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GCN Circular 33828

GRB 230518A: Fermi GBM Observation
2023-05-19T17:07:45Z (20 days ago)
S. Bala (USRA), C. Fletcher (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 22:49:27.61 UT on 18 May 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 230518A (trigger 706142972/230518951). which was also detected by Swift/BAT-GUANO (S. Ronchini et al. 2023, GCN 33825). The Fermi GBM Final Real-time Localization was reported in GCN 33822. The angle from the Fermi LAT boresight is 23 degrees. The GBM light curve consists of one short peak with a duration (T90) of about 0.9 s (50-300 keV). The time-averaged spectrum from T0-0.7 to T0+0.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is 0.6 +/- 0.7 and the cutoff energy, parameterized as Epeak, is 503 +/- 138 keV. The event fluence (10-1000 keV) in this time interval is (5.5 +/- 0.9)E-07 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.0 s in the 10-1000 keV band is 4 +/- 1 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: For Fermi GBM data and info, please visit the official Fermi GBM Support Page:"
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