Magnetic flux inversion in a peculiar changing look AGN

We argue that the changing-look event in the active galactic nucleus (AGN) IFS 1927+654, followed by a dip of three 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 disc (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 disc. 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. We find that the observed time-scale between the beginning of the changing-look event and the minimum in the X-ray luminosity, approximate to 200 d, is in agreement with the time needed to cancel the magnetic flux in a MAD extending to approximate to 180 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 suggest that similar events may lead to jet interruptions in radio-loud objects.

Automated summary

In this study, it is proposed that the changing-look event and the dip in X-ray luminosity in the active galactic nucleus are controlled by changes in accretion rate and magnetic flux inversion. While flux inversion events are rare, they may lead to observed changing-look events in AGN with unusually high X-ray to UV luminosity ratios, with a single advection event potentially causing such a flux inversion.