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GCN Circular 8263

Subject
GRB 080916A: Fermi GBM detection
Date
2008-09-17T22:39:42Z (16 years ago)
From
Elisabetta Bissaldi at MPE <ebs@mpe.mpg.de>
E. Bissaldi (MPE), S. McBreen (MPE),
C.A. Wilson-Hodge (NASA/MSFC) and A. von Kienlin (MPE) 
report on behalf of the Fermi GBM Team: 


"At 09:45:18 UT on 16 September 2008, the Fermi Gamma-ray Burst Monitor
triggered and located GRB 080916A (trigger 243251119 / 080916406), which
was also detected by Swift (Ziaeepour et al., GCN 8237) and
Konus-Wind (Golenetskii et al., GCN 8259). The on-ground 
calculated location, using the Fermi GBM trigger data, is 
RA = 331.5, Dec = -58.1 (equivalent to J2000 
22h 06m, -58d 06'), with a statistical uncertainty of 3.2 degrees 
(radius, 1-sigma containment; there is additionally a systematic 
error which is currently estimated to be 2 to 3 degrees). 
This position is 2.8 deg from the Swift refined position
(Evans et al., GCN 8241). The angle from the Fermi LAT boresight 
to the Swift position is 76 degrees.

This long GRB consists of several peaks, with the brightest one
lasting from T0 to T0+13 s and a second peak from T0+13 s to T0+24 s
followed by weaker emission.
T90 (25-1000 keV) is about 60 sec, in agreement with 
the Swift-BAT refined analysis (Baumgartner et al., GCN 8243),
and T50 (25-1000 keV) is about 25 s.

The time-averaged spectrum from T0 to T0+58 sec is 
adequately fit by a power law function with an exponential
high energy cutoff.  The power law index is -0.9 +/-0.1 and
the cutoff energy, parameterized as Epeak, is 109 +/- 9 keV.

The fluence (25-1000 keV) is 1.5 (+/- 0.5)E-05 erg/cm2
and the peak flux (25-1000 keV) on the 1 s timescale
is 4.5 (+/- 0.7) ph/cm2/s.


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