TITLE: GCN CIRCULAR NUMBER: 31689 SUBJECT: GRB 220305A: Fermi GBM observation DATE: 22/03/05 23:40:22 GMT FROM: Joe Mangan at UCD R. Dunwoody (UCD), J. Mangan (UCD) and C.Meegan (UAH) report on behalf of the Fermi GBM Team: "At 11:33:20.48 UT on 05 March 2022, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 220305A (trigger 668172805 / 220305481). The on-ground calculated location, using the GBM trigger data, is RA = 174, DEC = -34 (J2000 degrees, equivalent to 11 h 36 m, -34 d 00 '), with a statistical uncertainty of 1.5 degrees. The angle from the Fermi LAT boresight at the GBM trigger time is 35 degrees. The GBM light curve consists of three emission episodes, the most prominent occurring around T0+50s, with a duration (T90) of about 172.8 s (50-300 keV). The time-averaged spectrum for the first emission episode, from T0-12.3 to T0+12.3, is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.6 +/- 0.5 and the cutoff energy, parameterized as Epeak, is 60.9 +/- 9.1 keV. The event fluence (10-1000 keV) in this time interval is (6.8 +/- 0.8)E-07 erg/cm^2. The time-averaged spectrum for the second emission episode, from T0+39.9 to T0+60.4, is best fit by a Band function with Epeak = 320.7 +/- 35.7 keV, alpha = -0.9 +/- 0.1, and beta = -1.9 +/- 0.1. The event fluence (10-1000 keV) in this time interval is (1.78 +/- 0.03)E-05. The time-averaged spectrum for the third emission episode, from T0+164.9 to T0+193.5, is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.3 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 205.2 +/- 42.8 keV. The event fluence (10-1000 keV) in this time interval is(3.5 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+49.6 s in the 10-1000 keV band is 19.5 +/- 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/"