TITLE:   GCN CIRCULAR
NUMBER:  34290
SUBJECT: GRB 230728A: Fermi GBM Observation
DATE:    23/07/28 18:51:37 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 02:50:05.24 UT on 28 July 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 230728A (trigger 712205410/230728118).
which was also detected by Swift BAT (Salvaggio et al. 2023, GCN 34282) and Swift XRT (Evans et al. 2023, GCN 34286).
The Fermi GBM on-ground location is consistent with the Swift XRT position.

The angle from the Fermi LAT boresight is 66 degrees.

The GBM light curve consists of multiple peaks with a duration (T90)
of about 19 s (50-300 keV). The time-averaged spectrum
from T0-6.1 to T0+12.3 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.2 +/- 0.2 and the cutoff energy,
parameterized as Epeak, is 95 +/- 15 keV.

The event fluence (10-1000 keV) in this time interval is
(1.7 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-2.6 s in the 10-1000 keV band is 3.1 +/- 0.2 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 78 +/- 20 keV, alpha = -1.1 +/- 0.3 and beta = -2.4 +/- 0.4.

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/"