Distortion of a relativistic jet echoing a magnetic flux eruption

TL;DR

This paper investigates how episodic magnetic flux eruptions in magnetically saturated black hole accretion systems distort relativistic jets, affecting their structure and observable properties.

Contribution

It provides the first detailed analysis of jet distortion mechanisms caused by magnetic flux eruptions using high-resolution 3D GRMHD simulations.

Findings

Eruptions cause strong helical distortions in jets.

Toroidal magnetic fields form poloidal bypasses during eruptions.

Jet re-accumulation leads to tilted jet sections affecting radiation observations.

Abstract

Magnetized accretion onto spinning black holes can accumulate a large magnetic flux across the event horizon and launch a pair of relativistic jets via the Blandford-Znajek mechanism. In the magnetically saturated (arrested) state, excess magnetic flux is ejected from the black hole in episodic magnetic flux eruptions, which result in a significant yet temporary reduction of jet power. We analyze results of a high-resolution 3D general-relativistic magneto-hydro-dynamic numerical simulation of geometrically thick magnetically saturated accretion onto a high-spin Kerr black hole for a single cycle of magnetic flux eruption and accumulation. We show that following an eruption, a weakened jet develops a strong helical distortion with distinct structure of magnetic fields - the poloidal field along the jet core is unaffected by the eruption; while toroidal field lines, ejected from the black hole during the eruption and later re-advected onto it, form poloidal `bypasses' along the inner jet sheath. Such a distortion may appear in sources fed by geometrically thick accretion flows as an asymmetric superluminal knot, strongly interacting with the jet sheath along an oblique working surface. The jet section re-powered by magnetic flux re-accumulated on the black hole is tilted by a few degrees, implying significant variations in radiation boost towards observers of BL Lac blazars. The intrinsic structure of the jet spine is consistent with axisymmetric semi-analytical models.