TITLE:   GCN CIRCULAR
NUMBER:  38507
SUBJECT: GRB 241209D: Fermi GBM Observation
DATE:    24/12/09 22:50:55 GMT
FROM:    Christian Malacaria at INAF-OAR <cmalacaria.astro@gmail.com>

C. Malacaria (INAF-OAR) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 10:59:44.09 UT on 09 December 2024, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 241209D (trigger 755434789/241209458).
which was also detected by Swift BAT (T. M. Parsotan et al. 2024, GCN 38489, 
M.R. Goad et al. 2024, GCN 38491).
The Fermi GBM on-ground location is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight is 82 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 45 s (50-300 keV). The time-averaged spectrum
from T0-0.8 to T0+44.3 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.40 +/- 0.07 and the cutoff energy,
parameterized as Epeak, is 110 +/- 3 keV.

The event fluence (10-1000 keV) in this time interval is
(9.5 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+5.9 s in the 10-1000 keV band is 4.4 +/- 0.3 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 107 +/- 4 keV, alpha = -0.35 +/- 0.08 and beta = -3.4 +/- 0.6.

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/"