[vsnet-grb-info 7958] GRB 090531B: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9501
SUBJECT: GRB 090531B: Fermi GBM detection
DATE:    09/06/10 01:07:56 GMT
FROM:    Sylvain Guiriec at UAH  <sylvain.guiriec at lpta.in2p3.fr>

S. Guiriec (UAH)
reports on behalf of the Fermi GBM Team:

"At 18:35:56.49 UT on 31 May 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090531B (trigger 265487758 / 090531775)
which was also detected by the SWIFT-BAT (Cummings et al. 2008, GCN 9461).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight is 25 degrees.

The GBM light curve consists of a single peak with a duration (T90) of
about 2 s (8-1000 keV).
The time-averaged spectrum from T0-0.23 s to T0+0.77 s is
adequately fit by a Band function with Epeak = 2166(+675-408) keV,
alpha = -0.71(+0.10-0.10), and beta = -2.47(+0.25-0.46)
(Castor C-Stat 780 for 602 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(6.20 +/- 0.18)E-07 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.23 s in the 8-1000 keV band is 1.49 +/- 0.04 ph/s/cm^2.

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