GCN Circular 30253
J. Wood (NASA/MSFC) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 01:43:36.14 UT on 18 June 2021, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 210618A (trigger 645673421 / 210618072) which was also detected by the Swift/BAT (M. G. Bernardini et al. 2019, GCN 30250). The Fermi GBM Final Real-time Localization (GCN 30248) is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 113 degrees. The GBM light curve consists of multiple peaks with a duration (T90) of about 3.6 s (50-300 keV). The time-averaged spectrum from T0-1.6 s to T0+2.2 s is well fit by a power law function with an exponential high-energy cutoff. The power law index is -0.62 +/- 0.26 and the cutoff energy, parameterized as Epeak, is 440 +/- 140 keV The event fluence (10-1000 keV) in this time interval is (1.2 +/- 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 2.1 +/- 0.3 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 400 +/- 190 keV, alpha = -0.60 +/- 0.32 and beta = -2.3 +/- 0.9. 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/"