Temporal and Spectral Variability of OJ 287 before the April--June 2020 Outburst

Abstract

We present the results of a temporal and spectral study of the BL Lacertae object OJ 287 in optical, UV, and X-ray bands with observations performed by Swift satellite during September 2019--March 2020. In this period, the source showed moderate variability characterized by variability amplitude of $\sim$22--31% in all the wavelengths on a short timescale, except the hard X-ray band which was variable by only $\sim$8%. We observed that the X-ray flux of the source was significantly dominated by the soft photons below $2$ keV. Soft lags of $\sim$45 days were detected between the optical/UV and soft X-ray emissions, while there is no correlation between the hard X-rays and the lower energy bands indicating the presence of two emission components or electron populations. Although two components contribute to the X-ray emission, most of the 0.3--10 keV spectra were well fitted with an absorbed power-law model which outlines the dominance of synchrotron over inverse Compton (IC) mechanism. The X-ray spectra follow a weak "softer when brighter" trend.

11 pages, 4 figures, published in the special issue "X-Ray Flux and Spectral Variability of Blazars" of Galaxies journal

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• The First Swift Ultra-Violet/Optical Telescope GRB Afterglow Catalog
• Chi-square and Poissonian Data: Biases Even in the High-Count Regime and How to Avoid them
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• X-ray emission of radio-loud quasar SDSS J121426.52+140258.9: independent variations between optical/UV and X-ray emission