[vsnet-grb-info 20181] GRB 171222A: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22277
SUBJECT: GRB 171222A: Fermi GBM detection
DATE:    17/12/23 17:13:20 GMT
FROM:    Matthew Stanbro at UAH/Fermi  <mcs0001 at uah.edu>

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.