TITLE:   GCN CIRCULAR
NUMBER:  35204
SUBJECT: GRB 231123B: Fermi GBM Observation
DATE:    23/11/27 23:30:13 GMT
FROM:    Sarah Dalessi at UAH <sd0104@uah.edu>

S. Dalessi (UAH), S. Lesage (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 19:25:21.51 UT on 23 November 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 231123B (trigger 722460326/231123809).
which was also detected by Swift/BAT-GUANO (J. DeLaunay et al. 2023, GCN 35195).
The Fermi Final Localization was reported in GCN 35170.

The angle from the Fermi LAT boresight is 104 degrees.

The GBM light curve single peak with a duration (T90)
of about 77 s (50-300 keV). The time-averaged spectrum
from T0+0.003 to T0+76.802 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 160 +/- 38 keV.

The event fluence (10-1000 keV) in this time interval is
(5.9 +/- 0.7)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+4.5 s in the 10-1000 keV band is 1.9 +/- 0.3 ph/s/cm^2.

The spectrum is also well fit a Band function with Epeak = 115 +/- 44 keV,
alpha = -1.05 +/- 0.28, and beta = -2.16 +/- 0.31.

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/"