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

Abstract

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 . The X-ray light curve was made and compared with an optical light curve to investigate the correlation of outbursts time in both bands.

X-ray spectral variability of blazars using principal component analysis

“…This can be used to distinguish between emission mechanisms in blazars. Blazars are known to emit in the X-ray through either synchrotron emission, the inverse Compton effect, or some combination of both according to their luminosity (Donato, 2001), and correlations between Γ and flux are indicative of inverse Compton emission (Fatima, 2017). A decrease in the first principal component with energy can therefore be used as an indicator of Comptonization.…”

“…Its long-term PCA (Figure 3) can be explained by correlated variations in Γ and normalization (compare to the third panel in Figure 6, and see the discussion of it in Section 5). Fatima (2017) remarks that OJ 287 is known to emit via the inverse Compton process.…”

“…Enforcing a correlation between normalization and Γ is not without precedent, and in fact seems to be the case for OJ 287 in particular. Fatima (2017) finds such a correlation, and remarks that this indicates inverse Compton emission rather than the synchrotron process.…”