New jet feature in the parsec-scale jet of the blazar OJ287 connected to
  the 2017 teraelectronvolt flaring activity
  In February 2017 the blazar OJ287, one of the best super-massive
binary-black-hole-system candidates, was detected for the first time at very
high energies (VHEs; E>100GeV) with the ground-based gamma-ray observatory
VERITAS. Very high energy gamma rays are thought to be produced in the near
vicinity of the central engine in active galactic nuclei. For this reason, and
with the main goal of providing useful information for the characterization of
the physical mechanisms connected with the observed teraelectronvolt flaring
event, we investigate the parsec-scale source properties by means of
high-resolution very long baseline interferometry observations. We use 86 GHz
Global Millimeter-VLBI Array (GMVA) observations from 2015 to 2017 and combine
them with additional multiwavelength radio observations at different
frequencies from other monitoring programs. We investigate the source structure
by modeling the brightness distribution with two-dimensional Gaussian
components in the visibility plane. In the GMVA epoch following the source VHE
activity, we find a new jet feature (labeled K) at about 0.2 mas from the core
region and located in between two quasi-stationary components (labeled S1 and
S2). Multiple periods of enhanced activity are detected at different radio
frequencies before and during the VHE flaring state. Based on the findings of
this work, we identify as a possible trigger for the VHE flaring emission
during the early months of 2017 the passage of a new jet feature through a
recollimation shock (represented by the model-fit component S1) in a region of
the jet located at a de-projected distance of about 10 pc from the radio core.
