TITLE:   GCN CIRCULAR
NUMBER:  32212
SUBJECT: GRB 220617A: Fermi-LAT detection
DATE:    22/06/18 01:57:08 GMT
FROM:    Niccolo Di Lalla at Stanford U  <niccolo.dilalla@stanford.edu>

N. Di Lalla (Stanford Univ.), M. Arimoto (Kanazawa Univ.), M. Axelsson 
(KTH & Stockholm Univ.) and
G. Principe (University and INFN Trieste) report on behalf of the 
Fermi-LAT team:

On June 17, 2022, Fermi-LAT detected high-energy emission from GRB 220617A,
which was also detected by Fermi-GBM (trigger 677183477 / 220617772, GCN 
32209).

The best LAT on-ground location is found to be

RA, Dec = 156.96, 15.53 (degrees, J2000)

with an error radius of 0.09 deg (90 % containment, statistical error 
only).
This was 46 deg from the LAT boresight at the time of the GBM trigger:

T0 = 18:31:12 UT.

The data from the Fermi-LAT show a significant increase in the event rate
that is spatially and temporally correlated with the GBM emission with 
high significance.
The photon flux above 100 MeV in the time interval 0-200 s
after the GBM trigger is (4.9 +/- 0.8)E-05 ph/cm2/s.

The estimated photon index above 100 MeV is -1.9 +/- 0.1.

The highest-energy photon is a 8.2 GeV event which is observed 0.9 
seconds after the GBM trigger.

A Swift ToO has been approved for this burst.

The Fermi-LAT point of contact for this burst is Giacomo Principe 
(giacomo.principe@ts.infn.it <mailto:giacomo.principe@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.