{
  "circularId": 44389,
  "body": "SVOM/GRM team: Hao-Xuan Guo, Chen-Wei Wang, Chao Zheng, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)\n\nSVOM/ECLAIRs team: Olivier GODET (IRAP), Frédéric Daigne (IAP)\n\nReport on behalf of the SVOM team:\n\nSVOM/GRM was triggered in-flight by GRB 260421B (SVOM trigger reference: sb26042105) at 2026-04-21T04:13:22.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44360) and SVOM/ECLAIRs (D.Zhao et al., GCN #44362).\n\nWith 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 21.5 +3.5/-2.5 s in the 15-5000 keV band.\n\nThe SVOM/GRM light curve can be found here:\nhttps://www.bursthub.cn//admin/static/svgrb260421B.png\n\nIn addition, the position of this burst, as determined by SVOM/ECLAIRs (RA = 190.0318, Dec = -17.7566, GCN #44362), is located at about 44 degrees from the SVOM optical axis, which is inside the ECLAIRs field of view.\n\nWith this localization, the time-averaged spectrum from T0-14.5 to T0+21.5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.26 +0.07/-0.06 and the cutoff energy, parameterized as Epeak, is 162 +18/-14 keV. The event fluence (10-1000 keV) in this time interval is (1.19 +/-0.05)E-05 erg/cm^2.\n\nThe 1s peak spectrum, measured from T0+14.0 to T0+15.0 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -0.72 +/-0.07 and the cutoff energy, parameterized as Epeak, is 200 +13/-12 keV. The flux (10-1000 keV) in this time interval is (2.27 +0.09/-0.08)E-06 erg/cm^2/s.\n\nWith the measured redshift z=2.115 (B. Schneider et al., GCN 44368), we calculate the isotropic energy Eiso is about 1.5E53 erg. Thus GRB 260421B is well consistent with Type II GRBs in the 'Amati' relation diagram, as shown at:\nhttps://www.bursthub.cn//admin/static/svgrb260421B_amati.png\nThe localization of GRB 260421B in the 'Yonetoku' relation diagram is shown at:\nhttps://www.bursthub.cn//admin/static/svgrb260421B_yonetoku.png\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: Hao-Xuan Guo (IHEP)(guohx@ihep.ac.cn)",
  "submittedHow": "web",
  "createdOn": 1776846660313,
  "format": "text/plain",
  "subject": "GRB 260421B: SVOM/GRM observation",
  "submitter": "guohx@ihep.ac.cn",
  "eventId": "GRB 260421B"
}