GCN Circular 8821

Valerie Connaughton (UAH) reports on behalf of the Fermi GBM Team:

"At 15:22:01.05 UT on 17 Jan 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090117 (trigger 253898523 / 090117640)
which was also detected by SuperAGILE (Donnarumma et al. 2009,
GCN 8817
Not found
 
 
).

The GBM on-ground location is consistent with the reported
position from SuperAGILE. The angle from the Fermi LAT boresight is
51 degrees.

The GBM light curve shows a soft event with a single peak lasting
about 2 seconds superimposed on a lower-level continuum.
The burst duration (T90) is about 21 s (8-1000 keV).
The time-averaged spectrum from T0-5 s to T0+4 s is
best fit by a Band function with Epeak = 25 +/- 2 keV,
alpha = -0.4 +/- 0.5, and beta = -2.5 +/- 0.1

The event fluence (8-1000 keV) in this time interval is
(1.8 +/- 1.3)E-6 erg/cm^2, with a 1 sec peak flux starting
at T0 of 9.6 +/- 4.2 ph/cm^2/s and a 0.256 sec peak flux starting
at T0+0.256 sec of 18.6 +/- 8.0 ph/cm^2/s.

In view of the soft spectrum and the position of the burster close to
the Galactic plane, other spectral forms were investigated that are
more typical of galactic transient sources.   Of these, the best fit was
obtained using a thermal Bremmstrahlung model with kT = 49. 
The Band GRB function was preferred statistically with delta chi2
= -5 for 1 extra parameter. It is likely, therefore, that this is a soft
GRB rather than a new galactic transient.

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