Optical multi-color monitoring of OJ 287 from 2006 to 2012

Abstract

We present our opticalmulti-colormonitoring of the BL Lac object OJ 287 from January 2006 to December 2012 in the V, R and I bands. A relatively active state in OJ 287 has been found over all monitored epochs, among which the variations of average magnitude in V/R/I bands were measured with ΔV = 1.956 mag, ΔR = 2.067 mag and ΔI = 2.115mag, respectively. No reliable intraday variability is detected, but possible variability is detected on 16 nights. Their relative variation amplitudes fall into the range between 1% and 8%, with the majority between 2% and 4%. No time lags have been detected, but strong correlations exist among light curves in the three wavebands. The bluer-when-brighter trend is dominant over intraday timescales, which supports the shock-in-jet model. When combining with additional V/R band data obtained from SMARTS and the Steward Observatory, we also find a bluer-when-brighter trend over a long-term timescale. Some possible periods of 513, 176, 36, 30, 26, 17 and 14 d are found in all time-series data sets from 2006 to 2017. Possible explanations about these periods are given.