Abstract
We present long-term optical multi-band photometric monitoring of the blazar OJ 287 from 6 March 2010 to 3 April 2016, with high temporal resolution in the V R I -bands. The flux variations and colour-magnitude variations on long and short timescales were investigated to understand the emission mechanisms. In our observation, the major outbursts occurred in January 2016, as predicted by the binary pair of black holes model for OJ 287, with F v a r of 1.3∼2.1%, and variability amplitude (Amp) of 5.8∼9.0%. The intra-night variability (IDV) durations were from 18.5 to 51.3 min, and the minimal variability timescale was about 4.7 min. The colour-magnitude variation showed a weak positive correlation on the long timescale with Pearson’s r = 0 . 450 , while a negative correlation was found on intra-night timescales. We briefly discuss the possible physical mechanisms that are most likely to be responsible for the observed flux and colour-magnitude correlation variability.
Highlights
BL Lacertae (BL Lac) objects, which have either very weak or no emission lines [1], and flatspectrum radio quasars (FSRQs) with strong emission lines [2,3] form a subclass of radio-loud active galactic nuclei (AGNs) known as blazars
Blazars, being dominated by a relativistic jet oriented at a small angle from the line of sight, display variability ranging from a few hundredths of a magnitude to more than several magnitudes
Their variability timescales range from minutes to years
Summary
BL Lacertae (BL Lac) objects, which have either very weak or no emission lines [1], and flatspectrum radio quasars (FSRQs) with strong emission lines [2,3] form a subclass of radio-loud active galactic nuclei (AGNs) known as blazars. Blazars are characterised by non-thermal emission, and strong and rapid flux variability across the entire electromagnetic spectrum, from radio- to gamma-rays. Sillanpää et al [12] pointed out for the first time that there is a double-peak structure in the cyclic optical outbursts of OJ 287 by using the optical V-band observations starting from 1890. Reported the double-peak outburst occurrence in 1994–1995, which occurred almost exactly at the predicted times. These predicted recurrences are usually interpreted as OJ 287 housing a binary pair of black holes system with a period of ∼12 years. Along with the confirmation of this predicted outburst during 2015–2016 reported by [10,17], we study the properties of variability and spectral variation in a short timescales
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