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GCN Circular 22277

GRB 171222A: Fermi GBM detection
2017-12-23T17:13:20Z (6 years ago)
Matthew Stanbro at UAH/Fermi <>
M. Stanbro (UAH), C. M. Hui (NASA/MSFC) and C. Meegan (UAH)
reports on behalf of the Fermi GBM Team:

At 16:25:10.54 UT on 22 December 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 171222A (trigger 535652715/171222684) which
was also detected by the Swift/BAT and XRT (Racusin et al. 2017, GCN 22265).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 43 degrees.

The GBM light curve shows a single peak with a duration (T90)
of about 80.4s (50-300 keV).  The time-averaged spectrum from
T0+0.0s to T0+78.8s is adequately fit by a power law function with
an exponential high-energy cutoff.  The power law index is
-1.09+/- 0.27 and the cutoff energy, parameterized as Epeak,
is 29.18 +/- 2.73 keV.

The event fluence (10-1000 keV) in this time interval is
(2.27 +/- 0.13)E-06 erg/cm^2. The 1s peak photon flux measured
starting from T0+60.1s in the 10-1000 keV band is 2.3 +/- 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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