The ever-surprising blazar OJ 287: multi-wavelength study and appearance
  of a new component in X-rays
  We present a multi-wavelength spectral and temporal investigation of OJ 287
emission during its strong optical-to-X-ray activity between July 2016 - July
2017. The daily $\gamma$-ray fluxes from \emph{Fermi}-LAT are consistent with
no variability. The strong optical-to-X-ray variability is accompanied by a
change in power-law spectral index of the X-ray spectrum from $< 2$ to $>2$,
with variations often associated with changes in optical polarization
properties. Cross-correlations between optical-to-X-ray emission during four
continuous segments show simultaneous optical-ultraviolet (UV) variations while
the X-ray and UV/optical are simultaneous only during the middle two segments.
In the first segment, the results suggest X-rays lag the optical/UV, while in
the last segment X-rays lead by $\sim$ 5-6 days. The last segment also shows a
systematic trend with variations appearing first at higher energies followed by
lower energy ones. The LAT spectrum before the VHE activity is similar to
preceding quiescent state spectrum while it hardens during VHE activity period
and is consistent with the extrapolated VHE spectrum during the latter.
Overall, the broadband spectral energy distributions (SEDs) during high
activity periods are a combination of a typical OJ 287 SED and an HBL SED, and
can be explained in a two-zone leptonic model, with the second zone located at
parsec scales, beyond the broad line region, being responsible for the HBL-like
spectrum. The change of polarization properties from systematic to chaotic and
back to systematic, before, during and after the VHE activity, suggest dynamic
roles for magnetic fields and turbulence.
