Extraordinary activity in the BL Lacertae object OJ 287

We use a continuous wavelet transform to analyze more than two decades of d ata for the BL Lac object OJ 287 acquired as part of the University of Mich igan Radio Astronomy Observatory (UMRAO) variability program. We find clear evidence for a persistent modulation of the total flux and polarization wi th period similar to 1.66 yr and for another signal that dominates activity in the 1980s with period similar to 1.12 yr. The relationship between thes e two variations can be understood in terms of a "shock-in-jet" model, in w hich the longer timescale periodicity is associated with an otherwise quies cent jet and the shorter timescale activity is associated with the passage of a shock. The different periodicities of these two components may reflect different internal conditions of the two how domains leading to different wave speeds or different contractions of a single underlying periodicity du e to the different Doppler factors of the two flow components. We suggest t hat the modulation arises from a wave driven by some asymmetric disturbance close to the central engine. The periodic behavior in polarization exhibit s excursions in U that correspond to a direction similar to 45 degrees from the VLBI jet axis. This behavior is not explained by the random walk in th e Q-U plane that is expected from models in which a pattern of randomly ali gned magnetic field elements propagate across the visible portion of the fl ow and suggests a small amplitude, cyclic variation in the flow direction i n that part of the flow that dominates centimeter wavelength emission.