and integration within the broader SVOM ground segment. We also show results from real datasets, demonstrating the pipeline's ability to meet the performance requirements of the mission.
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All authors P. Maggi, L. Michel, D. Gotz, S. Crepaldi, A. Fort, L. Kleiver, A. Lorang, K. Mercier, M. Moita, P. Guillout, C. Motch, F. Robinet, A. Sauvageon

Instrumentation and Methods for Astrophysics

The Microchannel X-ray Telescope on board the SVOM mission: in-flight scientific performance

D. Götz, S. Crepaldi, E. Doumayrou et al. (+14 more)

The Microchannel X-ray Telescope (MXT) is a compact and lightweight focusing X-ray telescope, which is part of the space payload of the SVOM mission. The main goal of the MXT instrument is to precisely localize and physically characterize the early phases of the X-ray afterglows detected by the SVOM ECLAIRs coded mask telescope after a satellite slew. The MXT is composed by a "Lobster-Eye" type optics, with a 58$\times$58 arcmin$^{2}$ field of view, based on micro-pores of 40 $\mu$m side. This innovative type of optics is coupled to an X-ray camera, which implements at its focal plane a low-noise pnCCD. The MXT system is completed by an onboard calculator, able to command the whole telescope and to analyze in real time the MXT data stream and hence to localize the sources within the MXT field of view. In this paper, we present the MXT design and in-flight performance, as measured during the SVOM Commissioning and early science operation phase. In particular, we will focus on the optical and spectral performances, the in flight localization capabilities, and how these compare with the pre-flight ground measurements.
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All authors D. Götz, S. Crepaldi, E. Doumayrou, C. Feldman, P. Ferrando, A. Fort, H. Goto, J. Jaubert, J.-M. Le Duigou, P. Maggi, A. Meuris, M. Moita, K. Mercier, F. Robinet, C. Plasse, A. Sauvageon, C. van Hove

Instrumentation and Methods for Astrophysics

The SOXS Spectrograph Instrument Control Software

Davide Ricci, Bernardo Salasnich, Andrea Baruffolo et al. (+51 more)

SOXS (Son Of X-Shooter) is a new spectrograph for the European Southern Observatory (ESO), recently installed at the New Technology Telescope (NTT) at the La Silla Observatory, Chile. The main instrument goal consists in the characterization of transient sources, based on alerts. It covers from (partially) ultra-violet to visible and near-infrared bands, with a spectral resolution of R $\sim 4500$, using two separate, wavelength-optimized spectrographs. A scientific grade visible camera, primarily intended for target acquisition, also provides a "light imaging" mode. In this paper, we present the design of the SOXS Instrument Control Software, which is in charge of controlling all motors, calibration lamps and detectors, monitoring sensors and components' status, coordinating the execution of exposures, and implementing all observation, calibration and maintenance procedures. Given the extensive experience of the SOXS consortium in the development of instruments for the ESO Very Large Telescope (VLT), we decided to base the design of the Control System on the same standards, both for hardware and software control. We illustrate the control network, the instrument functions and detectors to be controlled, the overall design of SOXS Instrument Software (INS) and its main components. Then, we provide details about the control software for the most SOXS-specific components, and peculiar features: the piezoelectric tip-tilt corrector used for active compensation of mechanical flexures of the instrument; the cryogenic piezoelectric slit exchanger for the NIR spectrograph; the co-rotator monitoring system; and the control of the Commercial-Off-the-Shelf (COTS)- based imaging camera.
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All authors Davide Ricci, Bernardo Salasnich, Andrea Baruffolo, Jani Achrén, Matteo Aliverti, José A. Araiza-Durán, Iair Arcavi, Laura Asquini, Federico Battaini, Sagi Ben-Ami, Alex Bichkovsky, Anna Brucalassi, Rachel Bruch, Lorenzo Cabona, Sergio Campana, Giulio Capasso, Enrico Cappellaro, Riccardo Claudi, Mirko Colapietro, Rosario Cosentino, Francesco D'Alessio, Paolo D'Avanzo, Sergio D'Orsi, Massimo Della Valle, Rosario Di Benedetto, Simone Di Filippo, Avishay Gal-Yam, Matteo Genoni, Marcos Hernandez Díaz, Ofir Hershko, Jari Kotilainen, Hanindyo Kuncarayakti, Marco Landoni, Gianluca Li Causi, Laurent Marty, Seppo Mattila, Matteo Munari, Luca Oggioni, Hector Pérez Ventura, Giorgio Pariani, Giuliano Pignata, Kalyan Kumar Radhakrishnan Santhakumari, Stephen Smartt, Michael Rappaport, Marco Riva, Adam Rubin, Salvatore Savarese, Pietro Schipani, Salvatore Scuderi, Maximilian Stritzinger, Fabrizio Vitali, David Young, Ricardo Zanmar Sanchez, Gerard Zins

Cosmology and Nongalactic Astrophysics

The Three Hundred project: cosmic web identification from 2D gas and Compton-$y$ maps of galaxy clusters outskirts

Sara Santoni, Marco De Petris, Gustavo Yepes et al. (+4 more)

