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GCN Circular 32568

Subject
GRB 220921A: Fermi-LAT detection
Date
2022-09-21T19:17:34Z (a year ago)
From
Roberta Pillera at Politecnico and INFN Bari <roberta.pillera@ba.infn.it>
R. Pillera (Politecnico and INFN Bari), E. Bissaldi (Politecnico and 
INFN Bari),
N. Di Lalla (Stanford Univ.) report on behalf of the Fermi-LAT team:

At 11:05:59.07 UTC on September, 21, 2022 Fermi-LAT detected high-energy 
emission from GRB 220921A,
which was also detected by Fermi GBM (trigger 685451164 / 220921462).

The best LAT on-ground location is found to be

RA, Dec = 66.79, -40.25 (J2000)

with an error radius of 0.42 deg (90 % containment, statistical error 
only).
This was 69 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 0-2000 s after the 
GBM trigger
is (3.1 +/- 0.1)E-06 ph/cm2/s.
The estimated photon index above 100 MeV is -2.1 +/- 0.3.
The highest-energy photon is a 866 MeV event which is observed 935 
seconds after the GBM trigger.

A Swift ToO has been requested for this burst.

The Fermi-LAT point of contact for this burst is
Roberta Pillera (roberta.pillera@ba.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.
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