[AAVSO-HEN] GRB 090308B: Fermi GBM detection

[grb at aavso.org]

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TITLE:   GCN CIRCULAR
NUMBER:  8963
SUBJECT: GRB 090308B: Fermi GBM detection
DATE:    09/03/09 21:42:26 GMT
FROM:    Adam Goldstein at Fermi-GBM/UAH  <adam.m.goldstein at msfc.nasa.gov>

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

"At 17:36:24.70 UT on 08 March 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090308B (trigger 258226586 / 090308734).
This burst was also independently detected by INTEGRAL SPI-ACS.

The on-ground calculated location, using the GBM trigger 
data, is RA = 22.4, DEC = -58.1 (J2000 degrees, 
equivalent to 01h 30m, 58d 05'), with an uncertainty 
of 2.3 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 50 degrees.

The GBM light curve consists of two peaks with substructure
with a duration (T90) of about 2.11 s (8-1000 keV). 
The time-averaged spectrum from T0-0.25 s to T0+1.53 s is 
well fit by a power law function with an exponential
high energy cutoff.  The power law index is -0.54 +/- 0.11 and
the cutoff energy, parameterized as Epeak, is 710.3 +/- 100.0 keV
(chi squared 342 for 362 d.o.f.).

The event fluence (8-1000 keV) in this time interval is 
(3.46 +/- 0.13)E-06 erg/cm^2. The 0.128-sec peak photon flux measured 
starting from T0+0.64 s in the 8-1000 keV band 
is 14.22 +/- 0.91 ph/s/cm^2.

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