TITLE: GCN CIRCULAR NUMBER: 31131 SUBJECT: GRB 211120548: Fermi GBM observation DATE: 21/11/26 15:39:53 GMT FROM: Rachel Dunwoody at UCD R. Dunwoody (UCD), J.Mangan (UCD) and C.Meegan (UAH) report on behalf of the Fermi GBM Team: "At 13:09:46.84 UT on 20 November 2021, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 211120B (trigger 659106591 / 211120548). which was also detected by the Swift/BAT-GUANO (DeLaunay et al. 2021, GCN 31101) The GBM on-ground calculated location, using the GBM trigger data, is RA = 47.9, DEC = 47.1 (J2000 degrees, equivalent to 03 h 11 m, 47 d 6 '), with a statistical uncertainty of 1.9 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 62 degrees. The GBM light curve consists of a single peak with a duration (T90) of about 36.1 s (50-300 keV). The time-averaged spectrum from T0-6.400 s to T0+33.537 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.99 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 298.2 +/- 26.3 keV The event fluence (10-1000 keV) in this time interval is (1.184 +/- 0.60)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.28 s in the 10-1000 keV band is 6.5 +/- 0.2 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 180.1 +/- 24.3 keV, alpha = -0.79 +/- 0.08 and beta = -1.87 +/- 0.08. 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/"