TITLE: GCN CIRCULAR NUMBER: 32574 SUBJECT: GRB 220921A: Fermi GBM detection DATE: 22/09/22 17:01:16 GMT FROM: Elisabetta Bissaldi at INFN,Bari E. Bissaldi (Politecnico and INFN Bari) reports on behalf of the Fermi GBM Team: "At 11:05:59.071 UT on 21 September 2022, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 220921A (trigger 685451164/ 220921462), which was also detected by Fermi-LAT (Pillera et al. 2022, GCN #32568). The on-ground calculated location, using the GBM trigger data, is RA = 66.85, DEC = -40.0 (J2000 degrees, equivalent to 04h 27m, -40d 00'), with a statistical uncertainty of 1 degree (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 Fermi GBM on-ground Localization is consistent with the Fermi-LAT position. The angle from the Fermi LAT boresight at the GBM trigger time is 69 degrees. The GBM light curve consists of multiple emission episodes with a duration (T90) of about 210 s (50-300 keV). The time-averaged spectrum from T0 to T0+40 s is best fit by a Band function with Epeak = 142 +/- 4 keV, alpha = -0.90 +/- 0.02, and beta = -2.09 +/- 0.02. The event fluence (10-1000 keV) in this time interval is (5.92 +/- 0.04)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+11 s in the 10-1000 keV band is 36.2 +/- 0.4 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/"