TITLE:   GCN CIRCULAR
NUMBER:  33411
SUBJECT: GRB 230307A: Fermi GBM Observation of a very bright burst
DATE:    23/03/07 22:31:41 GMT
FROM:    Sarah Dalessi at UAH  <sd0104@uah.edu>

S. Dalessi(UAH), O.J. Roberts (USRA), and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 15:44:06.67 UT on 07 March 2023, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 230307A (trigger 699896651 / 230307656). This burst
was also detected by Solar Orbiter STIX (Xiao et al. 2023, GCN 33410), and
GECAM (Xiong et al. 2023, GCN 33406). The Fermi GBM Final Real-time
Localization (GBM team 2023, GCN 33405) is consistent with the GECAM position.

The angle from the Fermi LAT boresight at the GBM trigger time is 142.0 degrees.

The GBM light curve consists of a single burst with a duration (T90)
of about 35 s (10-1000 keV). The time-averaged spectrum
from T0 to T0+148 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.07 +/- 0.01 and the cutoff energy,
parameterized as Epeak, is 936 +/- 3 keV.

The event fluence (10-1000 keV) in this time interval is
(2.951 +/- 0.004)E-03 erg/cm^2. The 1s peak photon flux measured
starting from T0+5.8 s in the 10-1000 keV band is 791 +/- 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/"