TITLE: GCN CIRCULAR NUMBER: 33755 SUBJECT: GRB 230506C: Fermi GBM detection DATE: 23/05/10 17:37:35 GMT FROM: Suraj Poolakkil at UAH S. Poolakkil (UAH) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 17:09:16.97 UT on 6 May 2023, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 230506C (trigger 705085761 / 230506715) which was also detected by the Swift/BAT (Tohuvavohu et al. 2023, GCN 33731). The angle from the Fermi LAT boresight at the GBM trigger time is 15 degrees. The GBM light curve consists of a single peak followed by some extended emission with a duration (T90) of about 23 s (50-300 keV). The time-averaged spectrum from T0-6.1 s to T0+11.3 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.19 +/- 0.11 and the cutoff energy, parameterized as Epeak, is 163 +/- 30 keV. The event fluence (10-1000 keV) in this time interval is (3.1 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+3.0 s in the 10-1000 keV band is 3.3 +/- 0.2 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/"