{
  "createdOn": 1781890770516,
  "format": "text/plain",
  "circularId": 45010,
  "eventId": "GRB 260618B",
  "submittedHow": "web",
  "body": "P. Veres (UAH) and C. Meegan (UAH) report on behalf of\nthe Fermi Gamma-ray Burst Monitor Team:\n\n\"At 16:55:04.71 UT on 18 June 2026, the Fermi Gamma-ray Burst Monitor (GBM)\ntriggered and located GRB 260618B (trigger 803494509/260618705),\nwhich was also detected by Fermi/LAT (Gupta et al., GCN 44983) and SVOM/VT (Li et al., GCN 45001).\nThe Fermi GBM on-ground location is consistent with the LAT and the SVOM/VT position.\n\nThe angle from the Fermi LAT boresight is 16 degrees.\n\nThe GBM light curve consists of a single emission episode with a duration (T90)\nof about 20 s (50-300 keV). The time-averaged spectrum\nfrom T0 to T0+10 s is best fit by\na power law function with an exponential high-energy cutoff.\nThe power law index is -0.42 +/- 0.01 and the cutoff energy,\nparameterized as Epeak, is 1030 +/- 20 keV.\n\nThe event fluence (10-1000 keV) in this time interval is\n(9.4 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured\nstarting from T0+0.96 s in the 10-1000 keV band is 4.3 +/- 0.2 ph/s/cm^2.\n\nA Band function fits the spectrum equally well\nwith Epeak= 1000 +/- 20 keV, alpha = -0.41 +/- 0.02 and beta = -3.2 +/- 0.2.\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/\"",
  "bibcode": "2026GCN.45010....1V",
  "submitter": "Peter Veres at University of Alabama in Huntsville <veresp@gmail.com>",
  "subject": "GRB 260618B: Fermi GBM Observation"
}