TITLE:   GCN CIRCULAR
NUMBER:  18755
SUBJECT: GRB 151228B: Fermi GBM observation
DATE:    15/12/29 16:58:45 GMT
FROM:    Peter Veres at UAH  <veresp@gmail.com>

P Veres (UAH) reports on behalf of the Fermi GBM Team:

"At 22:47:12.59 UT on 28 December 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 151228B (trigger 473035636 / 151228949).
which was also detected by the Swift/BAT (Lien et al. 2015, GCN 18739).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 107 degrees.

The GBM light curve shows of a single pulse
with a duration (T90) of about 29 s (50-300 keV). There was a
Solar flare coincident with this GRB which affected the low
energy channels of GBM. For this reason the spectral analysis
was carried out for photon energies above 40 keV.
The time-averaged spectrum from T0-6.1 s to T0+21.5 s is
adequately fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.1 +/- 0.4 and
the cutoff energy, parameterized as Epeak, is 93 +/- 9 keV.

The event fluence (10-1000 keV) in this time interval is
(3.6 +/- 0.4)E-6 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+2.3 s in the 10-1000 keV band
is 7.6 +/- 0.9 ph/s/cm^2.

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

[GCN OPS NOTE(29dec15): Per author's request, the "29A" in the Subject-line
was changed to "28B", and the "2008"  was changed to "2015" in the citation.]