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GCN Circular 8912

GRB 090222: Fermi GBM detection
2009-02-22T16:23:16Z (15 years ago)
Andreas von Kienlin at MPE <>
A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: 

"At 04:17:09.58  UT on 22 February 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090222 (trigger 256969031 / 090222179).

The on-ground calculated location, using the GBM trigger 
data, is RA = 120.2, DEC = +43.4 (J2000 degrees, 
equivalent to 08h 01m, +43d 24'), with an uncertainty 
of 5.5 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 80 degrees.

The GBM light curve shows one main peak with substructure 
with a duration (T90) of about 18 s (8-1000 keV). 
The time-averaged spectrum from T0-2.688 s to T0+14.720 s is 
well fit by a power law function with an exponential
high energy cutoff.  The power law index is -1.00 +/- 0.11 
and the cutoff energy, parameterized as Epeak, is 157.7 +/- 19.8 keV
(chi squared 523.89 for 480 d.o.f.).

The event fluence (8-1000 keV) in this time interval is 
(2.19 +/- 0.19)E-06 erg/cm^2. The 1-sec peak photon flux measured 
starting from T0+6.528 s in the 8-1000 keV band 
is 1.10 +/- 0.14 ph/s/cm^2.

A Band function fits the spectrum equally well 
(chi squared 522.58 for 479 d.o.f.) with 
Epeak= 147.9 +/- 27.1  keV, alpha = -0.97 +/- 0.14 
and beta = -2.56 +/- 0.66. 

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