TITLE: GCN CIRCULAR NUMBER: 41283 SUBJECT: GRB 250807A: SVOM/GRM observation DATE: 25/08/08 11:07:22 GMT FROM: Chenwei Wang at IHEP cwwang@ihep.ac.cn
SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Sebastien Guillot (IRAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by GRB 250807A (SVOM trigger reference: sb25080702) at 2025-08-07T10:46:06.700 UTC (T0), which is also detected by Swift/BAT (N. J. Klingler et al., GCN #41262), AstroSat (S.Salunke et al., GCN #41281) and Konus-Wind.
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 71.0 +4.5/-7.0 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250807A.png
In addition, the position of this burst, as determined by Swift/BAT (RA= 51.420, DEC= -47.877, GCN #41064), is located at about 69 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. Nonetheless, the burst is seen (via analysis of X-band data) in the ECLAIRs data above 50 keV at the T0 given by GRM, likely through the ECLAIRs shielding.
With this localization, the time-averaged spectrum from T0-15 to T0+130 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.19 +/-0.03 and the cutoff energy, parameterized as Epeak, is 547 +52/-45 keV. The event fluence (10-1000 keV) in this time interval is (1.00 +/-0.10)E-04 erg/cm^2. Thus GRB 250807A is consistent with Type II GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/grb250807A_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: Chen-Wei Wang (IHEP)(cwwang@ihep.ac.cn)
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