  Blazars emit a highly-variable non-thermal spectrum. It is usually assumed
that the same non-thermal electrons are responsible for the IR-optical-UV
emission (via synchrotron) and the gamma-ray emission (via inverse Compton).
Hence, the light curves in the two bands should be correlated. Orphan gamma-ray
flares (i.e., lacking a luminous low-frequency counterpart) challenge our
theoretical understanding of blazars. By means of large-scale two-dimensional
radiative particle-in-cell simulations, we show that orphan gamma-ray flares
may be a self-consistent by-product of particle energization in turbulent
magnetically-dominated pair plasmas. The energized particles produce the
gamma-ray flare by inverse Compton scattering an external radiation field,
while the synchrotron luminosity is heavily suppressed since the particles are
accelerated nearly along the direction of the local magnetic field. The ratio
of inverse Compton to synchrotron luminosity is sensitive to the initial
strength of turbulent fluctuations (a larger degree of turbulent fluctuations
weakens the anisotropy of the energized particles, thus increasing the
synchrotron luminosity). Our results show that the anisotropy of the
non-thermal particle population is key to modeling the blazar emission.
