GCN Circular 22813

B. Mailyan (UAH) reports on behalf of the Fermi GBM Team:

"At 15:50:36.05 UT on 20 June 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180620B (trigger 551202641 / 180620660),
which was also detected by the Swift/BAT and XRT (Evans et al. 2018, GCN
22807
Not found
 
 
).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 137
degrees.

The GBM light curve shows multi-peaked structure
with a duration (T90) of about 46.7 s (50-300 keV).
Evans et al. 2018 report a shorter duration of
~30 s in the Swift/BAT. We suggest the discrepancy
may be due to extended hard emission of this GRB.

The time-averaged spectrum from T0 to T0+46 s
is adequately fit a power law function with an exponential
high-energy cutoff. The power law index is 0.85 +/- 0.1 and
the cutoff energy, parameterized as Epeak, is 149 +/- 11 KeV.
A Band function fits the spectrum equally well
with Epeak= 106 +/- 15 keV, alpha = -0.5 +/- 0.2 and
beta = -2.2 +/- 0.1.

The event fluence (10-1000 keV) in this time interval is
(7.7 +/- 0.04)E-06 erg/cm^2. The 1-s peak photon flux measured
starting from T0 in the 10-1000 keV band is 6.8 +/- 0.5 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."