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GCN Circular 31896

GRB 220408B: Fermi-LAT detection
2022-04-13T15:49:24Z (2 years ago)
Elisabetta Bissaldi at INFN,Bari <>
E. Bissaldi (Politecnico and INFN Bari), M. Arimoto (Kanazawa Univ.),
S. Ciprini (INFN and ASI), F. Giacchino (INFN Roma Tor Vergata and ASI),
M. Giroletti (INAF/IRA Bologna), and L. Scotton (CNRS/IN2P3/LUPM)
report on behalf of the Fermi-LAT team:

"On April 8, 2022, Fermi-LAT detected high-energy emission from GRB 220408B,
which was also detected by Fermi-GBM (trigger 671095689 / 220408311, GCN 31854),
AstroSat CZTI (Gopalakrishnan et al. 2022, GCN 31863) and was reported by the IPN
(Kozyrev et al. 2022. GCN 31878).

The best LAT on-ground location is found to be

RA, Dec = 92.48, -50.97 (degrees, J2000)

with an error radius of 0.06 deg (90 % containment, statistical error only).
This was 30 deg from the LAT boresight at the time of the GBM trigger:

T0 = 07:28:04.65 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 0-2500s
after the GBM trigger is (2.0 +/- 0.5)E-06 ph/cm2/s.

The estimated photon index above 100 MeV is -1.9 +/- 0.2.

The highest-energy photon is a 22 GeV event
which is observed 42 seconds after the GBM trigger.

The Fermi-LAT point of contact for this burst is
Elisabetta Bissaldi (

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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