TITLE: GCN CIRCULAR NUMBER: 39813 SUBJECT: GRB 250320B: SVOM/GRM observation of a long burst DATE: 25/03/21 13:20:50 GMT FROM: wenlongzhang2018@163.com
SVOM/GRM team: Wen-Long Zhang, Wen-Jun Tan, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Nicolas Dagoneau (CEA), Maria-Grazia Bernardini (INAF-OAB), Jean-Luc Atteia (IRAP), Frédéric Piron (LUPM)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by GRB 250320B (SVOM trigger reference: sb25032001) at 2025-03-20T23:15:23.000 (T0), which was also observed by Fermi/GBM (Fermi GBM team, GCN #39792) and AstroSat CZTI (J. Joshi et al., GCN 39808).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-peaks with a T90 of 86.5 +0.5/-1.0 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250320B.png
In addition, the position of this burst, as determined by Fermi/GBM (Fermi GBM Team, GCN #39792), is located at about 53.9 degrees (with a few degrees of statistical and systematic errors) from the SVOM optical axis. This burst was detected by the Count-Rate Trigger onboard ECLAIRs, as an increase in counts over background, but it was not localized by the coded-mask imaging process, which confirms that the burst occurred outside the ECLAIRs field of view.
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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.
The SVOM/GRM point of contact for this burst is: Wen-Long Zhang (IHEP) (zhangwl@ihep.ac.cn)
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