The X-ray outburst of PG 1553+113: A precession effect of two jets in the supermassive black hole binary system

Abstract

Blazar PG 1553+113 is thought to be a host of supermassive black hole binary (SMBHB) system. A 2.2-year quasi-periodicity in the $\gamma$-ray light curve was detected, possibly result of jet precession. Motivated by the previous studies based on the $\gamma$-ray data, we analyzed the X-ray light curve and spectra observed during 2012--2020. The 2.2-year quasi-periodicity might be consistent with the main-flare recurrence in the X-ray light curve. When a weak rebrightening in the $\gamma$-ray was observed, a corresponding relatively strong brightening in the X-ray light curve can be identified. The "harder-when-brighter" tendency in both X-ray main and weak flares was shown, as well as a weak "softer-when-brighter" behavior for the quiescent state. We explore the possibility that the variability in the X-ray band can be interpreted with two-jet precession scenario. Using the relation between jets and accretion discs, we derive the primary black hole mass $\simeq 3.47\times 10^8M_{\odot}$ and mass of the secondary one $\simeq 1.40\times 10^8M_{\odot}$, and their mass ratio $\sim 0.41$.