TITLE: GCN CIRCULAR NUMBER: 31125 SUBJECT: GRB 211118A: Fermi GBM detection DATE: 21/11/25 15:18:49 GMT FROM: Joe Mangan at UCD J.Mangan (UCD), R. Dunwoody (UCD) and C.Meegan (UAH) report on behalf of the Fermi GBM Team: "At 23:38:14.587 UT on 18 November 2021, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 211118A (trigger 658971499 / 211118985). which was also detected by the Swift/BAT-GUANO (Raman et al. 2021, GCN 31096). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 33.7, Dec = 71.1(J2000 degrees, equivalent to J2000 02h 15m, 71d 03'), with a statistical uncertainty of 2.7 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a core-plus-tail model, with 90% of GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ) The angle from the Fermi LAT boresight at the GBM trigger time is 127 degrees. The GBM light curve consists of a single peak with a duration (T90) of about 7.2 s (50-300 keV). The time-averaged spectrum from T0-0.002 s to T0+7.776 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.21 +/- 0.07 and the cutoff energy, parameterized as Epeak, is 2176 +/- 865 keV The event fluence (10-1000 keV) in this time interval is (3.975 +/- 0.272)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.064 s in the 10-1000 keV band is 7.1 +/- 0.5 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog:https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page:https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"