TITLE:   GCN CIRCULAR
NUMBER:  31409
SUBJECT: GRB 220107B: Fermi-LAT detection
DATE:    22/01/08 06:05:07 GMT
FROM:    Magnus Axelsson at Stockholm U.  <magaxe@kth.se>

M. Arimoto (Kanazawa Univ.), N. Di Lalla (Stanford Univ.), M. Axelsson (KTH & Stockholm Univ.) and S. Cutini (INFN Perugia) report on behalf of the Fermi-LAT Collaboration:

On January 7th, 2022, Fermi-LAT detected high-energy emission from GRB 220107B, which was also detected by Fermi-GBM  (trigger 663274898/220107793).

The best LAT on-ground location is found to be

RA, Dec = 216.5, 20.0 (degrees, J2000)

with an error radius of 0.22 deg (90% containment, statistical error only).
This was 54 deg from the LAT boresight at the time of the GBM trigger:

T0 =  19:01:33.52 UT.

The data from the Fermi-LAT show a significant increase in the event rate after the GBM trigger that is temproally and spatially correlated with the GBM emission (2.3 degrees from the GBM location) with high significance. The photon flux above 100 MeV in the time interval 0-500s after the GBM trigger is 1.4E-5 +/- 2.4E-6 ph/cm2/s.

The estimated photon index above 100 MeV is -2.14 +/- 0.17.

The highest-energy photon is a 2.4 GeV event which is observed ~8 seconds after the GBM trigger.

A Swift ToO has been approved for this burst.

The Fermi-LAT point of contact for this burst is Sara Cutini (sara.cutini@pg.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.