TITLE:   GCN CIRCULAR
NUMBER:  30573
SUBJECT: GRB 210731A: Fermi GBM Observation
DATE:    21/08/01 15:26:20 GMT
FROM:    Oliver J Roberts at USRA/NASA  <oliver.roberts@nasa.gov>

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

"At 22:21:07 UT on 31 July 2021, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 210731A (trigger 649462872/210731931)
which was also detected by Swift BAT (E. Troja et al. 2021, GCN 30568).
The Fermi GBM on-ground location is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight is 102 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 26 s (10-1000 keV). The time-averaged spectrum
from T0+0.003 to T0+19.968 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.1 +/- 0.1 and the cutoff energy,
parameterized as Epeak, is 175 +/- 11 keV.

The event fluence (10-1000 keV) in this time interval is
(4.9 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+10.3 s in the 10-1000 keV band is 2.9 +/- 0.3 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/"