Milliarcsecond X-ray astrometry to resolve inner regions of AGN at $z>1$ using gravitational lensing

TL;DR

This paper introduces a novel milliarcsecond X-ray astrometry method for strongly lensed AGN at high redshift, enabling precise localization of X-ray sources and revealing potential offset AGN candidates, thus advancing supermassive black hole studies.

Contribution

The paper develops a new Bayesian lens modelling technique that achieves unprecedented X-ray astrometric precision for high-redshift AGN, surpassing existing instrument capabilities.

Findings

X-ray sources localized within 11 mas and 9 mas of radio sources.

X-ray and optical emissions are co-spatial in one AGN, offset in another.

Method enables detection of offset and binary AGN at $z>1$.

Abstract

We report the localization of the X-ray emission from two strongly lensed AGN, CLASS B0712+472 ($z=1.34$) and CLASS B1608+656 ($z=1.394$). We obtain milliarcsecond X-ray astrometry by developing a novel method that combines parametric lens modelling with a Bayesian analysis. We spatially locate the X-ray sources in CLASS B0712+472 and CLASS B1608+656 within 11 mas and 9 mas from the radio source, respectively. For CLASS B0712+472, we find that the X-ray emission is co-spatial with the radio and optical emission. While, in CLASS B1608+656, the X-ray emission is co-spatial with radio, but displaced with respect to the optical emission at 1$\sigma$ level, which positions this source as an offset AGN candidate. This high astrometric precision improves on the limitations of existing X-ray instruments by two orders of magnitude. The demonstrated method opens a path to search for offset and binary AGN at $z>1$, and to directly test supermassive black hole formation models in a redshift range that has been mostly underconstrained to date.