Black hole mass and binary model for BL Lac object OJ 287
  Recent intensive observations of the BL Lac object OJ 287 raise a lot of questions on the models of binary black holes, processing jets, rotating helical jets and thermal instability of slim accretion disks. After carefully analyzing their radio flux and polarization data, Valtaoja et al. (\cite{valtaoja00}) propose a new binary model. Based on the black hole mass of $4 \times 10^8 {\rm M_\odot}$ estimated with the tight correlations of the black hole masses and the bulge luminosity or central velocity dispersion of host galaxies, we computed the physical parameters of the new binary scenario. The impact of the secondary on the accretion disk around the primary black hole causes strong shocks propagating inwards and outwards, whose arrival at the jet roots is identified with the rapid increase of optical polarization and the large change of polarization angle at about 0.30 yr after the first main optical flare. An increase of optical polarization, a large rotation of positional angle and a small synchrotron flare at 2007.05 between the optical outbursts at 2006.75 and 2007.89 are expected by the model. With the estimated parameters, we predicated an increase of $\gamma$-ray flux appearing about 5 days after the first optical/IR peak, which is consistent with the EGRET observations. 
F.K. Liu (1,2) and Xue-Bing Wu (2) ((1) Chalmers University of   Technology, Sweden (2) Peking University, China)