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

中文翻译：

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BL Lacs中光学和γ射线通量变化之间的相关性

我们在这里报告了三个明亮的 BL Lac 天体（即 AO 0235+164、OJ 287 和 PKS 2155-304）中光学和 GeV γ 射线带之间相关通量变化的分析结果。这是基于对费米伽马射线太空望远镜 2008 年 8 月 8 日至 2018 年 8 月 8 日期间大约 10 年的数据以及同一时期的光学数据的分析。对于所有源，在这项工作中分析的耀斑期间，发现光学和 γ 射线通量变化密切相关。通过使用单区轻子发射模型对这些源中不同时期的宽带光谱能量分布建模，我们发现光学 - 紫外线发射主要由射流的同步加速器发射。发现低同步加速器峰值源 AO 0235+164 和 OJ 287 中的 γ 射线发射与外部康普顿 (EC) 分量很好地拟合，而高同步加速器峰值源 PKS 2155-304 中的 γ 射线发射很好装有同步加速器自康普顿组件。此外，我们注意到 AO 0235+164（时期 A 和 B）的高通量状态期间的 γ 射线发射需要来自尘埃环面和宽线区域的种子光子，而 OJ 287 中的 γ 射线发射在 AO 0235+164 的 C 和 D 时期，可以通过来自环面的红外光子的 EC 散射来模拟。