Sensitive Chandra coverage of a representative sample of weak-line quasars: revealing the full range of X-ray properties

TL;DR

This study uses deep Chandra X-ray observations to explore the full range of X-ray properties in weak-line quasars, revealing variability and supporting the thick disk and outflow model with diverse absorption characteristics.

Contribution

It provides the first comprehensive X-ray analysis of a representative WLQ sample, demonstrating variability and supporting the TDO model with detailed absorption estimates.

Findings

Only 5 of 32 WLQs remain X-ray undetected after observations.

SDSS J1539+3954 shows dramatic X-ray variability within ~3 months.

The TDO model explains the X-ray properties with a covering factor of ~0.5 and variable column densities.

Abstract

We present deeper Chandra observations for weak-line quasars (WLQs) in a representative sample that previously had limited X-ray constraints, and perform X-ray photometric analyses to reveal the full range of X-ray properties of WLQs. Only 5 of the 32 WLQs included in this representative sample remain X-ray undetected after these observations, and a stacking analysis shows that these 5 have an average X-ray weakness factor of > 85. One of the WLQs in the sample that was known to have extreme X-ray variability, SDSS J1539+3954, exhibited dramatic X-ray variability again: it changed from an X-ray normal state to an X-ray weak state within ~ 3 months in the rest frame. This short timescale for an X-ray flux variation by a factor of $\gtrsim$ 9 further supports the thick disk and outflow (TDO) model proposed to explain the X-ray and multiwavelength properties of WLQs. The overall distribution of the X-ray-to-optical properties of WLQs suggests that the TDO has an average covering factor of the X-ray emitting region of ~ 0.5, and the column density of the TDO can range from $N_{\rm H}$ $\sim 10^{23-24}~{\rm cm}^{-2}$ to $N_{\rm H}$ $\gtrsim 10^{24}~{\rm cm}^{-2}$, which leads to different levels of absorption and Compton reflection (and/or scattering) among WLQs.