2002MNRAS.334..459X

The results of photometry of three gamma-ray-loud quasars, PKS 1510-089, 3C 279 and OJ248, during 2001 in the B, V and R bands and implications for the supermassive black hole (SMBH) model in these objects are presented. The results show that the three quasars had significant, but irregular, rapid outbursts with a typical time-scale of about 40-60min and a typical amplitude of about Δm ≃0.60-1.26mag during the observations. For 3C 279 and OJ248 the upper limits of the masses of SMBHs are estimated from the observed minimum optical variability time-scale, and the lower limits are also estimated by a method proposed by Dermer & Gehrels. The masses derived from both methods are reasonable. For PKS 1510-089 a new brightness minima was also observed. Analysing the observations from 1999 to 2001, three minima were observed. Although their light curves are poorly sampled, it is intriguing to note that these minimum at intervals of about 43min seem to indicate the possibility of a periodic phenomenon. So a hypothesis is proposed to interpret the phenomenon, suggesting that there is a binary black hole system at the centre. The parameters of the system are estimated by a very simple method. The periodicity is about 336±14d in the observed frame; the masses of the primary and secondary black holes are 10^8.0 and 10^6.2 M_☉, respectively; the distance between two black holes is 10^15.81 cm (378 R_g of the primary black hole), and the lifetime of the system is 10^6.0 yr. These results seem to indicate that PKS 1510-089 is another possible candidate binary black hole system. It should be monitored in future to obtain more data for further analysis to test the hypothesis.