[vsnet-grb-info 20892] GRB 180720C: Fermi GBM observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22990
SUBJECT: GRB 180720C: Fermi GBM observation
DATE:    18/07/21 05:39:40 GMT
FROM:    Oliver J Roberts at USRA/NASA  <oliver.roberts at 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."