  The current version of the Fermi Large Area Telescope data (P8R2) has been
publicly available since June 2015, with the caveat that the residual
background of all event classes, except ULTRACLEANVETO, was not fully
isotropic: it was enhanced by a factor ~2 at 1-3 GeV within ~20 deg of the
Ecliptic compared to the poles. By investigating the residual background using
data only, we were able to find two sources of residual background: one due to
non-interacting heavy ions and one due to cosmic-ray electrons leaking through
the ribbons of the Anti-Coincidence Detector, the latter source being
responsible for the background anisotropy. A set of simple cuts allows us to
reject these events while losing less than 1% of the SOURCE class acceptance.
This new selection has been used to produce a new version of the LAT data
(P8R3).
