Correlation between optical and γ-ray flux variations in BL Lacs

ABSTRACT We report here results of the analysis correlated flux variations between optical and GeV γ-ray bands in three bright BL Lac objects, namely AO 0235+164, OJ 287, PKS 2155−304. This was based on about 10 yr data from Fermi Gamma-ray Space Telescope covering period 2008 August 8 2018 along with same period. For all sources, during flares analysed this work, are found to be closely correlated. From broad-band spectral energy distribution modelling different epochs these sources using one-zone leptonic emission model, we that optical–ultraviolet is dominated by synchrotron jet. The low peaked 0235+164 287 well fitted external Compton (EC) component, while high source 2155−304 self-Compton component. Further, note high-flux state (epochs A B) requires seed photons both dusty torus broad-line region, C D can modelled EC scattering infrared torus.