The BL Lacertae object OJ 287 is a very unusual quasar producing a wobbling
radio jet and some double-peaked optical outbursts with a possible period of
about 12 yr for more than one century. This variability is widely explained by
models of binary supermassive black hole (SMBH) or precessing jet/disk from a
single SMBH. To enable an independent and nearly bias-free investigation on
these possible scenarios, we explored the feasibility of extremely
high-precision differential astrometry on its innermost restless jet at
mm-wavelengths. Through re-visiting some existing radio surveys and very long
baseline interferometry (VLBI) data at frequencies from 1.4 to 15.4 GHz and
performing new Very Long Baseline Array (VLBA) observations at 43.2 GHz, we
find that the radio source J0854+1959, 7.1 arcmin apart from OJ 287 and no
clearly-seen optical and infrared counterparts, could provide a nearly ideal
reference point to track the complicated jet activity of OJ 287. The source
J0854+1959 has a stable GHz-peaked radio spectrum and shows a jet structure
consisting of two discrete, mas-scale-compact and steep-spectrum components and
showing no proper motion over about 8 yr. The stable VLBI structure can be
interpreted by an episodic, optically thin and one-sided jet. With respect to
its 4.1-mJy peak feature at 43.2 GHz, we have achieved an astrometric precision
at the state-of-art level, about 10 μas. These results indicate that future
VLBI astrometry on OJ 287 could allow us to accurately locate its jet apex and
activity boundary, align its restless jet structure over decades without
significant systematic bias, and probe various astrophysical scenarios.Comment: 10 pages, 3 figures, 2 tables, accepted for publication in
Astrophysical Journal Letter