[vsnet-grb-info 20501] GRB 180404B: Fermi GBM observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22597
SUBJECT: GRB 180404B: Fermi GBM observation
DATE:    18/04/04 10:04:46 GMT
FROM:    Andreas von Kienlin at MPE  <azk at mpe.mpg.de>

A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team:

"At 02:11:38.64 UT on 04 April 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180404B (trigger 544500703 / 180404091),
which was also detected by the Swift/BAT (LaPorte et al. 2018, GCN 22590).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 61.3 degrees.

The GBM light curve shows a single bright peak followed by
a secondary emission episode with a duration (T90) of about 80 s (50-300 keV).
The time-averaged spectrum from T0+0.003 s to T0+33.281 s is well fit by
a power law function with an exponential
high-energy cutoff.  The power law index is -0.40 +/- 0.04 and
the cutoff energy, parameterized as Epeak, is 209 +/- 6 keV.

The event fluence (10-1000 keV) in this time interval is
(3.3 +/- 0.4)E-06 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+12.86 s in the 10-1000 keV band
is 8.0 +/- 0.3 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 204 +/- 8 keV, alpha = -0.38 +/- 0.04 and beta = -3.3 +/- 0.6.

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