TITLE: GCN CIRCULAR NUMBER: 38561 SUBJECT: GRB 241212A: Fermi GBM detection DATE: 24/12/13 15:43:11 GMT FROM: Joe Mangan at IJCLab joseph.mangan@ijclab.in2p3.fr

J. Mangan (CNRS/IJCLab) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 09:21:48.66 UT on 12 December 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 241212A (trigger 755688113 / 241212390), which was also detected by, SVOM-GRM (Zhang Li et al. 2024, GCN 38541), and for which there is a possible optical counterpart (P.A. Evans et al. 2024, GCN 38559).

The Fermi GBM Final Real-time Localization is reported in GCN 38540. The angle from the Fermi LAT boresight at the GBM trigger time is 40 degrees.

The GBM light curve consists of a single emission with a duration (T90) of about 39 s (50-300 keV). The time-averaged spectrum from T0-0 s to T0+34 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.1 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 304.8 +/- 59.1 keV. The event fluence (10-1000 keV) in this time interval is (5.8 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+4.4 s in the 10-1000 keV band is 2.8 +/- 0.2 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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