A Mid-IR Selected Changing-Look Quasar and Physical Scenarios for Abrupt AGN Fading

TL;DR

This paper reports the discovery of a changing-look quasar with significant mid-IR and X-ray fading, showing the disappearance of broad emission lines and suggesting accretion disk changes as the likely cause.

Contribution

The study presents a newly identified changing-look quasar with multiwavelength observations, providing insights into physical scenarios behind abrupt AGN fading, especially emphasizing accretion disk changes.

Findings

The quasar WISE J1052+1519 faded by over a factor of two in mid-IR and at least fifteen in soft X-rays.

Spectroscopy shows the broad Hβ emission vanished, and the quasar became redder.

Mid-IR data strongly disfavor obscuration as the cause of the fading.

Abstract

We report a new changing-look quasar, WISE~J105203.55+151929.5 at $z=0.303$, found by identifying highly mid-IR variable quasars in the WISE/NEOWISE data stream. Compared to multi-epoch mid-IR photometry of a large sample of SDSS-confirmed quasars, WISE J1052+1519 is an extreme photometric outlier, fading by more than a factor of two at $3.4$ and $4.6 \mu$m since 2009. Swift target-of-opportunity observations in 2017 show even stronger fading in the soft X-rays compared to the ROSAT detection of this source in 1995, with at least a factor of fifteen decrease. We obtained second-epoch spectroscopy with the Palomar telescope in 2017 which, when compared with the 2006 archival SDSS spectrum, reveals that the broad H$\beta$ emission has vanished and that the quasar has become significantly redder. The two most likely interpretations for this dramatic change are source fading or obscuration, where the latter is strongly disfavored by the mid-IR data. We discuss various physical scenarios that could cause such changes in the quasar luminosity over this timescale, and favor changes in the innermost regions of the accretion disk that occur on the thermal and heating/cooling front timescales. We discuss possible physical triggers that could cause these changes, and predict the multiwavelength signatures that could distinguish these physical scenarios.