{
  "submittedHow": "web",
  "createdOn": 1755810160526,
  "subject": "GRB 250821B: Fermi GBM Detection",
  "circularId": 41477,
  "bibcode": "2025GCN.41477....1S",
  "format": "text/plain",
  "eventId": "GRB 250821B",
  "body": "Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of\nthe Fermi Gamma-ray Burst Monitor Team:\n\nAt 16:07:47.46 UT on 21 August 2025, the Fermi Gamma-ray Burst Monitor (GBM)\ntriggered and located GRB 250821B (trigger 777485272/250821672).\n\nThe on-ground calculated location, using the Fermi GBM trigger data,\nis RA = 39.95, Dec = -77.13 (J2000 degrees, equivalent to\nJ2000 2h 39m, -77d 7'), with a statistical uncertainty of 1.00 degrees.\n(radius, 1-sigma containment, statistical only; there is additionally a systematic error\nwhich we have characterized as a core-plus-tail model, with 90% of GRBs having a\n3.7 deg error and a small tail suffering a larger than 10 deg systematic error\n[Connaughton et al. 2015, ApJS, 216, 32]).\n\nThe angle from the Fermi LAT boresight is 67 degrees.\n\nThe GBM light curve consists of a single emission episode with a duration (T90)\nof about 2.3 s (50-300 keV). The time-averaged spectrum\nfrom T0-0.06 to T0+2.62 s is best fit by\na Band function with Epeak = 250 +/- 10 keV,\nalpha = -0.67 +/- 0.03, and beta = -2.24 +/- 0.06.\n\nThe event fluence (10-1000 keV) in this time interval is\n(1.19 +/- 0.01)E-05 erg/cm^2. The 0.064-sec peak photon flux measured\nstarting from T0+0.576 s in the 10-1000 keV band is 58 +/- 1.9 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/",
  "submitter": "Jacob Smith at Fermi-GBM Team <jrs0118@uah.edu>"
}