[vsnet-grb-info 20696] GRB 180618A: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22794
SUBJECT: GRB 180618A: Fermi GBM detection
DATE:    18/06/18 15:47:53 GMT
FROM:    Rachel Hamburg at UAH  <rkh0007 at uah.edu>

R. Hamburg (UAH) and E. Bissaldi (Politecnico & INFN Bari)
report on behalf of the Fermi GBM Team:

"At 00:43:13.11 UT on 18 June 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180618A (trigger 550975398 / 180618030),
which was also detected by the Swift/BAT (LaPorte et al. 2018, GCN 22790).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 103
degrees.

The GBM light curve shows one main peak
with a duration (T90) of about 3.7 s (50-300 keV).
LaPorte et al. 2018 report a longer duration of
~20 s in the Swift/BAT. Given the soft tail following
the initial hard spike, we suggest the discrepancy
may be due to extended emission of this short GRB.

The time-averaged spectrum from T0 to T0+1.8 s
is adequately fit a power law function with an exponential
high-energy cutoff. The power law index is 1.08 +/- 0.06 and
the cutoff energy, parameterized as Epeak, is 2.8 +/- 0.8 MeV.

The event fluence (10-1000 keV) in this time interval is
(2.12 +/- 0.12)E-06 erg/cm^2. The 64-ms peak photon flux measured
starting from T0 in the 10-1000 keV band is 14.6 +/- 1.9 ph/s/cm^2.

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