[vsnet-grb-info 7346] GRB 090222: Fermi GBM detection
GCN Circulars
gcncirc at capella.gsfc.nasa.gov
Mon Feb 23 01:23:24 JST 2009
TITLE: GCN CIRCULAR
NUMBER: 8912
SUBJECT: GRB 090222: Fermi GBM detection
DATE: 09/02/22 16:23:16 GMT
FROM: Andreas von Kienlin at MPE <azk at mpe.mpg.de>
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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