TITLE: GCN CIRCULAR NUMBER: 40495 SUBJECT: GRB 250520A: SVOM/GRM observation DATE: 25/05/20 08:40:08 GMT FROM: Chenwei Wang at IHEP cwwang@ihep.ac.cn
SVOM/GRM team: Chen-Wei Wang, Wen-Jun Tan Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Stéphane Schanne (CEA), Marius Brunet (IRAP)
report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by a short burst GRB 250520A (SVOM trigger reference: sb25052002) at 2025-05-20T02:42:16.900 UTC (T0), which is also detected by Swift/BAT (R. A. J. Eyles-Ferris et al., GCN #40491).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 0.34 +0.12/-0.16 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250520A.png
In addition, the position of this burst, as determined by Swift (RA= 282.268, Dec=-11.847, GCN #40491), is located at about 101 degrees from the SVOM optical axis. ECLAIRs was not colecting data at the time of the burst.
With this localization, the time-averaged spectrum from T0-0.1 to T0+0.2 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.64 +/-0.13 and the cutoff energy, parameterized as Epeak, is 1080 +283/-151 keV. The event fluence (10-1000 keV) in this time interval is (2.34 +0.15/-0.14)E-06 erg/cm^2.
The localization of GRB 250505B in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/grb250520A_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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