A small source in Q2237 0305?

Abstract

Microlensing in Q2237+0305 between 1985 and 1995 has been interpreted in two different ways. First, the observed variations can be explained through microlensing by stellar mass objects of a continuum source with dimensions significantly smaller than the microlens Einstein Radius (η0), but consistent with that expected for thermal accretion discs. However, other studies have shown that models having sources as large as 5η0 can reproduce the observed variation. In this paper we present evidence in favour of a small source. Our approach uses the distribution of microlensed light-curve derivatives to place statistical limits (as a function of source size) on the number of microlens Einstein rad..