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GCN Circular 31577

GRB 220209A: Fermi-LAT detection
2022-02-11T15:10:25Z (2 years ago)
Magnus Axelsson at Stockholm U. <>
M. Pesce-Rollins (INFN Pisa), D. Horan (CNRS/IN2P3/LLR), F. Piron (CNRS/IN2P3/LUPM), M. Axelsson (KTH & Stockholm Univ.), F. Longo (University and INFN, Trieste), and N. Di Lalla (Stanford) report on behalf of the Fermi-LAT Collaboration:

On February 9th, 2022, Fermi-LAT detected high-energy emission from GRB 220209A, which was also detected by Fermi-GBM  (GCN 31561), GECAM (GCN 31564) and AGILE (GCN 31565).

The best LAT on-ground location is found to be

RA, Dec = 352.13, 73.11 (degrees, J2000)

with an error radius of 1.4 deg (90% containment, statistical error only).

This was 68 deg from the LAT boresight at the time of the GBM trigger:

T0 =  23:00:50  UT.

The data from the Fermi-LAT show a significant increase in the event rate about 10 s after the GBM trigger that is temporally correlated with the GBM emission with high significance. The GRB has a very soft estimated photon index (above 50 MeV) of  -4.7 +/- 0.7 in the time interval 0 - 20 s  after the GBM trigger. The corresponding estimated photon flux above 50 MeV is 1.1E-4 +/- 5.1E-5 ph/cm2/s. The highest-energy photon is a 200 MeV event which is observed 13 seconds after the GBM trigger.

The Fermi-LAT point of contact for this burst is Niccolo' di Lalla (<>).

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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