{
  "eventId": "GRB 260921A",
  "submittedHow": "web",
  "createdOn": 1790016314538,
  "submitter": "Rushikesh Sonawane  at IISER TVM <rushikesh23@iisertvm.ac.in>",
  "circularId": 45684,
  "format": "text/plain",
  "subject": "GRB 260921A: Fermi GBM Observation",
  "body": "R. Sonawane (IISER, TVM) reports on behalf of the \nFermi Gamma-ray Burst Monitor Team:\n\n\"At 09:29:08.42 UT on 21 September 2026, the Fermi Gamma-ray Burst Monitor (GBM) \ntriggered and located GRB 260921A (trigger 811675753/260921395), \nwhich was also detected by Swift BAT (Page et al. 2026, GCN 45676).\nMASTER reported a possible optical counterpart with a candidate \nhost galaxy at z=1.3 (Lipunov et al. 2026, GCN 45678).\n\nThe Fermi GBM real-time localization (GCN 45674) is consistent with the Swift BAT position.\n\nThe angle from the Fermi LAT boresight is 95 degrees.\n\nThe GBM light curve consists of a single emission episode with a duration (T90) \nof about 17.3 s (50-300 keV). The time-averaged spectrum \nfrom T0-6.3 to T0+13.9 s is best fit by \na power law function with an exponential high-energy cutoff. \nThe power law index is -0.97 +/- 0.02 and the cutoff energy, \nparameterized as Epeak, is 280 +/- 3 keV.\n\nThe event fluence (10-1000 keV) in this time interval is \n(9.3 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured \nstarting from T0+4.0 s in the 10-1000 keV band is 12.3 +/- 0.3 ph/s/cm^2.\n\nA Band function fits the spectrum equally well \nwith Epeak = 261 +/- 3 keV, alpha = -0.95 +/- 0.01 and beta = -2.58 +/- 0.05.\n\nThe spectral analysis results presented above are preliminary; \nfinal results will be published in the GBM GRB Catalog: \nhttps://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html\n\nFor Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/\"",
  "eventType": [
    "GRB",
    "Gamma-ray Transient"
  ]
}