TITLE:   GCN CIRCULAR
NUMBER:  33288
SUBJECT: GRB 230204B: Fermi GBM detection
DATE:    23/02/06 20:28:18 GMT
FROM:    Suraj Poolakkil at UAH  <sp0076@uah.edu>

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

"At 21:44:27.20 UT on 4 February 2023, the Fermi Gamma-Ray Burst Monitor
(GBM)
triggered and located GRB 230204B (trigger 697239872 / 230204906)
which was also detected by the Swift/BAT-GUANO (Kennea et al. 2023, GCN
33267),
Swift-XRT (D'Elia et al. 2023, GCN 33285), MAXI/GS (Serino et al. 2023, GCN
33265),
AGILE (Casentini et al. 2023, GCN 33272), ATLAS (Smartt et al. 2023, GCN
33278),
and VLT/X-shooter (Saccardi et al. 2023, GCN 33281).

The angle from the Fermi LAT boresight at the GBM trigger time is 106
degrees.

The GBM light curve consists of multiple peaks followed
by some extended emission with a duration (T90) of about 216 s (50-300 keV).
The time-averaged spectrum from T0-1.024 s to T0+228.4 s
is best fit by a power law function with an exponential
high-energy cutoff. The power law index is -0.97 +/- 0.02  and
the cutoff energy, parameterized as Epeak, is 783 +/- 40 keV.
A Band function fits equally well, with Epeak = 763 +/- 45 keV,
alpha = -0.97 +/- 0.02 and beta = -2.73 +/- 0.29.

The event fluence (10-1000 keV) in this time interval is
(138.9 +/- 1.5)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+156 s in the 10-1000 keV band
is 7.3 +/- 0.4 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/"