[vsnet-grb-info 7748] GRB 090427C: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9302
SUBJECT: GRB 090427C: Fermi GBM detection
DATE:    09/04/29 20:28:46 GMT
FROM:    Michael S. Briggs at UAH and MSFC  <michael.briggs at nasa.gov>

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

"At 16:30:23.81 UT on 27 April 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090427C (trigger 262542625  / 090427688).

The on-ground calculated location, using the GBM trigger
data, is RA = 356.2, DEC = -34.6 (J2000 degrees,
equivalent to 23 h 45 m, -34 d 36'), with an uncertainty
of 5.8 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 81 degrees.

The GBM light curve shows two peaks and has a
duration (T90) of about 12.5 s (8-1000 keV).
The time-averaged spectrum from T0-2.048 s to T0+12.288 s is
well fit by a power law function with an exponential
high energy cutoff.  The power law index is 0.35 +/- 0.16 and
the cutoff energy, parameterized as Epeak, is 75 +/- 3 keV.

The event fluence (8-1000 keV) in this time interval is
(1.6 +/- 0.2)E-6 erg/cm^2.

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