[vsnet-grb-info 7717] GRB 090425: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9271
SUBJECT: GRB 090425: Fermi GBM detection
DATE:    09/04/27 16:10:11 GMT
FROM:    Andreas von Kienlin at MPE  <azk at mpe.mpg.de>

A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: 

"At 09:03:30.57 UT on 25 April 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090425 (trigger 262343012 / 090425377).
The on-ground calculated location, using the GBM trigger 
data, is RA = 116.1, DEC = 69.9 (J2000 degrees, 
equivalent to 07h 44m, 69d 54'), with an uncertainty 
of 2.9 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 105 degrees.

This burst was also independently detected by INTEGRAL SPI-ACS.

The GBM light curve consists of three widely separated pulses
and has a duration (T90) of about 72 s (8-1000 keV). 
The first two pulses at T0-0.6 s and T0+44 s are weak and
well fit by a simple power law functions with index -1.5 +/- 0.1 
and index -1.7 +/- 0.1 respectively. The third pulse observed at
T0+57 s is strong and structured.
The time-averaged spectrum from T0+57.537 s to T0+80.065 s is 
well fit by  a power law function with an exponential high energy cutoff.  
The power law index is -1.56 +/- 0.04  and the cutoff energy, 
parameterized as Epeak, is 142 +/- 13 keV
(chi squared 570 for 484 d.o.f.).
A Band function fits the spectrum equally well 
(chi squared 566 for 483 d.o.f.) with Epeak= 69 +/- 11 keV, 
alpha = -1.29 +/- 0.11 and beta = -2.03 +/- 0.05. 

The event fluence (8-1000 keV) in this time interval is 
(1.3 +/- 0.2)E-05 erg/cm^2. The 1-sec peak photon flux measured 
starting from T0+57.537 s in the 8-1000 keV band 
is 14.0 +/- 0.3 ph/s/cm^2.

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