TITLE:   GCN CIRCULAR
NUMBER:  18787
SUBJECT: GRB 151231A: Fermi GBM observation
DATE:    15/12/31 18:46:25 GMT
FROM:    Peter Veres at UAH  <veresp@gmail.com>

P Veres (UAH), C Meegan (UAH) and A. von Kienlin (MPE)
report on behalf of the Fermi GBM Team:

"At 10:37:47.52 UT on 31 December 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 151231A (trigger 473251071 / 151231443).

The on-ground calculated location, using the GBM trigger
data, is RA = 65.6, DEC = -61.5 (J2000 degrees,
equivalent to 04 h 23 m, -61 d 32 '), with an uncertainty
of 1 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 angle from the Fermi LAT boresight at the GBM trigger time is 157 degrees.

The GBM light curve shows two well separated peaks
with a duration (T90) of about 71 s (50-300 keV).
The time-averaged spectrum from T0-2.3 s to T0+85 s is
best fit by a Band function with Epeak = 198 +/- 7 keV,
alpha = -1.00 +/- 0.04, and beta = -2.61 +/- 0.09

The event fluence (10-1000 keV) in this time interval is
(9.7 +/- 0.1)E-5 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+5.3 s in the 10-1000 keV band
is 46.9 +/- 1.5 ph/s/cm^2.


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