TITLE:   GCN CIRCULAR
NUMBER:  35519
SUBJECT: GRB 240109A: Fermi GBM Observation
DATE:    24/01/11 20:28:52 GMT
FROM:    Oliver J Roberts at USRA/NASA <oliver.roberts@nasa.gov>

O.J. Roberts (USRA/NASA-MSFC) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 04:01:35.21 UT on 09 January 2024, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 240109A (trigger 726465700/240109168).
which was also detected by Swift-BAT (S. Dichiara et al. 2024, GCN 35501).
The Fermi GBM on-ground Localization is consistent with the Swift-BAT position.

The angle from the Fermi LAT boresight is 79 degrees using the Swift-BAT position.

The GBM light curve consists of a single peak with a duration (T90)
of about 0.26 s (50-300 keV). The time-averaged spectrum
from T0-0.12 to T0+0.12 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.0 +/- 0.3 and the cutoff energy,
parameterized as Epeak, is 305 +/- 179 keV.

The event fluence (10-1000 keV) in this time interval is
(1.6 +/- 0.4)E-07 erg/cm^2. The 0.064-sec peak photon flux measured
starting from T0-0.064 s in the 10-1000 keV band is 6 +/- 1 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/"