TITLE:   GCN CIRCULAR
NUMBER:  33146
SUBJECT: GRB 221231A: Fermi GBM Observation
DATE:    23/01/04 05:01:54 GMT
FROM:    Stephen Lesage at Fermi-GBM Team  <sjl0014@uah.edu>

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

"At 21:46:05 UT on 31 December 2022, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 221231A (trigger 694215970/221231907).
which was also detected by Swift BAT (A. Tohuvavohu et al. 2023, GCN 33132)
and Swift XRT GCN (M. Perri et al. 2023, 33139).
The Fermi GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight is 61 degrees.

The GBM light curve consists of a single emission episode with a duration
(T90)
of about 5 s (50-300 keV). The time-averaged spectrum
from T0-0.06 to T0+4.93 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.2 +/- 0.4 and the cutoff energy,
parameterized as Epeak, is 200 +/- 40 keV.

The event fluence (10-1000 keV) in this time interval is
(4.4 +/- 0.4)E-07 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0 s in the 10-1000 keV band is 3.9 +/- 0.2 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/"