A century of change: new changing-look event in Mrk 1018's past

TL;DR

This study analyzes over a century of data on Mrk 1018, revealing a historic outburst and suggesting long-term accretion rate modulation as the cause of its changing-look behavior, with rapid recent transitions.

Contribution

It uncovers a historic outburst in Mrk 1018 and proposes a long-term modulation mechanism, advancing understanding of changing-look AGN variability.

Findings

Historic outburst between 1935-1960 with ~0.8 mag variation

Broad periodicity of 29-47 years suggested by Lomb-Scargle analysis

Recent turn-off duration constrained to less than 1.9 years

Abstract

We investigate the long-term variability of the known Changing Look Active Galactic Nuclei (CL AGN) Mrk 1018, whose second change we discovered as part of the Close AGN Reference Survey (CARS). Collating over a hundred years worth of photometry from scanned photographic plates and five modern surveys we find a historic outburst between ~1935-1960, with variation in Johnson B magnitude of ~0.8 that is consistent with Mrk 1018's brightness before and after its latest changing look event in the early 2010s. Using the combined modern and historic data, a Generalised Lomb-Scargle suggests broad feature with P = 29-47 years. Its width and stability across tests, as well as the turn-on speed and bright phase duration of the historic event suggests a timescale associated with long-term modulation, such as via rapid flickering in the accretion rate caused by the Chaotic Cold Accretion model rather than a strictly periodic CL mechanism driving changes in Mrk 1018. We also use the modern photometry to constrain Mrk 1018's latest turn-off duration to less than ~1.9 years, providing further support for a CL mechanism with rapid transition timescales, such as a changing mode of accretion.