TITLE: GCN CIRCULAR NUMBER: 36218 SUBJECT: GRB 240421B: Fermi GBM Observation DATE: 24/04/21 23:05:42 GMT FROM: Cori Fletcher at USRA cfletcher@usra.edu
C. Fletcher (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 09:42:41.91 UT on 21 April 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 240421B (trigger 735385366/240421405). which was also detected by Swift BAT (M. A. Williams et al. 2024, GCN 36208). The Fermi GBM on-ground location is consistent with the Swift BAT position.
The angle from the Fermi LAT boresight is 29 degrees.
The GBM light curve consists of multiple peaks with a duration (T90) of about 12.3 s (50-300 keV). The time-averaged spectrum from T0+0.003 to T0+18.4 s is best fit by a Band function with Epeak = 141 +/- 8 keV, alpha = -0.91 +/- 0.04, and beta = -2.31 +/- 0.09.
The event fluence (10-1000 keV) in this time interval is (1.28 +/- 0.02)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+12 s in the 10-1000 keV band is 31.9 +/- 0.5 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/"
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