A spinning supermassive black hole binary model consistent with VLBI observations of the S5 1928+738 jet

Abstract

Very Long Baseline Interferometry (VLBI) allows for high-resolution and highsensitivity observations of relativistic jets, that can reveal periodicities of several years in their structure. We perform an analysis of long-term VLBI data of the quasar S5 1928+738 in terms of a geometric model of a helical structure projected onto the plane of the sky. We monitor the direction of the jet axis through its inclination and position angles. We decompose the variation of the inclination of the inner 2 milliarcseconds of the jet of S5 1928+738 into a periodic term with amplitude of ∼ 0.89 • and a linear decreasing trend with rate of ∼ 0.05 • yr −1 . We also decompose the variation of the position angle into a periodic term with amplitude of ∼ 3.39 • and a linear increasing trend with rate of ∼ 0.24 • yr −1 . We interpret the periodic components as arising from the orbital motion of a binary black hole inspiraling at the jet base and derive corrected values of the mass ratio and separation from the accumulated 18 years of VLBI data. Then we identify the linear trends in the variations as due to the slow reorientation of the spin of the jet emitter black hole induced by the spin-orbit precession and we determine the precession period T SO = 4852 ± 646 yr of the more massive black hole, acting as the jet emitter. Our study provides indications, for the first time from VLBI jet kinematics, for the spinning nature of the jet-emitting black hole.

Structure of the nucleus of 1928+738

“…We indicate the positions of the two stationary components Cg and CS, which are associated with the two black holes of the BBH system Cg-CS, the position of the black hole BHC6, which ejected components C5, C6, and C7b, and finally, the positions of components C1, C6, and C8 whose ejections have been fitted. that we need to estimate the influence of the slow rotation of the BBH system Cg-CS around the mass ejecting C5 and C6, and we need to correct the coordinates given by Kun et al (2014) for this perturbation to obtain the precise characteristics of the BBH system Cg-CS.…”

“…The core and the jet components were fitted by circular Gaussian. For details about the error calculation and component identification see Kun et al (2014). We considered the VLBI core to be associated with component Cg; Kun et al (2014) considered that the VLBI core is associated with component CS.…”

“…For details about the error calculation and component identification see Kun et al (2014). We considered the VLBI core to be associated with component Cg; Kun et al (2014) considered that the VLBI core is associated with component CS. We therefore corrected the original coordinates of Kun et al (2014) to take into account this new origin.…”

“…2. Separation from the core for the different VLBI components obtained by Kun et al (2014) for source 1928+738 using from MOJAVE data (Lister et al 2009b). We fitted components C1, C6, and C8, which have been ejected by black holes Cg, CS, and BHC6.…”

“…To precisely determine of the characteristics of the BBH system ejecting component C8, we first found the characteristics of the BBH system Cg-CS using the coordinates of C8 given by Kun et al (2014), see Appendix A. Then we estimated the perturbation by the slow rotation of the BBH system Cg-CS around the second BBH system BHC6-BH4 assuming M BHC6 + M BH4 = (M CS + M Cg )/10 and corrected the coordinates given by Table 1.…”