{
  "editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Chenwei Wang at IHEP <cwwang@ihep.ac.cn>",
  "subject": "GRB 250505B: SVOM/GRM observation of a short burst",
  "body": "SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)\n\nSVOM/ECLAIRs team: Hui Yang, Laurent Bouchet (IRAP), Frédéric Piron (LUPM), Stéphane Schanne (CEA)\n\nreport on behalf of the SVOM team:\n\nSVOM/GRM was triggered in-flight by a short burst GRB 250505B at 2025-05-05T02:10:34 UTC (T0).\n\nWith the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a narrow spike followed by a tail with a T90 of 0.26 +0.13/-0.07 s in the 15-5000 keV band.\n\nThe SVOM/GRM light curve can be found here:\nhttps://www.bursthub.cn//admin/static/svgrb250505B.png\n\nThe SVOM/GRM on-ground localization of this burst is (J2000):\nRA: 55.6 deg\nDEC: -39.0 deg\nError: 4.6 deg (1sigma, statistical only)\nWe caution that the calibration of SVOM/GRM is undergoing and this localization is subject to systematic errors. \n\nIn addition, the position of this burst, as determined by GRM, is located at about 95 degrees from the SVOM optical axis. ECLAIRs was in operation during the burst but no significant signal is detected, which confirms that the burst occurred outside the ECLAIRs field of view.\n\nWith this localization, the time-averaged spectrum from T0+0.02 to T0+0.15 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.10 +0.37/-0.35 and the cutoff energy, parameterized as Epeak, is 70 +/-10 keV. The event fluence (10-1000 keV) in this time interval is (5.9 +0.6/-0.5)E-07 erg/cm^2.\n\nThe localization of GRB 250505B in the 'Amati' relation diagram is shown at: \nhttps://www.bursthub.cn//admin/static/grb250505B_amati.png\n\nWe note that the Epeak of this burst is relatively soft in short GRBs, while the hardness and duration are both similar to a magnetar X-ray burst.\n\nThe 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.\n\nThe SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang@ihep.ac.cn)\n",
  "editedOn": 1747059811033,
  "version": 2,
  "bibcode": "2025GCN.40398....1S",
  "eventId": "GRB 250505B",
  "circularId": 40398,
  "submittedHow": "web",
  "createdOn": 1746718180563,
  "format": "text/plain",
  "submitter": "Chenwei Wang at IHEP <cwwang@ihep.ac.cn>"
}