Variability analysis of X-ray spectrum of Blazar OJ 287 from Suzaku/XIS and Swift/XRT

Abstract

From optical observations, Blazar OJ 287 is known to exhibit periodic outbursts. A model of Binary Supermassive Black Holes (SMBHs) in the center of OJ 287 is used to explain the phenomenon of 12-year periodic outbursts. Multiwavelength observations confirm outbursts of OJ 287 in several bands, one of them is in the X-ray band. X-ray spectra of OJ 287 from X-ray observations in 2005 to 2016 were analyzed to determine the variability in X-ray. Spectral data were obtained from X-ray Imaging Spectrometers (XIS) from Suzaku mission and X-ray Telescope (XRT) mission from Swift. Energy intervals of the X-ray spectra are 0.4 – 10 keV for Suzaku/XIS and 0.3 – 7 keV for Swift/XRT. The data were divided into several non-outburst and outburst data groups. In general, power law model is considered the most appropriate model and it is also confirmed that the X-ray spectra of OJ 287 during that period exhibit fluctuation in photon index value, Γ. Variability of the value of Γ indicates that there is evolution of the X-ray spectra of OJ 287 during the non-outburst phase and also during the transitions between non-outburst and outburst phase and vice versa. Different values of Γ are also found during different outburst phases. In general, the derived values of Γ are in agreement with the inverse Compton process (Γ ∼1 – 2), in contrast with the synchrotron process (Γ ∼2 – 3). We also found that Γ increases as the flux increases, as opposed to synchrotron process. In addition, X-ray luminosity of OJ 287 shows fluctuation within ~1011 ≤ L⊙ ≤ 1012. The X-ray light curve was made and compared with an optical light curve to investigate the correlation of outbursts time in both bands.