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GCN Circular 9792

GRB 090813: Fermi GBM observation
2009-08-13T16:48:15Z (15 years ago)
Andreas von Kienlin at MPE <>
A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: 

"At 04:10:42.59 UT on 13 August 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090813 (trigger 271829444  / 090813174), which 
was also detected by the SWIFT-BAT (Cummings et al. 2009, GCN 9781)
and Konus/Wind (Golenetskii et al., 2009, GCN Circular 9787).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 35.3 degrees.

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

The GBM light curve consists of two separate pulses with a 
duration (T90) of about 9 s (8-1000 keV). The time-averaged 
spectrum from T0-0.256 s to T0+8.960 s is well fit by a 
power law function with an exponential high energy cutoff. 
The power law index is -1.43 +/- 0.08 an the cutoff energy, 
parameterized as Epeak, is 161 +/- 26 keV
(chi squared 495 for 480 d.o.f.).

The event fluence (8-1000 keV) in this time interval is 
(3.5 +/- 0.2)E-06 erg/cm^2. The 1.024-sec peak photon flux measured 
starting from T0+0.512 s in the 8-1000 keV band 
is 14.4 +/- 0.5 ph/s/cm^2.

A Band function fits the spectrum equally well (chi squared 492 
for 479 d.o.f.) with Epeak= 95 +/- 30 keV, alpha = -1.25 +/- 0.18 
and beta = -2.0 +/- 0.1. 

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