[vsnet-grb-info 17359] GRB 151227A: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18726
SUBJECT: GRB 151227A: Fermi GBM detection
DATE:    15/12/27 10:53:33 GMT
FROM:    Elisabetta Bissaldi at U.Innsbruk/IAPP  <Elisabetta.Bissaldi at uibk.ac.at>

P Veres (UAH) and Kilian Toelge (MPE)
report on behalf of the Fermi GBM Team:


"At 01:44:07.69 UT on 27 December 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 151227A (trigger 472873451 / 151227072).


The on-ground calculated location, using the GBM trigger
data, is RA = 205.5, DEC = +65.9 (J2000 degrees,
equivalent to 13h 42m, 65d 52'), with an uncertainty
of 1.5 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]).

This burst was also independently detected by INTEGRAL SPI-ACS.

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 best location is 32 degrees.

The GBM light curve consists of a single pulse
with a duration (T90) of about 3.4 s (50-300 keV).
The time-averaged spectrum from T0 to T0 + 8.9 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.91 +/- 0.05 and
the cutoff energy, parameterized as Epeak, is 155 +/- 7 keV.

The event fluence (10-1000 keV) in this time interval is
(5.0 +/- 0.1)E-6 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.8 s in the 10-1000 keV band
is 20.5 +/- 0.4 ph/s/cm^2.


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