SIMBAD references

This paper studies the color behavior of the BL Lac object OJ 287 during an optical outburst. Upon revisiting the data from the OJ 94 monitoring project, and from an analysis of the data obtained with the 60/90 cm Schmidt Telescope of NAOC, we found a bluer-when-brighter chromatism in this object. The amplitude of variation tends to decrease with frequency. These results are consistent with the shock-in-jet model. We ran some simulations and confirmed that both amplitude difference and time delay between variations at different wavelengths can result in the bluer-when-brighter phenomenon. Our observations confirmed that OJ 287 underwent a double-peaked outburst about 12 years after 1996, which provides further evidence for the binary black hole model in this object.