TITLE: GCN CIRCULAR NUMBER: 42184 SUBJECT: GRB 251007A: SVOM/GRM observation DATE: 25/10/10 12:47:58 GMT FROM: yzh807926@163.com
SVOM/GRM team: Zheng-Hang Yu, Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Feliu Lacreu (IAP), Sebastien Guillot (IRAP), Olivier GODET (IRAP), Marius Brunet (IRAP), Frédéric Piron (LUPM), Jean-Luc Atteia (IRAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by a burst GRB 251007A (SVOM trigger reference: sb25100703) at 2025-10-07T19:37:53.000 UTC (T0), which is also detected by Swift/BAT (Ambrosi et al. 2025, GCN #42146), Glowbug (Cheung et al. 2025, GCN #42151) and CALET/GBM (A. Yoshida et al. 2025, GCN #42156).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a precursor followed by a main episode with multiple peaks a T90 of 58.0 +1.5/-5.5 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251007A.png
In addition, the position of this burst, as determined by Swift/BAT (RA= 128.1775, DEC= 21.8138, GCN#42146), is located at about 49 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. Nevertheless, ECLAIRs detected the burst above 50 keV through its shield.
With this localization, the time-averaged spectrum from T0-50 to T0+30 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.27 +0.04/-0.04 and the cutoff energy, parameterized as Epeak, is 761 +219/-152 keV. The event fluence (10-1000 keV) in this time interval is (3.97 +0.14/-0.15)E-05 erg/cm^2.
The localization of GRB 251007A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251007A_amati.png
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 point of contact for this burst is: Zheng-Hang Yu(IHEP)(zhyu@ihep.ac.cn)
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