TITLE:   GCN CIRCULAR
NUMBER:  37239
SUBJECT: GRB 240821A: Fermi GBM Observation
DATE:    24/08/22 21:09:30 GMT
FROM:    Sarah Dalessi at UAH <sd0104@uah.edu>

S. Dalessi (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 18:36:02.60 UT on 21 August 2024, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 240821A (trigger 745958167/240821775).
which was also detected by SVOM (F. Cangemi et al. 2024 GCN 37220, J. He et al. 2024 37226) and EIRSAT-1 (D. Murphy et al. 2024, GCN 37232).
The Fermi GBM on-ground location is consistent with the SVOM position.

The angle from the Fermi LAT boresight is 89 degrees.

The GBM light curve single emission episode with a duration (T90)
of about 1.9 s (50-300 keV). The time-averaged spectrum
from T0-0.2 to T0+2.9 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.93 +/- 0.06 and the cutoff energy,
parameterized as Epeak, is 370 +/- 40 keV.

The event fluence (10-1000 keV) in this time interval is
(3.9 +/- 0.2)E-06 erg/cm^2. The 64-ms peak photon flux measured
starting from T0+0.64 s in the 10-1000 keV band is 28 +/- 2 ph/s/cm^2.

A Band function fits the spectrum equally well with Epeak= 238 +/- 42 keV, alpha = -0.74 +/- 0.11 and beta = -1.96 +/- 0.11.

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/"