M. Kovacevic (INFN Perugia), D. Tak (Univ. of Maryland & NASA/GSFC),
F. Longo (University and INFN, Trieste),
M. Arimoto (Kanazawa Univ.), and M. Axelsson (KTH and Stockholm Univ.)
report on behalf of the Fermi-LAT team:
On July 27, 2019, Fermi-LAT detected high-energy emission from
GRB 190727B, which was also detected by Fermi-GBM (Veres et al., GCN
25180) and Swift-BAT (Lien et al., GCN 25176).
The best LAT on-ground location is found to be
RA, Dec 126.19, -13.34 (degrees, J2000)
with an error radius of 0.28 deg (90% containment, statistical error only).
This was 46 deg from the LAT boresight at the time of the GBM trigger:
T0 = 20:17:56.45 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 with high significance.
The photon flux above 100 MeV in the time interval 0-1500 s after the
GBM trigger is (3.15 +/- 1.25)E-6 ph/cm2/s.
The highest-energy photon in this interval is a 2.2 GeV event observed
at T0 + 345 s.
The estimated photon index above 100 MeV is -2.3 +/- 0.4.
The Fermi-LAT point of contact for this burst is Milos Kovacevic
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.