GCN Circular 33675
E. Bissaldi (Politecnico and INFN Bari) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 09:42:46.37 UT on 21 April 2023, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 230421A (trigger 703762971 / 230421405), which was also detected by the Swift/BAT-GUANO (DeLaunay et al. 2023, GCN 33672). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 104 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 10 s (50-300 keV). The time-averaged spectrum from T0-1 s to T0+4 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -1.1 +/- 0.2 and the cutoff energy, parameterized as Epeak, is 360 +/- 160 keV. The event fluence (10-1000 keV) in this time interval is (1.3 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.3 s in the 10-1000 keV band is 3.2 +/- 0.3 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/"