A Detailed Look at a Trio of Changing-Look Quasars: Spectral Energy Distributions and the Dust Extinction Test

TL;DR

This study investigates three changing-look quasars using multi-epoch spectra to determine the cause of their dramatic variability, finding that intrinsic luminosity changes, rather than dust obscuration, drive their state transitions, likely due to altered accretion flows.

Contribution

The paper provides the first detailed spectral energy distribution analysis of changing-look quasars in low states, strongly supporting intrinsic luminosity changes over dust obscuration as the cause.

Findings

Dust obscuration is unlikely to explain the variability.

Low-state spectra resemble low-luminosity AGN.

Transitions may be driven by changes in accretion flow structure.

Abstract

Changing-look quasars exhibit dramatic variability in broad emission-line fluxes on short timescales. This behavior is challenging to many models of the quasar broad line region, due in large part to the short transition times between high and low states. In order to constrain the cause of the dramatic variability, we obtained contemporaneous Hubble Space Telescope UV and Hobby Eberly Telescope optical spectra of three changing-look quasars caught in their low state. We use these spectra, along with archival spectra taken during both the high and low states, to investigate potential scenarios for the change in state. Our data strongly disfavor a variable dust obscuration scenario for these three CLQs, and instead suggest that the observed transformation reflects a change in the intrinsic luminosity of the central engine. We also find that the low-state spectral energy distributions of all three quasars are reminiscent of those of low-luminosity active galactic nuclei, which suggests that the transition may result from a change in accretion flow structure caused by a reduced Eddington ratio.