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GCN Circular 33675

GRB 230421A: Fermi GBM observation
2023-04-22T18:20:58Z (a year ago)
Oliver J Roberts at USRA/NASA <>
E. Bissaldi (Politecnico and INFN Bari) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 09:42:46.37 UT on 21 April 2023, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 230421A (trigger 703762971 / 230421405),
which was also detected by the Swift/BAT-GUANO (DeLaunay et al. 2023, GCN 33672).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight
at the GBM trigger time is 104 degrees.

The GBM light curve consists of a single emission episode
with a duration (T90) of about 10 s (50-300 keV).
The time-averaged spectrum from T0-1 s to T0+4 s is
adequately fit by a power law function with an exponential
high-energy cutoff. The power law index is -1.1 +/- 0.2 and
the cutoff energy, parameterized as Epeak, is 360 +/- 160 keV.

The event fluence (10-1000 keV) in this time interval is
(1.3 +/- 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 3.2 +/- 0.3 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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