[vsnet-grb-info 8015] GRB 090621: Fermi GBM observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9556
SUBJECT: GRB 090621: Fermi GBM observation
DATE:    09/06/22 17:28:10 GMT
FROM:    Arne Rau at MPE  <arau at mpe.mpg.de>

Arne Rau (MPE) reports on behalf of the Fermi GBM Team:

"At 04:26:34.49  UT on 21 June 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090621 (trigger 267251196  / 090621185) which was
also detected by the Swift/BAT (Curan et al. 2009, GCN 9540). The GBM
triggered on the second BAT trigger (355304) and at approx. 4 min after the
initial BAT trigger (355303) for this event. The GBM on-ground location is
consistent with the Swift position.
 
The angle from the Fermi LAT boresight is 12 degrees.

The GBM light curve shows a faint peak coinciding with the initial Swift
trigger (355303) and two brighter peaks starting at the GBM trigger time.
The burst duration (T90) including the first faint peak is about 294 s
(8-1000 keV).

The time-averaged spectrum of the two brighter peaks starting from the GBM
trigger time T0-6.10 s to T0+45.06 s is best fit by a Band function with
Epeak = 56.0 +/- 10.7 keV, alpha = -1.1 +/- 0.2, and beta = -2.12 +/- 0.09
(chi squared 377 for 366 d.o.f.).

The event fluence (8-1000 keV) in the above time interval is
(4.4 +/- 1.0)E-06 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+35.840 s in the 8-1000 keV band is  1.92 +/- 0.06 
ph/s/cm^2.

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