TITLE: GCN CIRCULAR NUMBER: 38441 SUBJECT: GRB 241204A: Fermi GBM Observation DATE: 24/12/04 21:07:30 GMT FROM: Matt Godwin msg0028@uah.edu

Matt Godwin (UAH), E. Bissaldi (Politecnico and INFN Bari), and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 03:39:22.51 UT on 04 December 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 241204A (trigger 754976367/241204152). which was also detected by Fermi-LAT (E. Bissaldi et al. 2024, GCN 38436). The Fermi GBM on-ground location is consistent with the Fermi-LAT position.

The angle from the Fermi LAT boresight is 26 degrees.

The GBM light curve consists of two peaks with a duration (T90) of about 0.8 s (50-300 keV). The time-averaged spectrum from T0-0.4 to T0+1.0 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.31 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 3453 +/- 1070 keV.

The event fluence (10-1000 keV) in this time interval is (2.22 +/- 0.09)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.64 s in the 10-1000 keV band is 41 +/- 2 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/"

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