TITLE:   GCN CIRCULAR
NUMBER:  33389
SUBJECT: GRB 230228A: Fermi GBM Observation
DATE:    23/03/01 16:12:06 GMT
FROM:    Cori Fletcher at USRA  <cfletcher@usra.edu>

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

"At 05:50:51 UT on 28 February 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 230228A (trigger 699256256/230228244).
which was also detected by Swift BAT (S. Dichiara et al. 2023, GCN 33378).
The Fermi GBM on-ground location is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight is 114 degrees.

The GBM light curve consists of a single burst with a duration (T90)
of about 2 s (10-1000 keV). The time-averaged spectrum
from T0-0.9 to T0+1.5 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.8 +/- 0.3 and the cutoff energy,
parameterized as Epeak, is 110 +/- 20 keV.

The event fluence (10-1000 keV) in this time interval is
(5.9 +/- 0.6)E-07 erg/cm^2. The 64-ms peak photon flux measured
starting from T0+0 s in the 10-1000 keV band is 6 +/- 1 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/"