TITLE:   GCN CIRCULAR
NUMBER:  35632
SUBJECT: GRB 240123B: Fermi GBM Observation
DATE:    24/01/25 19:45:45 GMT
FROM:    Lorenzo Scotton at UAH <lscottongcn@outlook.com>

L. Scotton (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 17:48:03.22 UT on 23 January 2024, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 240123B (trigger 727724888/240123742).
which was also detected by Swift/BAT-GUANO (Ronchini et al. 2024, GCN 35629).
The Fermi GBM Final Real-time Localization was reported in GCN 35608.

The angle from the Fermi LAT boresight is 51 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 12 s (50-300 keV). The time-averaged spectrum
from T0-0.5 to T0+11.5 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.6 +/- 0.2 and the cutoff energy,
parameterized as Epeak, is 250 +/- 30 keV.

The event fluence (10-1000 keV) in this time interval is
(2.6 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+4.9 s in the 10-1000 keV band is 2.4 +/- 0.2 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 130 +/- 30 keV, alpha = 0.1 +/- 0.4 and beta = -1.9 +/- 0.1.

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/"