GCN Circular 27557

F. Longo (University & INFN Trieste), D.Kocesvki (NASA/MSFC),
E.Bissaldi (Politecnico and INFN, Bari), M.Ohno (Hiroshima University)
and M.Palatiello (University of Udine & INFN, Trieste)
report on behalf of the Fermi-LAT Collaboration:

On April 12, 2020, Fermi-LAT detected high-energy emission from
GRB 200412B, which was also detected by Fermi-GBM
(trigger 608375325/200412381).

The best LAT on-ground location is found to be
RA, Dec = 277.48, 61.79 (degrees, J2000)
with an error radius of 0.5 deg (90% containment, statistical error only).
This was 59 deg from the LAT boresight at the time of the GBM trigger:
T0 = 09:08:40 UT.

The data from the Fermi-LAT show a significant increase
in the event rate after the GBM trigger that is spatially correlated with the
GBM emission (2.6 degrees from the GBM position) with high significance.
The photon flux above 100 MeV in the time interval 0-1000 s after the
GBM trigger is 6.0 +/- 1.6 e-5 ph/cm2/s.

The estimated photon index above 100 MeV is -2.9 +/- 0.4

The highest-energy photon is a 1.1 GeV event which is observed 134 seconds
after the GBM trigger.

A Swift ToO has been requested for this burst.

The Fermi-LAT point of contact for this burst is
Michele Palatiello (michele.palatiello@gmail.com)

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.