GCN Circular 35418

P. Veres (UAH), V. Sharma (NASA-GSFC/UMBC) and R. Hamburg (CNRS/IN2P3) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 07:26:02.19 UT on 22 December 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 231222B (trigger 724922767/231222310).
The GRB was also detected by Fermi LAT (Di Lalla et al, GCN 35416
Not found
 
 
).

The angle from the Fermi LAT boresight is 19 degrees.

The GBM light curve consists of two widely separated pulses with a duration (T90)
of about 121 s (50-300 keV). The time-averaged spectrum
from T0-5.1 to T0+126.0 s is best fit by
a simple power law function with index -1.55 +/- 0.04.

The event fluence (10-1000 keV) in this time interval is
(5.7 +/- 0.6)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.7 s in the 10-1000 keV band is 6.0 +/- 0.3 ph/s/cm^2.


A power law function with an exponential
high-energy cutoff fits the spectrum equally well.
The power law index is -1.09 +/- 0.16 and
the cutoff energy, parameterized as Epeak, is 257 +/- 67 keV.


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/"