The Remarkable X-ray Spectra and Variability of the Ultraluminous Weak-Line Quasar SDSS J1521+5202

TL;DR

This study investigates the extreme X-ray variability of the ultraluminous weak-line quasar SDSS J1521+5202, revealing insights into its spectral properties and supporting a model involving a thick disk and outflow causing variable absorption.

Contribution

It provides the first detailed X-ray spectral and variability analysis of SDSS J1521+5202, supporting the thick-disk plus outflow model for WLQs with new observational evidence.

Findings

X-ray flux varies by up to a factor of 32 over 17 years.

2023 spectrum shows power-law with intrinsic absorption, consistent with typical WLQ emission.

2013 spectrum indicates spectral complexity not explained by simple models.

Abstract

We present a focused X-ray and multiwavelength study of the ultraluminous weak-line quasar (WLQ) SDSS J1521+5202, one of the few X-ray weak WLQs that is amenable to basic X-ray spectral and variability investigations. J1521+5202 shows striking X-ray variability during 2006--2023, by up to a factor of $\approx 32$ in 0.5--2 keV flux, and our new 2023 Chandra observation caught it in its brightest X-ray flux state to date. Concurrent infrared/optical observations show only mild variability. The 2023 Chandra spectrum can be acceptably described by a power law with intrinsic X-ray absorption, and it reveals a nominal intrinsic level of X-ray emission relative to its optical/ultraviolet emission. In contrast, an earlier Chandra spectrum from 2013 shows apparent spectral complexity that is not well fit by a variety of models, including ionized-absorption or standard Compton-reflection models. Overall, the observations are consistent with the thick-disk plus outflow model previously advanced for WLQs, where a nominal level of underlying X-ray emission plus variable absorption lead to the remarkable observed X-ray variability. In the case of J1521+5202 it appears likely that the outflow, and not the thick disk itself, lies along our line-of-sight and causes the X-ray absorption.