TITLE:   GCN CIRCULAR
NUMBER:  22136
SUBJECT: GRB 171120A: Fermi-LAT detection
DATE:    17/11/20 20:39:29 GMT
FROM:    Giacomo Vianello at SLAC  <giacomov@slac.stanford.edu>

F. Longo (University and INFN, Trieste), G. Vianello (Stanford),
D. Kocevski (NASA/GSFC) and M.Arimoto (Waseda University)

report on behalf of the Fermi-LAT collaboration:

At 13:20:02 on November 20, 2017, Fermi-LAT detected high-energy emission
from GRB 171120A,which was also detected by Swift-BAT (Tohuvavohu et al.,
GCN 22133) and by Fermi-GBM (trigger 532876807/171120556).

The best LAT on-ground location is found to be

RA, Dec = 163.84, 22.40 deg (J2000)

with an error radius of 0.17 deg (90% containment, statistical error only).

This was 24 deg from the LAT boresight at the time of the trigger.

The LAT on-ground position is consistent with the Swift-XRT localization (Evans
et al., GCN 22135).

More than 30 photons above 100 MeV are observed within ~ 6.5 ks seconds of
the trigger.  The highest-energy photon is a 3.4 GeV event which is observed
~4.8 ks seconds after the GBM trigger.

The Fermi-LAT point of contact for this burst is:

Francesco Longo (francesco.longo@ts.infn.it).

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.