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/"
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