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

• Main Authors: Nibedita Kalita, Alok C. Gupta, Minfeng Gu
• Format: Article
• Language: English
• Published: MDPI AG 2020-08-01
• Series: Galaxies
• Subjects: BL Lac objects; individual; OJ 287 galaxies; active-galaxies; jets-radiation mechanisms; non-thermal X-rays
• Online Access: https://www.mdpi.com/2075-4434/8/3/58

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 <i>Swift</i> satellite during September 2019–March 2020. In this period, the source showed moderate variability characterized by variability amplitude of ∼22–31% in all the wavelengths on a short timescale, except the hard X-ray band which was variable by only ∼8%. We observed that the X-ray flux of the source was significantly dominated by the soft photons below 2 keV. Soft lags of ∼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.