XMM observations of BAL Quasars with polar outflows

TL;DR

This study investigates X-ray properties of polar BAL quasars with radio variations, finding some are X-ray normal without absorption, while others show signs of strong intrinsic X-ray absorption, challenging existing models.

Contribution

First X-ray observations of polar BAL quasars reveal diverse absorption characteristics, suggesting the absence of shielding gas in some polar outflows and indicating complex absorption scenarios.

Findings

Two sources are X-ray normal with no intrinsic absorption.

One FeLoBAL shows significant X-ray weakness, indicating strong absorption.

X-ray properties vary, challenging uniform models of BAL outflows.

Abstract

We have selected a sample of broad absorption line (BAL) quasars which show significant radio variations, indicating the presence of polar BAL outflows. We obtained snapshot XMM observations of four polar BAL QSOs, to check whether strong X-ray absorption, one of the most prominent characteristics of most BAL QSOs, also exist in polar outflows. Two of the sources are detected in X-ray. Spectral fittings show that they are X-ray normal with no intrinsic X-ray absorption, suggesting the X-ray shielding gas might be absent in polar BAL outflows. Comparing to non-BAL QSOs, one of two X-ray nondetected sources remains consistent with X-ray normal, while the other one, which is an iron low-ionization BAL (FeLoBAL), shows an X-ray weakness factor of > 19, suggesting strong intrinsic X-ray absorption. Alternative explanations to the nondetection of strong X-ray absorption in the two X-ray detected sources are 1) the absorption is more complex than a simple neutral absorber, such as partial covering absorption or ionized absorption; 2) there might be significant jet contribution to the detected X-ray emission. Current data is insufficient to test these possibilities, and further observations are required to understand the X-ray nature of polar BAL outflows.