GCN Circular 30947
Subject
GRB 211018A: Fermi GBM observation
Date
2021-10-19T17:18:39Z (3 years ago)
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 GBM Team:
"At 22:28:13.94 UT on 18 October 2021, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 211018A (trigger 656288898 / 211018936),
which was also detected by the Fermi LAT (M. Axelsson et al. 2021, GCN 30943),
and GRBAlpha (M. Ohno, GCN 30945). The GBM on-ground location is consistent
with the Fermi-LAT position.
The angle from the Fermi LAT boresight at the GBM trigger time is 68 degrees.
The GBM light curve consists of multiple peaks
with a duration (T90) of 123.9 s (50-300 keV).
The time-averaged spectrum from T-2.4s to T0+142.0 s is
well fit by a power law function with an exponential
high-energy cutoff. The power law index is -0.75 +/- 0.01 and
the cutoff energy, parameterized as Epeak, is 351.4 +/- 4.9 keV.
The Band function also fits the burst equally well, with parameters,
alpha= -0.74 +/- 0.01, beta= -3.13 +/- 0.28 and Epeak of 344.6 +/- 6.2 keV.
The event fluence (10-1000 keV) in the T90 interval is
(1.53347 +/- 0.0003)E-04 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+134.5 s in the 10-1000 keV band
is 15.6 +/- 0.3 ph/s/cm^2.
We note that owing to the large total fluence of this burst,
the 1-sec peak photon flux begins after the T90.
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/"