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GCN Circular 9895

Subject
GRB 090904B: Fermi GBM detection
Date
2009-09-04T22:01:47Z (15 years ago)
From
Adam Goldstein at Fermi-GBM/UAH <adam.m.goldstein@msfc.nasa.gov>
A. Goldstein (UAH) reports on behalf of the Fermi GBM Team: 

"At 01:24:13.93 UT on 04 September 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090904B (trigger 273720255 / 090904058), 
which was also detected by the SWIFT-BAT (D'Elia et al. 2009, GCN 9881).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 113 degrees.

The GBM light curve consists of three bright peaks
with a duration (T90) of about 71 s (8-1000 keV). 
The time-averaged spectrum from T0-9.2 s to T0+65.5 s is 
well fit by a power law function with an exponential
high energy cutoff.  The power law index is 1.41 +/- 0.08 and
the cutoff energy, parameterized as Epeak, is 149.30 +/- 22.10 keV
(chi squared 243.6 for 238 d.o.f.).

The event fluence (8-1000 keV) in this time interval is 
(2.44 +/- 0.15)E-05 erg/cm^2. The 1-sec peak photon flux measured 
starting from T0+21.5 s in the 8-1000 keV band 
is 9.8 +/- 0.7 ph/s/cm^2.

A Band function fits the spectrum equally well 
(chi squared 239.0 for 237 d.o.f.) with Epeak= 106.30 +/- 24.60 keV, 
alpha = -1.26 +/- 0.15 and beta = -2.18 +/- 0.18. 


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