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GCN Circular 9566

Subject
GRB 090623: Fermi GBM detection
Date
2009-06-23T14:52:32Z (15 years ago)
From
Arne Rau at MPE <arau@mpe.mpg.de>
Arne Rau (MPE) reports on behalf of the Fermi GBM Team:

"At 02:34:17.56 UT on 23 June 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090623 (trigger 267417259 / 090623107).

The on-ground calculated location, using the GBM trigger
data, is RA = 309.0deg, DEC = -43.2 deg (J2000 degrees,
equivalent to 20 h 36 m, -43 d 12 '), with an uncertainty
of 2.0 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 73 degrees.

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

The GBM light curve consists of at least five peaks
with a duration (T90) of about 72.2 s (8-1000 keV).
The time-averaged spectrum from T0-1.920 s to T0+40.064 s is
best fit by a power law function with an exponential
high energy cutoff.  The power law index is -0.73 +/- 0.04 and
the cutoff energy, parameterized as Epeak, is 476 +/- 39 keV
(chi squared 738 for 655 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(9.60 +/- 0.02)E-06 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+0.003 s in the 8-1000 keV band
is 3.30 +/- 0.04 ph/s/cm^2.

A Band function fits the spectrum equally well (chi squared 737 for 654 
d.o.f.)
with Epeak= 428 +/- 51 keV, alpha = -0.69 +/- 0.05 and beta = -2.3 +/- 0.4.

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