TITLE:   GCN CIRCULAR
NUMBER:  31379
SUBJECT: GRB 211229B: Fermi GBM observation
DATE:    22/01/03 22:56:35 GMT
FROM:    Cori Fletcher at USRA  <cfletcher@usra.edu>

C. Fletcher (USRA) and C. Meegan (UAH) report on behalf of the Fermi GBM Team:

"At 22:18:43.10 UT on 29 December 2021, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 211229B (trigger 662509128 / 211229930)
which was also detected by the Swift/BAT-GUANO (Raman et al. 2022, GCN 31375),
GECAM (Zhao et al. 2021, GCN 31339), AGILE (Ursi et al. 2021, GCN 31344)
and INTEGRAL/SPI-ACS (#9581). The Fermi GBM Final Real-time Localization (GCN 31336)
is consistent with the GECAM position.

The angle from the Fermi LAT boresight at the GBM trigger time is 59 degrees.

The GBM light curve consists of a single peak
with a duration (T90) of about 24 s (50-300 keV).
The time-averaged spectrum from T0-15 s to T0+8.6 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.14 +/- 0.05 and
the cutoff energy, parameterized as Epeak, is 565 +/- 110 keV.

The event fluence (10-1000 keV) in this time interval is
(8.8 +/- 0.4)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.3 s in the 10-1000 keV band
is 12.4 +/- 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/"