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GCN Circular 32637

Subject
GRB 221009A or Swift J1913.1+1946: Fermi-LAT detection
Date
2022-10-09T21:45:05Z (a year ago)
From
Elisabetta Bissaldi at INFN,Bari <elisabetta.bissaldi@ba.infn.it>
E Bissaldi (Politecnico and INFN Bari), N. Omodei (Stanford Univ.),
M. Kerr (NRL), report on behalf of the Fermi-LAT team:


At 14:17:05.99 on October, 09, 2022 Fermi-LAT detected high-energy emission
from Swift J1913.1+1946 or GRB 221009A, which was reported by
Swift (Dichiara et al. GCN #32632) and by GBM (Veres et al. GCN #32636).
The best LAT on-ground location is found to be

RA, Dec = 288.21, 19.73 (J2000)

with an error radius of 0.09 deg (90 % containment, statistical error only).
This was 94 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 500-3500 s after
the Swift trigger is (1.27 +/- 0.16)E-05 ph/cm2/s.
The estimated photon index above 100 MeV is -2.12 +/- 0.11.
The highest-energy photon is a 7.8 GeV
which is observed 766 seconds after the Swift trigger.

The Fermi-LAT point of contact for this burst is
Elisabetta Bissaldi (elisabetta.bissaldi@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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