TITLE: GCN CIRCULAR NUMBER: 37341 SUBJECT: GRB 240828A: Fermi GBM Observation DATE: 24/08/29 19:24:23 GMT FROM: Sarah Dalessi at UAH sd0104@uah.edu

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

"At 14:55:06.83 UT on 28 August 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 240828A (trigger 746549711/240828622). which was also detected by AstroSat (S. Srijan et al. 2024, GCN 37328), Fermi-LAT (R. Gupta et al. 2024, GCN 37331), Swift-XRT (A.P. Beardmore et al. 2024, GCN 37337), and KAIT (W. Zheng et al. 2024 37339) The Fermi GBM on-ground location is consistent with the AstroSat, Fermi-LAT, Swift-XRT, and KAIT positions.

The angle from the Fermi LAT boresight is 97 degrees.

The GBM light curve multiple peaks with a duration (T90) of about 41.2 s (50-300 keV). The time-averaged spectrum from T0+0.002 to T0+44.225 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.96 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 850 +/- 30 keV.

The event fluence (10-1000 keV) in this time interval is (8.05 +/- 0.07)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+38.8 s in the 10-1000 keV band is 18.6 +/- 0.4 ph/s/cm^2.

A Band function fits the spectrum equally well with Epeak= 820 +/- 30 keV, alpha = -0.96 +/- 0.01 and beta = -2.9 +/- 0.2.

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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