[vsnet-grb-info 7746] GRB 090426C: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9300
SUBJECT: GRB 090426C: Fermi GBM detection
DATE:    09/04/29 20:21:03 GMT
FROM:    Alexander van der Horst at NASA/MSFC  <Alexander.J.VanDerHorst at nasa.gov>

A.J. van der Horst (NASA/MSFC/ORAU) reports on behalf of the
Fermi GBM Team:

"At 16:33:49.27 UT on 26 April 2009, the Fermi Gamma-ray Burst Monitor
(GBM) triggered and located GRB 090426C (trigger 262456415 / 090426.690).
The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 82.7, Dec = -9.7 (J2000 degrees, equivalent to
J2000 5h31m, -9d40'), with a statistical uncertainty of 2.0 degrees
(radius, 1-sigma containment, statistical only; there is additionally
a systematic error which is currently estimated to be 2 to 3 degrees).
The angle from the Fermi LAT boresight is 69 degrees.

The GBM light curve consists of one main pulse, with a duration of ~12
seconds. The time-averaged spectrum from T0-0.4 to T0+9.9 s is adequately
fit by a power law with an exponential high-energy cutoff, but can also
be well fit by a Band function, although the beta value for the latter
is poorly constrained. For the power law with exponential cutoff, the
index is -1.31 +/- 0.09 and the cutoff energy, parameterized as Epeak,
is 351 +150/-81 keV. For the Band function, alpha is -1.29 +/- 0.11,
beta is -1.98 +0.17/-0.64 and Epeak is 295 +166/-83.
The fluence (8-1000 keV) in this time interval is (3.1 +/- 0.2)E-6 
erg/cm^2.
The 1-sec peak photon flux measured starting from T0+0.7s in the
8-1000 keV band is 6.8 +/- 0.7 ph/s/cm^2.

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