TITLE: GCN CIRCULAR NUMBER: 36535 SUBJECT: GRB 240521B: Fermi GBM Observation DATE: 24/05/23 01:21:12 GMT FROM: Sarah Dalessi at UAH <sd0104@uah.edu> S. Dalessi (UAH), C. Fletcher (USRA), and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 15:08:57.06 UT on 21 May 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 240521B (trigger 737996942/240521631). which was also detected by Swift/BAT-GUANO (Ronchini et al. 2024, GCN 36532). The Fermi GBM on-ground location is consistent with the Swift/BAT-GUANO position. The angle from the Fermi LAT boresight is 101 degrees. The GBM light curve single emission episode with a duration (T90) of about 34 s (50-300 keV). The time-averaged spectrum from T0-16 to T0+17 s is best fit by a simple power law function with index -1.64 +/- 0.04. The event fluence (10-1000 keV) in this time interval is (4 +/- 0.5)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-9.9 s in the 10-1000 keV band is 4.1 +/- 0.4 ph/s/cm^2. A power law function with an exponential high-energy cutoff fits the spectrum equally well. The power law index is -1.48 +/- 0.11 and the cutoff energy, parameterized as Epeak, is 222 +/- 94 keV. 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/" View this GCN Circular online at https://gcn.nasa.gov/circulars/36535. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...