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GCN Circular 32843

GRB 221025A: Fermi-LAT detection
2022-10-25T11:43:09Z (2 years ago)
Makoto Arimoto at Tokyo Inst of Tech <>
Arimoto M. (Kanazawa University) Pillera R. (Politecnico and INFN
Bari), and Maheso D. (Johannesburg Univ.) report on behalf of the
Fermi-LAT team:

At 00:58:18.42 on October, 25, 2022 Fermi-LAT detected high-energy emission
from GRB 221025A, GBM trigger 221025041 / 688352303 at 00:58:18.42 UT.

The best LAT on-ground location is found to be

RA, Dec =  133.4, 11.0 (J2000)

with an error radius of 1.3 deg (90 % containment, statistical error only).
This was 45 deg from the LAT boresight at the time of the trigger.

The data from the Fermi-LAT show a significant increase in the event
rate that is spatially
and temporally correlated with the trigger with high significance.

The 100 MeV - 1 GeV photon flux in the time interval 0-200 s after
the GBM trigger is (2.1 +/- 0.6)E-05 ph/cm2/s.
The estimated integrated photon index above 100 MeV is -2.3 +/- 0.3.
The highest-energy photon is a 1.3 GeV event with 93% probability
which is observed 3 seconds after the GBM trigger.

A Swift ToO has been requested for this burst.

The Fermi-LAT point of contact for this burst is
Dimakatso Jeannett Maheso (

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.
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