GCN Circular 35729

C. Malacaria (ISSI) reports on behalf of the Fermi GBM Team:

"At 06:19:19.82 UT on 09 February 2024, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 240209A (GCN #35712). 
A GOTO optical counterpart candidate was found 
within the GBM 90% localisation region (GCN #35715), at a nominal 
angular separation from the GBM on-ground localisation of 2.4 degrees.
Additional observations of the GOTO candidate 
were reported in GCN #35716, #35717, #35724, #35725.

Careful inspection of the GBM trigger by the Fermi-GBM Team identified 
a weak, soft GRB.
The GBM light curve consists of a single pulse with a duration (T90)
of about 5.4 s (50-300 keV). The time-averaged spectrum from 
T0-4.0 s to T0+0.0 s is best fit by a power law function with 
index of -1.82 +/- 0.07 

A power law function with an exponential high-energy cutoff with 
alpha = -1.4 +/- 0.2 and Epeak = 107 +/- 40 keV,
fits the spectrum equally well.

The event fluence (10-1000 keV) in this time interval is
(7.0 +/- 0.8)E-07 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0-1.98 s in the 10-1000 keV band
is 3.0 +/- 0.3 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."