Repeated pattern of gamma-ray flares in the lightcurve of the blazar 3C
  279
  The optical polarization plane of some blazars occasionally exhibits smooth
hundred degree long rotations. Multiple theoretical models have been proposed
to explain the nature of such events. A deterministic origin of these
rotations, however, remains uncertain. We aim to find repeating patterns of
flares in gamma-ray light curves of blazars, which accompany optical
polarization plane rotations. Such patterns have been predicted to occur by one
of the models explaining this phenomenon. For the blazar 3C 279, where multiple
polarization plane rotations have been reported in the literature, we obtain
the Fermi-LAT gamma-ray light curve and analyze its intervals adjacent to
polarization plane rotations. We find a complex characteristic pattern of
flares in the gamma-ray light curve that is repeated during periods adjacent to
three large amplitude EVPA rotation events in 3C 279. We discover a "hidden
EVPA rotation", which can only be seen in the relative Stokes parameters plane
and that occurred simultaneously with the fourth repetition of the pattern.
This finding strongly favors the hypothesis of emission features propagating in
the jet as the reason of optical polarization plane rotations. Furthermore, it
is compatible with the hypothesis of a sheath in the jet comprised of more
slowly propagating emission features.
