Gamma-ray emission region located in the parsec scale jet of OJ287
  We report on the location of the gamma-ray emission region in flares of the
BL Lacertae object OJ287 at >14pc from the central supermassive black hole. We
employ data from multi-spectral range (total flux and linear polarization)
monitoring programs combined with sequences of ultra-high-resolution 7mm VLBA
images. The correlation between the brightest gamma-ray and mm flares is found
to be statistically significant. The two gamma-ray peaks, detected by
Fermi-LAT, that we report here happened at the rising phase of two
exceptionally bright mm flares accompanied by sharp linear polarization peaks.
The VLBA images show that these mm flares in total flux and polarization degree
occurred in a jet region at >14pc from the innermost jet region. The time
coincidence of the brighter gamma-ray flare and its corresponding mm linear
polarization peak evidences that both the gamma-ray and mm outbursts occur
>14pc from the central black hole. We find two sharp optical flares occurring
at the peak times of the two reported gamma-ray flares. This is interpreted as
the gamma-ray flares being produced by synchrotron self-Compton scattering of
optical photons from the flares triggered by the interaction of moving knots
with a stationary conical shock in the jet.
