TITLE:   GCN CIRCULAR
NUMBER:  33531
SUBJECT: GRB 230328B: Fermi GBM observation
DATE:    23/03/28 22:50:25 GMT
FROM:    Sarah Dalessi at UAH  <sd0104@uah.edu>

S. Dalessi (UAH) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 14:54:47.43 UT on 28 March 2023, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 230328B (trigger 701708092 / 230328621),
which was also detected by the Swift/BAT (J.D. Gropp et al. 2023, GCN 33527)
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 38 degrees.

The GBM light curve consists of a single burst
with a duration (T90) of about 19 s (50-300 keV).
The time-averaged spectrum from T0-3.5 s to T0+19.1 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.16 +/- 0.03 and
the cutoff energy, parameterized as Epeak, is 169.6 +/- 9.9 keV.

The event fluence (10-1000 keV) in this time interval is
(9.4 +/- 0.3)E-06 erg/cm^2. The 1 sec peak photon flux measured
starting from T0+1.4 s in the 10-1000 keV band
is 12.7 +/- 0.3 ph/s/cm^2.

A Band function fits the spectrum equally well with Epeak = 125.0 +/- 11.3 keV,
alpha = -1.03 +/- 0.06, and beta = -2.10+/- 0.09.

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/"