GCN Circular 22990
Subject
GRB 180720C: Fermi GBM observation
Date
2018-07-21T05:39:40Z (6 years ago)
From
Oliver J Roberts at USRA/NASA <oliver.roberts@nasa.gov>
O.J. Roberts (USRA/NASA) and C. Meegan (UAH) report on behalf
of the Fermi GBM Team:
"At 22:23:53.15 UT on 20 July 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180720C (trigger 553818238 / 180720933),
which was also detected by Swift (S.J. LaPorte et al. 2018, GCN 22982).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight at the GBM trigger time using
the Swift-XRT position is 111 degrees.
The GBM light curve consists of broad, single peak with a
duration (T90) of about 23 s (50-300 keV). The time-averaged spectrum
from T0-6.1 to T0+17.4 s is adequately fit by a power law function
with an exponential high-energy cutoff. The power law index is
-1.12 +/- 0.08 and the cutoff energy, parameterized as Epeak,
is 583 +/- 161 keV.
The event fluence (10-1000 keV) over this time interval is
(2.83 +/- 0.05)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+4.3 s in the 10-1000 keV band is 2.8 +/- 0.3 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."