[vsnet-grb-info 14330] GRB 131231A: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15644
SUBJECT: GRB 131231A: Fermi GBM detection
DATE:    14/01/01 00:42:48 GMT
FROM:    Peter Jenke at MSFC  <peter.a.jenke at nasa.gov>

P. Jenke (UAH) and S. Xiong (UAH) reports on behalf of the Fermi GBM Team:

"At 04:45:16.083 UT on December 31 2013, the Fermi Gamma-Ray
Burst Monitor triggered and located 
GRB 131231A (trigger 410157919/131231198). 
This GRB was detected in a ground analysis by 
the Fermi LAT (Sonbas et al. GCN 15640).  
It was also detected in optical follow-up observations
of the GBM position by DARK/NBI (Xu et al. GCN 15641) 
and iPTF (Singer et al. GCN 15643), and confirmed by NOT 
observations of the Fermi LAT position (Malesani et al. GCN 15642). 
The on-ground calculated location from GBM is consistent 
with the positions reported from these follow-up observations.

The trigger resulted in an Autonomous Repoint Request (ARR) 
that was accepted and the LAT slewed to the GBM in-flight 
location. The initial angle from the LAT boresight is 38 deg
from Fermi/GBM position.  

The GBM light curve consists of a single large peak preceded 
by a smaller peak which resulted in the trigger.  The 
duration (T90) of the burst was about 31 s (50-300 keV).
The time-averaged spectrum from T0+.003 s to T0+56 s is 
best fit with a Band function  with Epeak = 146 +/- 3 keV, 
alpha = -1.10 +/- 0.01 and beta = -2.14 +/- 0.01.

The event fluence (10-1000 keV) in this time interval is
 (2.51 +/- 0.01)E-06 erg/cm^2. The 1.0-sec peak photon flux 
measured starting from T0+22 s in the 10-1000 keV band
is 67.3 +/- 0.8 ph/s/cm^2.

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