TITLE:   GCN CIRCULAR
NUMBER:  35860
SUBJECT: GRB 240303B: Fermi GBM Detection
DATE:    24/03/04 15:41:29 GMT
FROM:    rachel.hamburg@ijclab.in2p3.fr

R. Hamburg (CNRS/IN2P3/IJCLab) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 12:18:51.24 UT on 03 March 2024, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 240303B (trigger 731161136 / 240303513).
The on-ground calculated location is reported in GCN 35850.
This burst was also detected by CALET (Nakahira et al., 2024; GCN 35857)
and the INTEGRAL SPI-ACS (trigger 10612).

The angle from the Fermi LAT boresight is 96 degrees.

The GBM light curve consists of a single bright pulse with a duration (T90)
of about 5.9 s (50-300 keV). The time-averaged spectrum
from T0-1.0 to T0+8.2 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.33 +/- 0.03 and the cutoff energy,
parameterized as Epeak, is 540 +/- 20 keV.
A Band function fits the spectrum equally well
with Epeak= 510 +/- 20 keV, alpha = -0.30 +/- 0.04 and beta = -3 +/- 0.3.

The event fluence (10-1000 keV) in this time interval is
(2.31 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.9 s in the 10-1000 keV band is 18.5 +/- 0.3 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/"