Magnetic flux inversion in a peculiar changing look AGN

TL;DR

This paper proposes that the changing-look event in the AGN 1ES 1927+654 is caused by magnetic flux inversion in a magnetically arrested disk, leading to significant luminosity changes and possibly jet interruptions.

Contribution

It introduces a magnetic flux inversion model in MADs to explain changing-look phenomena and matches observed timescales with theoretical predictions.

Findings

Magnetic flux inversion can cause large luminosity dips in AGN.

The observed 200-day timescale aligns with flux cancellation in MADs.

Flux inversion events may be linked to jet interruptions in radio-loud AGN.

Abstract

We argue that the changing-look event in the active galactic nucleus 1ES 1927+654, followed by a dip of 3 orders of magnitude in the X-ray luminosity, is controlled by a change in the accretion rate and an inversion of magnetic flux in a magnetically arrested disk (MAD). Before the changing-look event, strong magnetic flux on the black hole powers X-ray emission via the Blandford-Znajek process while the UV emission is produced by a radiatively inefficient magnetized disk. An advection event, bringing flux of the opposite polarity, propagates inward leading, first, to a rise in the UV/optical luminosity and, then, to a dip in the X-ray luminosity when it reaches the black hole. We estimate the timescale for magnetic flux advection and find that the observed timescale between the beginning of the changing-look event and the minimum in the X-ray luminosity, $\approx200$ days, is in agreement with the time needed to cancel the magnetic flux in a MAD extending to $\approx180\:r_g$. Although flux inversion events might be rare due to the large ratio of flux-to-mass that is needed, we argue that AGN showing an unusually high ratio of X-ray to UV luminosity are prime candidates for such events. We also suggest that similar events may lead to jet interruptions in radio-loud objects.