Broad Iron Emission from Gravitationally Lensed Quasars Observed by Chandra

TL;DR

This study analyzes 27 gravitationally lensed quasars with Chandra, revealing a common broad iron emission component from the inner accretion disk, which can help measure black hole spins at high redshift.

Contribution

It provides the first evidence of a broad iron emission component in a large sample of high-redshift lensed quasars, indicating potential for high-redshift black hole spin measurements.

Findings

Detection of a significant broad iron emission component with >3-sigma confidence.

Most quasars show a narrow iron core similar to local AGN.

The broad component suggests widespread inner disk emission in high-redshift quasars.

Abstract

Recent work has demonstrated the potential of gravitationally lensed quasars to extend measurements of black hole spin out to high-redshift with the current generation of X-ray observatories. Here we present an analysis of a large sample of 27 lensed quasars in the redshift range 1.0<z<4.5 observed with Chandra, utilizing over 1.6 Ms of total observing time, focusing on the rest-frame iron K emission from these sources. Although the X-ray signal-to-noise (S/N) currently available does not permit the detection of iron emission from the inner accretion disk in individual cases in our sample, we find significant structure in the stacked residuals. In addition to the narrow core, seen almost ubiquitously in local AGN, we find evidence for an additional underlying broad component from the inner accretion disk, with a clear red wing to the emission profile. Based on simulations, we find the detection of this broader component to be significant at greater than the 3-sigma level. This implies that iron emission from the inner disk is relatively common in the population of lensed quasars, and in turn further demonstrates that, with additional observations, this population represents an opportunity to significantly extend the sample of AGN spin measurements out to high-redshift.