TITLE: GCN CIRCULAR NUMBER: 40625 SUBJECT: GRB 250530A: SVOM/GRM analysis DATE: 25/06/04 03:52:55 GMT FROM: Chenwei Wang at IHEP cwwang@ihep.ac.cn
SVOM/GRM team: Chen-Wei Wang, Chao Zheng, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: M. G. Bernardini (INAF-OAB, LUPM)
Report on behalf of the SVOM team:
SVOM/GRM detected the burst GRB 250530A at 2025-05-30T06:31:54.99 UTC (T0), which is also detected by SVOM/ECLAIRs (Wang et al., GCN #40576).
With the event-by-event data downloaded through the X-band ground station, we conducted the standard analysis pipeline of GRB 250530A. The GRM light curve shows that this burst consists of a single pulse with a T90 of 15.0 +3.0/-4.0 s in the 15-5000 keV band, which is consistent with the result from VHF data.
With the localization of ECLAIRs (RA=186.71, DEC=-2.5648), the time-averaged spectrum from T0 to T0+15 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.26 +0.18/-0.13 and the cutoff energy, parameterized as Epeak, is 707 +1140/-360 keV. The event fluence (10-1000 keV) in this time interval is (2.8 +/-0.4)E-06 erg/cm^2.
Thus GRB 250530A is consistent with Type I GRBs in the 'Amati' relation diagram although the duration is much longer than 2 seconds, as shown at: https://www.bursthub.cn//admin/static/grb250530A_amati.png Further follow-up observations are encouraged.
We note that the calibration of SVOM/GRM is undergoing thus these results are preliminary. Refined analysis will be reported later.
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: Chen-Wei Wang (IHEP) (cwwang@ihep.ac.cn)
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