GCN Circular 18727

Kilian Toelge (MPE) and Elisabetta Bissaldi (Politecnico di Bari) 
report on behalf of the Fermi GBM Team: 


"At 05:13:48.86 UT on 27 December 2015, the Fermi Gamma-Ray Burst Monitor 
triggered and located GRB 151227B (trigger 472886032 / 151227218). 
The on-ground calculated location, using the GBM trigger data, 
is RA = 287.9, DEC = 31.9 (J2000 degrees, 
equivalent to 19h 11m, 31d 54'), with an uncertainty 
of 1 degree (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 90 degrees. 

The GBM light curve consists of three pulses 
with a duration (T90) of about 43.0 s (50-300 keV). 
The time-averaged spectrum from T0+20.0 s to T0+49.7 s 
is best fit by a Band function with Epeak = 310 +/- 21 keV, 
alpha = -1.27 +/- 0.02, and beta = -2.17 +/- 0.08. 

The event fluence (10-1000 keV) in this time interval 
is (8.94 +/- 0.09)E-6 erg/cm^2. The 1-sec peak photon flux measured 
starting from T0+29.8 s in the 8-1000 keV band 
is 36.1 +/- 0.5 ph/s/cm^2.


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