Galaxy clusters are located at the nodes of the filamentary network known as the cosmic web. A more comprehensive understanding of galaxy clusters can be achieved by considering their environment, in particular, the filamentary structures to which they are connected. In this work, we aim to assess the reliability of the cosmic web reconstruction from mock observational data. In particular, we aim to quantify the effects of the 2D projection relative to the underlying 3D network and the impact of using the Sunyaev-Zel'dovich (SZ) effect as a tracer of the cosmic web. We reconstruct the filamentary networks in the outskirts of The Three Hundred simulated clusters with the filament finder DisPerSE. First, we extract the networks from the 2D gas distribution and evaluate their purity and completeness with respect to the 3D networks projected along the line of sight. We also compute the distances between the corresponding skeletons. Moreover, we identify filaments from simulated Compton-$y$ maps of the clusters at redshift $z=0$, and we compare them with the 2D gas network. The skeletons extracted from 2D maps provide good representations of the underlying 3D ones, both in terms of critical points and filaments. We find a median distance between the spines of the 2D and projected 3D networks of approximately $0.22 \, h^{-1}$ Mpc, although the connectivity derived from the 2D networks is slightly underestimated. We observe a good spatial agreement between the gas and SZ networks, with a median distance of $\approx 0.24 \, h^{-1}$ Mpc. Finally, we show that gas outside galaxy clusters is preferentially located in filamentary structures, which contribute $\sim 80\%$ of the integrated Compton-$Y$ parameter of clusters' outskirts.
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All authors Sara Santoni, Marco De Petris, Gustavo Yepes, Weiguang Cui, Daniel de Andrés, Antonio Ferragamo, Raphaël Wicker

Cosmology and Nongalactic Astrophysics

The Tracking Tapered Gridded Estimator for the 21-cm power spectrum from the Murchison Widefield Array (MWA) drift scan observations – III. Improved upper limits at $z = 8.2$ from multiple pointings

Shouvik Sarkar, Khandakar Md Asif Elahi, Samir Choudhuri et al. (+5 more)

We analyze zenith-pointing $(\delta=-26.7^{\circ})$ Murchison Widefield Array (MWA) $\nu_c=154.2 \,{\rm MHz}$ drift scan observations covering $349.0^{\circ} \le \alpha \le 70.0^{\circ}$ with 163 pointing centers (PCs) spaced by $0.5^{\circ}$. We measure $D_{\ell}$, the mean-squared angular brightness temperature fluctuations, as a function of $\alpha$. A broad peak at $\alpha \approx 50.0^{\circ}$ corresponds to the bright extended source Fornax~A in the main lobe of the primary beam. A smaller peak at $\alpha \approx 5.0^{\circ}$ possibly corresponds to Fornax~A in the first sidelobe. For $\alpha \leq 22.0^{\circ}$ and $\ell \ge 200$, we find $D_{\ell} \propto \ell^2$, which we interpret as Poisson fluctuations from point sources. We present $\Delta^2(k)$, the mean-squared 21-cm brightness temperature fluctuations from the Epoch of Reionization, as a function of $\alpha$. Fornax~A causes strong contamination near $\alpha \approx 50.5^{\circ}$, elsewhere several PCs are consistent with noise. The range $358.5^{\circ} \leq \alpha \leq 11.5^{\circ}$ is relatively foreground-free and best suited for EoR science. The PC at $\alpha = 11.0^{\circ}$ yields the best $2\sigma$ upper limit $\Delta^{2}_{\rm UL}(k) = (173.13)^{2}\,{\rm mK^{2}}$ at $k = 0.161\,{\rm Mpc^{-1}}$. We incoherently combine $23$ PCs to obtain $\Delta_{\rm UL}^2(k)=(98.67)^{2}\,{\rm mK}^{2}$ at $k=0.156\,{\rm Mpc}^{-1}$. This is the tightest upper limit from the MWA, being $\approx3$ times lower than earlier MWA limits at $z = 8.2$, but $\approx2$ and $\approx21$ times higher than the LOFAR and HERA limits, respectively, and $\approx3$ orders of magnitude above theoretical predictions.
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All authors Shouvik Sarkar, Khandakar Md Asif Elahi, Samir Choudhuri, Somnath Bharadwaj, Suman Chatterjee, Baijayanta Bhattacharyya, Shiv Sethi, Akash Kumar Patwa

Solar and Stellar Astrophysics

Physical Parameters of 146 Contact Binaries Derived from Light and Radial Velocity Curves

Kai Li, Xiang Gao, Si-Rui Wang et al. (+1 more)

