A quasar under a microlensing caustic

Using observations of the high magnification event seen in image C of quasar Q2237+0305 during 1999 we have obtained constraints on the structure of the quasar’s central engine. Data taken with the Apache Point Observatory 3.5 mts telescope in the g’ and the r’ bands shows a smaller amplitude of the event in the r’ filter. We compare these observations and those presented by the OGLE team with synthetic source plane microlensing magnification patterns in order to obtain constraints on the size of the accretion disk regions contributing to each band. We obtain for the Gaussian width 1.20 × 10¹⁵M/0.1M cm σ_g 7.96 × 10¹⁵M/0.1M cm, where M is the mean microlensing mass, and a ratio σ_r /σ_g = 1.25⁺ ₋ ⁰ ₀ ⁴⁵ ₁₅. With the limits on the velocity of the lensing galaxy from Gil-Merino et al. (2005)[2] as our only prior, we obtain 0.60 × 10¹⁵M/0.1M cm σ_g 1.57 × 10¹⁵M/0.1M cm and a ratio σ_r /σ_g = 1.45⁺ ₋ ⁰ ₀ ⁹⁰ ₂₅ (all values at 68 percent confidence). Additionally, from our microlensing simulations we find that, during the chromatic microlensing event observed, the continuum emitting region of the quasar crossed a caustic at ≥ 72 percent confidence. This contribution is based on the research presented in Anguita et al. (2008)[1].