{
  "subject": "GRB 250128B: Fermi GBM Observation",
  "submittedHow": "web",
  "format": "text/markdown",
  "submitter": "Ava Myers at NASA GSFC <ava.myers@nasa.gov>",
  "circularId": 39063,
  "bibcode": "2025GCN.39063....1M",
  "body": "A. Myers (NPP/GSFC) and C. Meegan (UAH) report on behalf of\nthe Fermi Gamma-ray Burst Monitor Team:\n\n\"At 16:22:53.77 UT on 28 January 2025, the Fermi Gamma-ray Burst Monitor (GBM)\ntriggered and located GRB 250128B (trigger 759774178/250128683).\nwhich was also detected by Swift BAT (P.A Evans et al. 2025, GCN [39058](https://gcn.nasa.gov/circulars/39058)).\nThe Fermi GBM on-ground location is consistent with the Swift BAT position.\n\nThe angle from the Fermi LAT boresight is 86 degrees.\n\nThe GBM light curve consists of a short single emission episode with a duration (T90)\nof about 1.1 s (50-300 keV). The time-averaged spectrum\nfrom T0-0.8 to T0+0.4 s is best fit by\na power law function with an exponential high-energy cutoff. The power law index is \n-1.0 +/- 0.5 and the cutoff energy, parameterized as Epeak, is 176 +/- 115 keV. A power law \nfunction with index -1.6 +/- 0.2 fits the spectrum equally well.\n\nThe event fluence (10-1000 keV) in this time interval is\n(2.1 +/- 0.7)E-07 erg/cm^2. The 64-ms peak photon flux measured\nstarting from T0-0.064 s in the 10-1000 keV band is 9 +/- 2 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/\"",
  "createdOn": 1738104145375,
  "eventId": "GRB 250128B"
}