{
  "submittedHow": "web",
  "bibcode": "2025GCN.41376....1S",
  "subject": "GRB 250813B: Fermi GBM Observation",
  "createdOn": 1755199031968,
  "eventId": "GRB 250813B",
  "body": "Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of\nthe Fermi Gamma-ray Burst Monitor Team:\n\nAt 22:51:11.24 UT on 13 August 2025, the Fermi Gamma-ray Burst Monitor (GBM)\ntriggered and located GRB 250813B (trigger 776818276/250813952), which was also detected by SVOM/ECLAIRs (W.J. Xie, et al. 2025, GCN 41354).\nThe Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position.\n\nAn optical afterglow was first reported by Ondrejov D50 (M. Jelinek, et al. 2025, GCN 41353) which also reports an extremely rapid decay (M. Jelinek, et al. 2025, GCN 41355). \nA redshift of z=1.752 was report by the VLT (B. Schneider, et al. 2025, GCN 41363).\n\nThe angle from the Fermi LAT boresight is 99 degrees.\n\nThe GBM light curve consists of multiple emission episodes with a duration (T90)\nof about 24.1 s (50-300 keV). The time-averaged spectrum\nfrom T0-3.8 to T0+31.0 s is best fit by\na power law function with an exponential high-energy cutoff.\nThe power law index is -0.82 +/- 0.04 and the cutoff energy,\nparameterized as Epeak, is 114 +/- 3 keV. A Band function fits equally well with Epeak = 112 +/- 4, alpha = -0.81 +/- 0.04, and beta = -3.67 +/- 0.79.\n\nThe event fluence (10-1000 keV) in this time interval is\n(1.30 +/- 0.02)E-05 erg/cm^2. The 1-sec peak photon flux measured\nstarting from T0+11 s in the 10-1000 keV band is 8.1 +/- 0.3 ph/s/cm^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/",
  "circularId": 41376,
  "format": "text/plain",
  "submitter": "Jacob Smith at Fermi-GBM Team <jrs0118@uah.edu>"
}