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GCN Circular 15591

GRB 131209A: Fermi GBM observation
2013-12-11T12:21:13Z (10 years ago)
Andreas von Kienlin at MPE <>
A. von Kienlin (MPE) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 13:07:56.97 UT on 09 December 2013, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 131209A (trigger 408287279 / 131209547),
which was also detected by the Fermi/LAT(Vianello et al. 2013, GCN 15587),
Konus-Wind (Golenetskii et al. 2013, GCN 15589) and INTEGRAL SPI-ACS. 
The GBM on-ground location is consistent with the error box derived by
the intersection of the IPN annulus with the Fermi-LAT 1 sigma 
error circle (Hurley et al. 2013, GCN 15588).

The GBM light curve shows a structured pulse
with a duration (T90) of about 14 s (50-300 keV).
The time-averaged spectrum from T0-2.560 s to T0+19.968 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.46 (+0.04/-0.04)  and
the cutoff energy, parameterized as Epeak, is 287 (+12/-11)keV

The event fluence (10-1000 keV) in this time interval is
(1.44 +/- 0.03)E-05 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+11.328 s in the 10-1000 keV band
is 8.0 +/- 0.3  ph/s/cm^2.

A Band function fits the spectrum equally well with Epeak= 267 (+17/-14)
alpha = -0.41 (+0.06/-0.05)  and beta = -2.79 (+0.24/-0.61).

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