  We search the Fermi-LAT photon database for an extended gamma-ray emission
which could be associated with any of the 581 previously detected gamma-ray
bursts (GRBs) visible to the Fermi-LAT. For this purpose we compare the number
of photons with energies E > 100 MeV and E > 1 GeV which arrived in the first
1500 seconds after the burst from the same region, to the expected background.
We require that the expected number of false detections does not exceed 0.05
for the entire search and find the high-energy emission in 19 bursts, four of
which (GRB 081009, GRB 090720B, GRB 100911 and GRB 100728A) were previously
unreported. The first three are detected at energies above 100 MeV, while the
last one shows a statistically significant signal only above 1 GeV.
