X-ray spectra reveal the reawakening of the repeat changing-look AGN NGC 1566

TL;DR

This study presents simultaneous X-ray observations of the changing-look AGN NGC 1566 during its outburst, revealing rapid accretion disk development, a launched outflow, and photoionised emission, supporting a disk instability origin.

Contribution

The paper provides the first simultaneous broad-band X-ray spectra during an outburst of NGC 1566, demonstrating rapid disk changes and outflow features, and suggests disk instability as the cause.

Findings

Broad-band spectrum typical of Seyfert 1 AGN during outburst

Detection of a ~500 km/s outflow and photoionised emission lines

Rapid development of a standard accretion disk during the outburst

Abstract

We present simultaneous XMM-Newton and NuSTAR observations of the repeat changing-look AGN NGC 1566, which dramatically increased in brightness in the IR to X-ray bands in 2018. The broad-band X-ray spectrum was taken at the peak of the outburst and is typical of Seyfert 1 AGN. The spectrum shows a soft excess, Compton hump, warm absorption and reflection, ruling out tidal disruption as the cause of the outburst and demonstrating that a 'standard' accretion disk can develop very rapidly. The high resolution grating spectrum reveals that the outburst has launched a ~ 500 km/s outflow, and shows photoionised emission lines from rest-frame gas. We discuss possible mechanisms for the outburst, and conclude that it is most likely caused by a disk instability.