Microlensing induced spectral variability in Q2237+0305

TL;DR

This study provides direct evidence of microlensing affecting the spectral features of quasar Q2237+0305, revealing the relative sizes of its nuclear regions through spectroscopic variability analysis.

Contribution

First detection of microlensing-induced spectral variability in a quasar, constraining the size of the UV continuum and broad emission line regions.

Findings

UV continuum region < 0.05 pc in size

Spectroscopic differences due to microlensing

Emission line regions are larger than the continuum region

Abstract

We present both photometry and spectra of the individual images of the quadruple gravitational lens system Q2237+0305. Comparison of spectra obtained at two epochs, separated by $\sim~3\,$years, shows evidence for significant changes in the emission line to continuum ratio of the strong ultraviolet CIV~$\lambda$1549, CIII]~$\lambda$1909 and MgII~$\lambda$2798 lines. The short, $\sim~1\,$day, light--travel time differences between the sight lines to the four individual quasar images rule out any explanation based on intrinsic variability of the source. The spectroscopic differences thus represent direct detection of microlensing--induced spectroscopic differences in a quasar. The observations allow constraints to be placed on the relative spatial scales in the nucleus of the quasar, with the ultra--violet continuum arising in a region of $\la~0.05~{\rm pc}$ in extent, while the broad emission line material is distributed on scales much greater than this.