{
  "submitter": "Matt Godwin <msg0028@uah.edu>",
  "bibcode": "2025GCN.41876....1G",
  "eventId": "GRB 250916A",
  "body": "Matt Godwin (UAH) and C. Meegan (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:\n\n\"At 13:29:21.01 UT on 16 September 2025, the Fermi Gamma-ray Burst Monitor (GBM)\ntriggered and located GRB 250916A (trigger 779722166/250916562).\nwhich was also detected by AstroSat ( Arya et al. 2025, GCN 41843) with an optical counterpart by GOTO (Belkin et al. 2025, GCN 41847).\n\nThe angle from the Fermi LAT boresight is 66 degrees.\n\nGBM triggered on what appears to be precursor and the main emission episode begins about 150 seconds after the precursor. The lightcurve has a duration (T90)\nof about 80 s (50-300 keV). The time-averaged spectrum of the main emission\nfrom T0+230 to T0+290 s is best fit by\na Band function with Epeak = 144 +/- 9 keV,\nalpha = -1.08 +/- 0.03, and beta = -2.00 +/- 0.03.\n\nThe event fluence (10-1000 keV) within this time interval is\n(4.61 +/- 0.07)E-05 erg/cm^2. The 1-sec peak photon flux measured\nstarting from T0+270 s in the 10-1000 keV band is 5.65 +/- 0.4 ph/s/cm^2.\n\nThe time-averaged spectrum of the percursor\nfrom T0-12 to T0+05 s is best fit by\na power law function with an exponential high-energy cutoff.\nThe power law index is -0.92 +/- 0.3 and the cutoff energy,\nparameterized as Epeak, is 110 +/- 22 keV.\n\nThe event fluence (10-1000 keV) within this time interval is\n(1.31 +/- 0.15)E-05 erg/cm^2. The 1-sec peak photon flux measured\nstarting from T0+270 s in the 10-1000 keV band is 0.67 +/- 0.05 ph/s/cm^2. The localization for the preliminary pulse is uncertain,\nbut consistent with the secondary pulse.\n\nThe event fluence (10-1000 keV) within the whole time interval is\n(4.73 +/- 0.16)E-05 erg/cm^2. The 1-sec peak photon flux measured\nstarting from T0+270 s in the 10-1000 keV band is 4.57 +/- 0.3 ph/s/cm^2. The localization for the preliminary pulse is uncertain,\nbut consistent with the secondary pulse.\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/\"",
  "subject": "GRB 250916A: Fermi GBM Observation",
  "format": "text/plain",
  "circularId": 41876,
  "submittedHow": "web",
  "createdOn": 1758249799343
}