TITLE: GCN CIRCULAR NUMBER: 37535 SUBJECT: GRB 240916A: Fermi GBM Observation DATE: 24/09/17 16:52:35 GMT FROM: Oliver J Roberts at USRA/NASA oliver.roberts@nasa.gov
O.J. Roberts (USRA/NASA-MSFC) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 01:22:55.77 UT on 16 September 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 240916A (trigger 748142580/240916058), which was later detected by Swift XRT (Beardmore et al. 2024, GCN 37531) after two optical afterglows were initially discovered by GOTO (Gompertz et al., 2024, GCN 37522), of which GOTO24fzn/AT 2024vlp was reported to decay in the optical by the JinShan project (Jiang et al., 2024, GCN 37526), with a redshift measured by VLT/X-shooter of z=2.610 (Pieterse et al., 2024, GCN 37532).
The Fermi GBM on-ground location is consistent with the Swift XRT position.
The angle from the Fermi LAT boresight is 79 degrees.
The GBM light curve consists of a bright FRED-like pulse with a duration (T90) of about 32 s (50-300 keV). The time-averaged spectrum from T0-5.6 to T0+55.8 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.16 +/- 0.03 and the cutoff energy, parameterized as Epeak, is 710 +/- 80 keV.
The event fluence (10-1000 keV) in this time interval is (2.78 +/- 0.07)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+10 s in the 10-1000 keV band is 5.5 +/- 0.3 ph/s/cm^2.
A Band function fits the spectrum equally well with Epeak= 580 +/- 80 keV, alpha = -1.12 +/- 0.03 and beta = -2.2 +/- 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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