  Blazars are a subclass of active galactic nuclei (AGN) having relativistic
jets aligned within a few degrees of our line-of-sight and form the majority of
the AGN detected in the TeV regime. The Fermi-Large Area Telescope (LAT) is a
pair-conversion telescope, sensitive to photons having energies between 20 MeV
and 2 TeV, and is capable of scanning the entire gamma-ray sky every three
hours. Despite the remarkable success of the Fermi mission, many questions
still remain unanswered, such as the site of gamma-ray production and the
emission mechanisms involved. The Asteroid Terrestrial-impact Last Alert System
(ATLAS) is a high cadence all sky survey system optimized to be efficient for
finding potentially dangerous asteroids, as well as in tracking and searching
for highly variable and transient sources, such as AGN. In this study, we
investigate possible correlations between the Fermi-LAT observations in the 100
MeV-300 GeV energy band and the ATLAS optical data in the R-band, centered at
679 nm, for a sample of 18 TeV-detected northern blazars over 8 years of
observations between 2015 and 2022. Under the assumption that the optical and
gamma-ray flares are produced by the same outburst propagating down the jet,
the strong correlations found for some sources suggest a single-zone leptonic
model of emission.
