TITLE:   GCN CIRCULAR
NUMBER:  23597
SUBJECT: GRB 181231A: Fermi-LAT detection
DATE:    18/12/31 17:55:29 GMT
FROM:    Masanori Ohno at Hiroshima University  <ohno@astro.hiroshima-u.ac.jp>

F. Dirirsa (U. Johannesburg) and M. Ohno (Hiroshima U.)
report on behalf of the Fermi-LAT team:

On December, 31, 2018 Fermi-LAT detected high-energy emission from GRB
181231A, which was also detected by Fermi-GBM (trigger 567919668 /
181231144).

The best LAT on-ground location is found to be

RA, Dec = 254.59, 0.61 (degrees, J2000)

with an error radius of 0.24 deg (90 % containment, statistical error
only).
This was 51 deg from the LAT boresight at the time of the GBM trigger:

T0 =  03:27:43.8 UT.

The data from the Fermi-LAT show a significant increase
in the event rate after the GBM trigger that is spatially correlated with
the
GBM emission (7.8 degrees from the GBM location) with high significance.
The photon flux above 100 MeV in the time interval 0-5000 s after the
GBM trigger is 2.4 (+/-1.2)E-6 ph/cm2/s.
The estimated photon index above 100 MeV is 2.21 (+/-0.37).

A Swift ToO has been requested for this burst

The Fermi-LAT point of contact for this burst is Feraol F. Dirirsa (
fdirirsa@uj.ac.za).

The Fermi-LAT is a pair conversion telescope designed to cover the energy
band from 20 MeV to greater than 300 GeV. It is the product of an
international collaboration between NASA and DOE in the U.S. and many
scientific institutions across France, Italy, Japan and Sweden.