GRB 251025A
GCN Circular 42441
Zhe Kang (CHO), Chao WU (NAOC), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei Qiu(NAOC), Jing Wang (NAOC), Jinsong Deng(NAOC), Lei Huang(NAOC), Jianyan Wei (NAOC), Z.M. Wang (BNU), W.J. Tan (IHEP) report on behalf of the SVOM/C-GFT team:
We observed the field of GRB 251025A (sb25102501) detected by SVOM/ECLAIRs (wang et al., GCN 42432) with LATIOS on SVOM/C-GFT. Observations started at 2025-10-25T09:36:54 UTC, ~92 seconds after the trigger.
A sequence of images in the g, r, and i bands was obtained. The likely flaring star RX J2350.0+2659, reported by Li et al. (GCN 42435), is clearly detected. The source exhibited a fade in the i band from 9.68 to 11.38 mag over ~40 min, starting around T0+93 sec. Our observations confirm that this is a stellar flare.
We thank the observation assistants Hongxu Xuan and Bowen Li at Jilin observatory for their excellent support.
The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching.
GCN Circular 42435
H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, Y. N. Ma, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, J. R. Xu, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), Z. M. Wang (BNU), W. J. Tan (IHEP) report on behalf of the SVOM/VT team.
SVOM/VT performed an automatic slew on the faint burst triggered by SVOM/ECLAIRs (sb25102501, Wang et al., GCN 42432). SVOM/VT began observing the field automatically on 2025-10-25T09:42:07, i.e., 405 sec with the slew of the platform triggered on-board, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With X band downlinked data, we find that the high proper motion star RX J2350.0+2659 was fading with the color from blue to red. It is located with a distance of 1.4 arcminutes from SVOM/MXT position (Wang et al., GCN 42432). The brightness was fading from 10.0 mag to 12.5 mag in VT_B during the first 1.6 hour after the trigger. The position of the source is consistent with XRT Source 1 (https://www.swift.ac.uk/SVOM/SVOM_FIELD00043/).
Given the fading behavior in optical and the consistency in position between VT and XRT, we propose that this event was due to a stellar flare. Our photometry was estimated in AB magnitude.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 42434
Nikos Mandarakas (LAM), Margarita Pereyra (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Z.M. Wang (BNU), W.J. Tan (IHEP):
We imaged the field of the SVOM GRB 251025A (Wang et al., GCN Circ. 42432) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-10-25 09:58 to 11:00 UTC (from 0.39 to 1.41 hours after the trigger) and obtained 47 minutes of simultaneous exposure in the r and z filters.
The data were analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
In the stacked images, we do not detect any new source within the MXT localization region (Wang et al., GCN Circ. 42432) down to the following 5-sigma limits:
r > 22.9
z > 21.7
These upper limits are consistent with the one reported by Wu et al. (GCN Circ. 42433).
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular 42433
C. Wu, H. L. Li, L. P. Xin, Y. L. Qiu (NAOC), J. Palmerio (CEA), Z. M. Wang (BNU), W. J. Tan (IHEP) report on behalf of the SVOM/VT team.
SVOM/VT began observing the field of GRB 251025A (Wang et al., GCN 42432) at 202025-10-25T09:43:10 UT, 7.8 minutes after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
No optical candidate was detected within the position of MXT (Wang et al., GCN 42432), based on a preliminary analysis of the source list and 1-bit subimage downloaded via VHF network. The 3 sigma upper limits are about 21.5 mag in VT_R with an effective exposure time of 6*50 sec at 10.3 min post trigger.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 42432
Z.M. Wang (BNU), W.J. Tan (IHEP), D. Turpin (CEA), B. Cordier(CEA), M. Moita (CEA), U. Jacob (LUPM) , report on behalf of the SVOM mission team:
At 2025-10-25T09:35:22 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251025A (SVOM burst-id sb25102501).
The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was only detected by the Image Trigger (IMT), which produced a sequence of 4 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.01 in the [5-20] keV energy band over a time window of 327.68 seconds starting at 2025-10-25T09:32:38.
The localization of the best alert is R.A., Dec. 357.5739, 27.0002 degrees (J2000) with a 90% confidence level (C.L.) radius of 9.82 arcmin (including systematic error of 2 arcmin added in quadrature).
SVOM slewed to the burst.
SVOM/MXT began observing the field at 2025-10-25T09:41:11 UTC, 349 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 357.5530, 26.9869 degrees: R.A. (J2000) = 23h50m12.72s Dec. (J2000) = 26d59m12.90s with a 90% C.L. radius of 25.08 arcseconds.
This location is 1.37 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received.
VT began observing the field after the slew. The analysis of the data will be published in a future circular.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE.
The Burst Advocate (BA) on shift for this alert is Ziming Wang: zmwang489@mail.bnu.edu.cn. Please contact the BA by email if you require additional information.