TITLE:   GCN CIRCULAR
NUMBER:  9295
SUBJECT: GRB 090428B: Fermi GBM detection
DATE:    09/04/29 15:22:36 GMT
FROM:    Elisabetta Bissaldi at MPE  <ebs@mpe.mpg.de>

Elisabetta Bissaldi (MPE) reports on behalf of the Fermi GBM Team:


"At 13:15:11.06 UT on 28 April 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090428B (trigger 262617313 / 090428552).
The on-ground calculated location, using the GBM trigger
data, is RA = 0.8, DEC = +6.5 (J2000 degrees,
equivalent to 00h 03m, 06d 30'), with an uncertainty
of 4.4 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 101 degrees.

The GBM light curve consists of a broad single peak
with a duration (T90) of about 30 s (8-1000 keV).
The time-averaged spectrum from T0-9.2 s to T0+15.3 s is
adequately fit by a power law function with an exponential
high energy cutoff. The power law index is -1.86 +/- 0.07
and the cutoff energy, parameterized as Epeak,
is 65 +/- 16 keV (chi squared 279 for 241 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(5.2 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.1 s in the 8-1000 keV band
is 10.1 +/- 0.7 ph/s/cm^2.

A Band function fits the spectrum equally well
(chi squared 278 for 240 d.o.f.) with Epeak = 53 +/- 19 keV,
alpha = -1.81 +/- 0.13 and beta = -2.17 +/- 0.21.


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