TITLE:   GCN CIRCULAR
NUMBER:  23569
SUBJECT: GRB 181227A: Fermi GBM detection
DATE:    18/12/27 22:06:13 GMT
FROM:    Peter Veres at UAH  <veresp@gmail.com>

E. Bissaldi (Politecnico & INFN Bari) and P. Veres (UAH)
report on behalf of the Fermi GBM Team:

"At 06:17:00.50 UT on 27 December 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 181227A (trigger 567584225 / 181227262).

The on-ground calculated location, using the GBM trigger
data, is

RA, Dec = 24.2, -56.1

(J2000 degrees), 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 110
degrees.

The GBM light curve consists of two peaks
with a duration (T90) of about 13 s (50-300 keV).
The time-averaged spectrum from T0-0.3 s to T0+19.8 s is
best fit by a Band function with Epeak = 85 +/- 1 keV,
alpha = -0.33 +/- 0.02, and beta = -3.08 +/- 0.05.

The event fluence (10-1000 keV) in this time interval is
(6.85 +/- 0.05)E-5 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+8.9 s in the 10-1000 keV band
is 110.5 +/- 1.2 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(27dec18):  Per author's request, the alpha value
in the third paragraph was changed from "0.33" to "-0.33".]