[vsnet-grb-info 18835] GRB 161218B: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20286
SUBJECT: GRB 161218B: Fermi GBM detection
DATE:    16/12/18 18:19:00 GMT
FROM:    Rachel Hamburg at UAH  <rkh0007 at uah.edu>

R. Hamburg (UAH), C. Meegan (UAH), and H. Yu (MPE)
report on behalf of the Fermi GBM Team:

"At 08:32:40.65 UT on 18 December 2016, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 161218B (trigger 503742764 / 161218356).

The on-ground calculated location, using the GBM trigger
data, is RA = 358.64, DEC = -16.95, with an uncertainty
of 1.00 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which we have characterized as a core-plus-tail model, with 90% of
GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg
systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ).

The trigger resulted in an Autonomous Repoint Request (ARR)
by the GBM Flight Software owing to the high peak flux of the GRB.
This ARR was accepted and the spacecraft slewed to the GBM in-flight
location. The initial angle from the Fermi LAT boresight to
the GBM ground location is 80 degrees.

The GBM light curve consists of multiple peaks
with a duration (T90) of about 26 s (50-300 keV).
The time-averaged spectrum from T0-2.0 s to T0+32.8 s is
best fit by a Band function with Epeak = 214.80 +/- 2.51 keV,
alpha = -0.51 +/- 0.01, and beta = -3.06 +/- 0.10.

The event fluence (10-1000 keV) in this time interval is
(8.91 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.7 s in the 10-1000 keV band
is 74.1 +/- 0.6 ph/s/cm^2.

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