GRB 220228A: Fermi-LAT detection

On February 28, 2022, Fermi-LAT detected high-energy emission from GRB 220228A, which was also detected by**Fermi-GBM (trigger 667737010 / 220228438, GCN 31658). The best LAT on-ground location is found to be RA, Dec = 311.2, -22.7 (degrees, J2000) with an error radius of 0.7 deg (90 % containment, statistical error only). This was 23 deg from the LAT boresight at the time of the trigger: T0 = 10:30:05.92 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 90 MeV in the time interval 0-1000s after the GBM trigger is 4E-6 ± 1E-6 ph/cm2/s. The estimated photon index above 90 MeV is -2.9 ± 0.4. The highest-energy photon is a 323 MeV**event which is observed 77 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.