GCN Circular 34689
S. Dalessi (UAH), R. Hamburg (CNRS/IJCLab), and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 07:56:12.16 UT on 13 September 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 230913A (trigger 716284577/230913331). which was also detected by Swift/BAT GUANO (S. Ronchini et al. 2023, GCN 34683). The Fermi GBM Final Real-time Localization was reported in GCN 34680. The angle from the Fermi LAT boresight is 41 degrees. The GBM light curve single peak with a duration (T90) of about 12 s (50-300 keV). The time-averaged spectrum from T0-1.0 to T0+9.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.1 +/- 0.2 and the cutoff energy, parameterized as Epeak, is 160 +/- 10 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+1.3 s in the 10-1000 keV band is 2.1 +/- 0.2 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 130 +/- 20 keV, alpha = 0.3 +/- 0.4 and beta = -2.3 +/- 0.2. 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/"