TITLE: GCN CIRCULAR NUMBER: 33766 SUBJECT: GRB 230510A: Fermi GBM detection DATE: 23/05/11 08:36:05 GMT FROM: R. Hamburg at CNRS/IJCLab C. Malacaria (ISSI) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 12:04:06.93 UT on 10 April 2023, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 230510A (trigger 705413051 / 230510503), which was also detected by the Swift/BAT and Swift/XRT (Eyles-Ferris et al. 2023, GCN 33752; Evans et al. 2023, GCN 33756). The GBM on-ground location is consistent with the Swift position (GCN 33751). The angle from the Fermi LAT boresight at the GBM trigger time is 14 degrees. The GBM light curve shows a weaker peak followed about 100 s later by a brighter peak, with a duration (T90) of about 177 s (50-300 keV). The time-averaged spectrum from T0-4.1 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 -0.9 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 87 +/- 7 keV. A Band function fits the spectrum equally well with Epeak = 87 +/- 9 keV, alpha = -0.9 +/- 0.1 and beta = -3.8 +/- 3.2. The event fluence (10-1000 keV) in this time interval is (2.0 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+158 s in the 10-1000 keV band is 12.4 +/- 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/"