TITLE:   GCN CIRCULAR
NUMBER:  29626
SUBJECT: GRB 210308A: Fermi GBM detection
DATE:    21/03/08 20:27:21 GMT
FROM:    Stephen Lesage at Fermi-GBM Team  <sjl0014@uah.edu>

S. Lesage (UAH), A. von Kienlin (MPE), C. Meegan (UAH), and C. Malacaria
(NASA-MSFC/USRA)
report on behalf of the Fermi GBM Team:

"At 06:37:56.91 UT on 08 March 2021, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 210308A (trigger 636878281 / 210308276)
which was also detected by the Swift/BAT and Swift/XRT
(D'Elia et al. 2021, GCN 29619).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 26
degrees.

The GBM light curve shows a single-peaked structure
with a duration (T90) of about 5.4 s (50-300 keV).
The time-averaged spectrum from T0-1.7 s to T0+7.5 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -0.82 +/- 0.04 and
the cutoff energy, parameterized as Epeak, is 142 +/- 5 keV.
A Band function fits the spectrum equally well with
Epeak = 135 +/- 7 keV, alpha = -0.78 +/- 0.05 and beta = -3.0 +/- 0.4.

The event fluence (10-1000 keV) in this time interval is
(6.3 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+2.1 s in the 10-1000 keV band
is 20.0 +/- 0.4 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/"