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GCN Circular 9866

Subject
GRB 090902B: Fermi GBM detection of a bright burst
Date
2009-09-02T21:19:03Z (14 years ago)
From
Elisabetta Bissaldi at MPE <ebs@mpe.mpg.de>
Elisabetta Bissaldi (MPE) and Valerie Connaughton (UAH)
report on behalf of the Fermi GBM Team: 


"At 11:05:08.31 UT on 2 September 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090202B (trigger 273582310 / 090902462).
The on-ground calculated location, using the GBM trigger
data, is RA = 264.5, DEC = 26.5 (J2000 degrees,
equivalent to 17h 38m, 26d 30'), with an uncertainty
of 1.0 degree (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 52 degrees.
Moreover, this burst was bright enough to result in
a Fermi spacecraft repointing maneuver.

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

The GBM light curve consists of a bright pulse
with a duration of about 21 s.
The time-averaged spectrum between 50 keV and 40 MeV
from T0 to T0+22 s is well fit by a Band function
with Epeak = 775 +/- 11 keV, alpha = -0.696 +/- 0.012 
and beta = -3.85 (+0.21/-0.31).

The event fluence (50 keV - 10 MeV) in this time interval is
(3.74 +/- 0.03)E-04 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+14 s in the 50 keV - 10 MeV band
is 46.1 +/- 0.3 ph/s/cm^2.


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