X-ray microlensing in the quadruply lensed quasar Q2237+0305

TL;DR

This study analyzes X-ray data of the quadruply lensed quasar Q2237+0305, revealing microlensing effects and indicating that the X-ray emission region is smaller than the optical one, using archival Chandra observations.

Contribution

First detection of X-ray microlensing in Q2237+0305, demonstrating the smaller size of the X-ray emission region compared to optical based on flux ratio variations.

Findings

Detected strong flux variations up to a factor of 4 within a month.

Found evidence for microlensing in image A through flux ratio analysis.

X-ray flux ratio variations are larger than optical, indicating a smaller X-ray emission region.

Abstract

We use archival data of NASA's Chandra X-ray telescope to compile an X-ray light curve of all four images of the quadruply lensed quasar Q2237+0305 (z=1.695) from January 2006 to January 2007. We fit simulated point spread functions to the four individual quasar images using Cash's C-statistic to account for the Poisson nature of the X-ray signal. The quasar images display strong flux variations up to a factor of ~4 within one month. We can disentangle the intrinsic quasar variability from flux variations due to gravitational microlensing by looking at the flux ratios of the individual quasar images. Doing this, we find evidence for microlensing in image A. In particular, the time-sequence of the flux ratio A/B in the X-ray regime correlates with the corresponding sequence in the optical monitoring by OGLE in the V-band. The amplitudes in the X-ray light curve are larger. For the most prominent peak, the increase of the X-ray ratio A/B is larger by a factor ~1.6 compared to the signal in the optical. In agreement with theory and other observations of multiply imaged quasars, this suggests that the X-ray emission region of this quasar is significantly smaller than the optical emission region.