Discovery of Energy Dependent X-ray Microlensing in Q2237+0305

TL;DR

This study presents a decade of Chandra X-ray observations of quasar Q2237+0305, revealing energy-dependent microlensing effects that suggest a non-uniform corona structure around the black hole.

Contribution

First detection of chromatic X-ray microlensing differences, indicating energy-dependent source sizes and electron distributions in the quasar's corona.

Findings

Hard X-ray band is more strongly microlensed than soft band.

X-ray emission regions are more compact than optical regions.

Chromatic microlensing differences suggest non-uniform electron distribution in the corona.

Abstract

We present our long term Chandra X-ray monitoring data for the gravitationally lensed quasar Q2237+0305 with 20 epochs spanning 10 years. We easily detect microlensing variability between the images in the full (0.2--8 keV), soft (0.2--2 keV), and hard (2--8 keV) bands at very high confidence. We also detect, for the first time, chromatic microlensing differences between the soft and hard X-ray bands. The hard X-ray band is more strongly microlensed than the soft band, suggesting that the corona above the accretion disk thought to generate the X-rays has a non-uniform electron distribution, in which the hotter and more energetic electrons occupy more compact regions surrounding the black holes. Both the hard and soft X-ray bands are more strongly microlensed than the optical (restframe UV) emission, indicating that the X-ray emission is more compact than the optical, confirming the microlensing results from other lenses.