We present a comprehensive analysis of 146 contact binaries using medium-resolution LAMOST spectra and photometric data from the All-Sky Automated Survey for SuperNovae (ASAS-SN) and the Transiting Exoplanet Survey Satellite (TESS). Radial velocity curves obtained through the cross-correlation function method were modeled simultaneously with the light curves using the Wilson-Devinney code to derive the physical parameters of these systems. The reliability of our results was verified through comparison with previous studies of ten systems, showing good agreement. Our analysis shows that the more massive components are generally less-evolved main-sequence stars, whereas the less massive components tend to be over-sized and over-luminous, consistent with earlier findings. The distribution of orbital angular momentum supports the scenario in which contact binaries form from detached binaries via angular momentum loss. We identified 38 low mass ratio ($q < 0.25$) systems, 11 of which have extremely low mass ratios ($q < 0.15$). A remarkable example is ASASSN-V J111451.48+005038.6, which exhibits a mass ratio of 0.113 and the highest fill-out factor (98.3%) reported to date, making it a strong candidate for future mergers. Conversely, we also identified 11 high mass ratio (H-type) systems, including ASASSN-V J093921.74+390452.6 - the system with the highest spectroscopically confirmed mass ratio ($q = 0.993$) and a low fill-out factor (1.8%), suggesting it recently entered the contact phase. Additionally, several empirical relations between physical parameters are established.
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All authors Kai Li, Xiang Gao, Si-Rui Wang, Li-Heng Wang

Astrophysics of Galaxies

A Morphological Identification and Study of Radio Galaxies from LoTSS DR2. III. The Multiwavelength Analysis of Winged Radio Galaxies

Soumen Kumar Bera, Taotao Fang, Magdalena Kunert-Bajraszewska et al. (+5 more)

We present a multiwavelength follow-up study of 621 winged radio galaxies (WRGs) recently identified from LoTSS DR2, constituting the largest statistically significant samples of X-shaped (XRGs) and Z-shaped (ZRGs) radio galaxies to date. Our results show that WRGs are predominantly strongly radio-dominated, with XRGs on average more radio-luminous than ZRGs. Their optical hosts are massive elliptical galaxies residing in moderate-density environments. For 270 of XRGs, we measure angular offsets between the radio wings and the optical major axis. While most XRGs show large misalignments consistent with hydrodynamic backflow along the host minor axis, a substantial fraction ($\sim$25%) exhibits small offsets (<30{\deg}), indicating that additional processes, such as jet reorientation, may also play a role. ZRGs, in contrast, are characterized by strongly antisymmetric deformations of their radio lobes pointing toward a coherent mechanism affecting both jets, modulated by local environmental interactions at the lobe termini. Mid-infrared diagnostics indicate merger-related cold gas in many WRGs, particularly XRGs, which also more frequently host powerful AGN, while ZRGs are more often classified as low-excitation radio galaxies (LERGs). This is consistent with our previous results showing that, although most WRGs exhibit FR II morphologies, FR I sources are almost exclusively ZRGs, suggesting that Z-shaped structures are statistically associated with lower jet power and are therefore more susceptible to perturbations. Nevertheless, the physical processes responsible for shaping XRGs and ZRGs need not be fundamentally different. Instead, the final morphology likely reflects the interplay between jet power, jet stability, and the surrounding environment.
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All authors Soumen Kumar Bera, Taotao Fang, Magdalena Kunert-Bajraszewska, Tapan K. Sasmal, Si-Yue Yu, Chuan He, Xuelei Chen, Soumen Mondal

Astrophysics of Galaxies

Clash of the Trident and Tuning Fork: insights from bar and spiral strength in the (massive black hole)-stellar mass diagrams, and the `Triangal' galaxy evolution schema

Alister W. Graham

The `Triangal' galaxy evolution schema is used to assess whether the Tuning Fork (bar strength) or the van~den~Bergh Trident and ATLAS$^{3D}$ Comb (spiral strength) offer greater evolutionary insight. A new catalogue of quantitative bar strengths (measured by the bar-to-total luminosity ratio, $P$), refined galaxy morphologies, and dust bin classifications is presented. It contains 137 galaxies with spheroid stellar masses, obtained from multi-component decompositions, and directly measured black hole masses, $M_{\rm bh}$. By placing these galaxies within the $M_{\rm bh}$-($M_{\rm\star,sph}$, $M_{\rm\star,gal}$) parameter space, an evolutionary reference frame reflecting integrated growth is established. Galaxies with varying bar strengths, and double bars, are observed to not occupy preferred locations, highlighting that bars are products of secular evolution-and can be transient or recurrent phenomena-and that they track neither hierarchical mass assembly nor galaxy speciation. In contrast, three physically distinct formation channels for S0/a galaxies are identified: (primeval S0)-to-S transitions; faded spiral galaxies; and, most commonly, wet-major-merger-built dust-rich S0 galaxies (on the `green mountain'). Galaxies with particularly strong spirals appear on the right-hand side of the spiral galaxy distribution. Furthermore, a `Dust Attrition/Retention' sequence places S0 (and compact massive ES,b) galaxies with dusty nuclear discs between the dust-poor and dust-rich S0 galaxies, and a `Disc Down-sizing' sequence is revealed, in which E galaxies with dusty nuclear discs-potentially formed through `damp' mergers-bridge the ES,e (ellicular) galaxies with intermediate-scale stellar discs and the dust-poor pure E galaxies. Extensive historical context is provided, and, finally, suspected biases in precision cosmology stemming from neglected precision galaxy morphology are discussed.
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