[vsnet-grb-info 20193] GRB 171227A: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22289
SUBJECT: GRB 171227A: Fermi GBM detection
DATE:    17/12/27 18:55:27 GMT
FROM:    C. Michelle Hui at MSFC/Fermi-GBM  <c.m.hui at nasa.gov>

C. M. Hui (NASA/MSFC)
reports on behalf of the Fermi GBM Team:

At 00:00:13.40 UT on 27 December 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 171227A (trigger 536025618/171227000),
also detected by AGILE/MCAL (Verrecchia et al. GCN 22288).

The on-ground calculated location, using the GBM trigger data,
is RA = 280.7 , DEC = -35.0  (J2000 degrees,
equivalent to 18h 42m, -35d 0.0'), with an uncertainty of 1.0 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 with a systematic error of more than 10 deg 
[Connaughton et al. 2015, ApJS, 216, 32] ).
The angle from the Fermi LAT boresight is 120 degrees.

The GBM light curve shows several peaks with decreasing amplitudes
and a duration (T90) of about 38 s (50-300 keV). 
The time-averaged spectrum from T0+0.0 s to T0+58.2 s is 
adequately fit by a Band function with Epeak = 771 +/- 14 keV, 
alpha = -0.87 +/- 0.01, and beta = -2.47 +/- 0.04.

The event fluence (10-1000 keV) in this time interval is 
(305.3 +/- 1.3) E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+19.4 s in the 10-1000 keV band is 90.3 +/- 0.7 ph/s/cm^2.

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