TITLE:   GCN CIRCULAR
NUMBER:  33324
SUBJECT: GRB 230209B: Fermi GBM Observation
DATE:    23/02/14 21:51:53 GMT
FROM:    Sarah Dalessi at UAH  <sd0104@uah.edu>

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

"At 22:32:36.89 UT on 09 February 2023, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 230209B (trigger 697674761 / 230209939)
which was also detected by the Swift/BAT-GUANO (G. Raman et al. 2023,
GCN 33315).
The Fermi GBM Final Real-time Localization (GCN #33310) is consistent with the
localization by the IPN network (Kozyrev et al. 2023, GCN 33323).

The angle from the Fermi LAT boresight at the GBM trigger time is 76 degrees.

The GBM light curve consists of multiple peaks
with a duration (T90) of about 67 s (50-300 keV).
The time-averaged spectrum from T0-2.82 s to T0+68.87 s is best fit by
a Band function with Epeak = 183 +/- 6 keV,
alpha = -0.34 +/- 0.04, and beta = -2.44 +/- 0.09.

The event fluence (10-1000 keV) in this time interval is
(3.669 +/- 0.052)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.83 s in the 10-1000 keV band
is 16.4 +/- 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/"