{
  "submitter": "oindabimukherjee@gmail.com",
  "createdOn": 1776800176903,
  "circularId": 44382,
  "subject": "GRB 260421B: Fermi GBM Observation",
  "submittedHow": "web",
  "body": "O. Mukherjee (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:\n\n\"At 04:13:21.17 UT on 21 April 2026, the Fermi Gamma-ray Burst Monitor (GBM)\ntriggered and located GRB 260421B (trigger 798437606/260421176),\nwhich was also detected by SVOM/ECLAIRs (Zhao et al. 2026, GCN 44362),\nand VLT/X-shooter with spectroscopic redshift z = 2.115 (Schneider et al. 2026, GCN 44368).\nThe Fermi GBM on-ground location (GCN 44360) is consistent with the SVOM/ECLAIRs position.\n\nThe angle from the Fermi LAT boresight is 58 degrees.\n\nThe GBM light curve consists of a single emission episode with a duration (T90)\nof about 18 s (50-300 keV). The time-averaged spectrum\nfrom T0-1.6 to T0+24.9 s is best fit by\na power law function with an exponential high-energy cutoff.\nThe power law index is -1.11 +/- 0.01 and the cutoff energy,\nparameterized as Epeak, is 159 +/- 1 keV.\n\nThe event fluence (10-1000 keV) in this time interval is\n(1.06 +/- 0.01)E-05 erg/cm^2. The 1-sec peak photon flux measured\nstarting from T0+15 s in the 10-1000 keV band is 15.4 +/- 0.3 ph/s/cm^2.\n\nA Band function fits the spectrum equally well\nwith Epeak= 130 +/- 1 keV, alpha = -1 +/- 0.005 and beta = -2.31 +/- 0.02.\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:\nhttps://fermi.gsfc.nasa.gov/ssc/data/access/gbm/\"",
  "format": "text/plain",
  "eventId": "GRB 260421B"
}