# Understanding extreme quasar optical variability with CRTS: II. Changing-state quasars

## TL;DR

This study systematically identifies and characterizes 'Changing-State' quasars exhibiting significant optical and spectroscopic variability over a decade, revealing insights into their luminosity, spectral changes, and underlying accretion disk physics.

## Contribution

It introduces a new sample of high-luminosity Changing-State quasars with detailed variability analysis, extending the redshift range and comparing them to existing Changing-Look AGN.

## Key findings

- CSQs show larger photometric variability than CLQs.
- Spectroscopic variability is marginally stronger in CSQs.
- The population is linked to changes in the Eddington ratio and disk heating/cooling fronts.

## Abstract

We present the results of a systematic search for quasars in the Catalina Real-time Transient Survey exhibiting both strong photometric and spectroscopic variability over a decadal baseline. We identify 73 sources with specific patterns of optical and mid-IR photometric behavior and a defined spectroscopic change. These "Changing-State" quasars (CSQs) form a higher luminosity sample to complement existing sets of "Changing-Look" AGN and quasars in the literature. The CSQs (by selection) exhibit larger photometric variability than the CLQs. The spectroscopic variability is marginally stronger in the CSQs than CLQs as defined by the change in H$\beta$/[OIII] ratio. We find 36 sources with declining H$\beta$ flux, 37 sources with increasing H$\beta$ flux and discover seven sources with $z > 0.8$, further extending the redshift arm. Our CSQ sample compares to the literature CLQ objects in similar distributions of H$\beta$ flux ratios and differential Eddington ratios between high (bright) and low (dim) states. Taken as a whole, we find that this population of extreme varying quasars is associated with changes in the Eddington ratio and the timescales imply cooling/heating fronts propagating through the disk.