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GCN Circular 9415

GRB 090516: Fermi GBM observation
2009-05-21T08:51:16Z (15 years ago)
Sheila McBreen at MPE <>
Sheila McBreen (UCD/MPE)
reports on behalf of the Fermi GBM Team:

"At 08:27:58.35 UT on 16 May 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090516 (trigger 264155280 / 090516353).
which was also detected by the Swift-BAT
(Rowlinson et al. 2009, GCN 9374).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 20 degrees.

The GBM light curve consists of about five overlapping
pulses from T0-50 s to T+120 s. There is continued weak emission
until about T0+300 s (8-1000 keV).

Due to a large change in the spacecraft pointing during this long
burst, a time averaged spectrum could not be fit. Instead three
spectral intervals from -50 to 20 sec, 20 to 60 sec
and 60 to 120 seconds were selected.

The first interval was well fit by a power law function with
an exponential high energy cutoff.  The power law index
is -1.51 ( +/-0.11 ) and the cutoff energy, parameterized as
Epeak, is 185.6 (+98.4/-42.5) keV.

The second and third intervals are adequately fit by a Band function.
The parameters for interval two are alpha = -1.03 (+0.26/-0.31) ,
Epeak = 51.4 (+20.1, -11.4), beta= -2.1 ( +0.1/-0.2)
and for the third interval, alpha = 0.30 (+1.30/ - 0.78),
Epeak = 27.87 +/- 5.0), beta = -2.64 +/-0.4.

The sum of the event fluence (8-1000 keV) in these time intervals is
(2.3 +/- 0.5)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+28.6 s in the 8-1000 keV band
is 5.3 +/- 0.2 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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