The bluest changing-look QSO SDSS J224113-012108

TL;DR

This paper reports a newly identified changing-look quasar, SDSS J224113-012108, exhibiting significant spectral and photometric variability, unusual spectral features, and potential links to a tidal disruption event, providing insights into quasar evolution.

Contribution

It presents the discovery and detailed analysis of a unique changing-look quasar with unprecedented spectral changes and variability, highlighting complexities in black hole mass estimates and variability mechanisms.

Findings

The quasar's broad Hα to Hβ flux ratio changed from 7 to 2.7 between 2011 and 2017.

The spectral index in 2017 is the bluest among known CLQSOs.

The black hole mass estimates differ by two orders of magnitude depending on the method.

Abstract

In this manuscript, we report a new changing-look QSO (CLQSO) SDSS J2241 at $z=0.059$. Based on the multi-epoch SDSS spectra from 2011 to 2017, the flux ratio of broad H$\alpha$ to broad H$\beta$ has been changed from 7\ in 2011 to 2.7\ in 2017, leading SDSS J2241 with spectral index $\alpha_\lambda\sim-5.21\pm0.02$ ($\lambda< 4000$\AA) in 2017 to be so-far the bluest CLQSO. Based on the SDSS spectrum in 2011, the host galaxy contributions with stellar velocity dispersion $\sim86{\rm km/s}$ can be well determined, leading to the M-sigma relation expected central BH mass $\sim3\times10^6{\rm M_\odot}$. However, through properties of the broad H$\alpha$, the virial BH mass is $\sim10^8{\rm M_\odot}$, about two magnitudes larger than the mass through the M-sigma relation. The different BH masses through different methods indicate SDSS J2241 is one unique CLQSO. Meanwhile, the long-term photometric light curve shows interesting variability properties, not expected by DRW process commonly applied in AGN but probably connected to a central TDE. Furthermore, based on continuum emission properties in 2017 with no dust obscurations, only considering the moving dust clouds cannot be preferred to explain the CLQSO SDSS J2241, because the expected intrinsic reddening corrected continuum emissions were unreasonably higher than the unobscured continuum emissions in 2017.