Jet variability in small mass ratio supermassive black hole binaries

Abstract

We present three-dimensional general relativistic magnetohydrodynamic simulations of a precessing supermassive black hole binary with mass ratio q=1/7, embedded in a circumbinary disk. We investigate how dynamics within the binary cavity launch and shape a relativistic jet to thousands of gravitational radii. The primary black hole dominates both accretion and jet power, while the smaller black hole repeatedly crosses and shocks the inner accretion flow. These passages of the secondary drive magnetized gas alternately into the upper and lower jet funnels, producing disturbances that propagate outward as quasi-periodic outflows. Although the inner flow is perturbed twice per orbit, each jet lobe shows one dominant outflow per orbit. On longer timescales, the jet precesses, reverses its magnetic handedness, and undergoes two weak phases. The first results from a reorientation of the primary spin and is followed, after the jet recovers, by a reversal in the circulation of the projected magnetic field. The second weak phase occurs as the secondary's orbit becomes nearly coplanar with the circumbinary disk, reducing the gas and magnetic flux reaching the primary. Together, these results connect cavity dynamics to large-scale jet variability and predict a set of correlated jet signatures whose relative timing and causal ordering may provide stronger evidence for a small-mass-ratio supermassive black hole binary than any one feature alone.