2004/08/31 by Michael J. Mortonson, Paul L. Schechter, J. Wambsganß +1 · 6 citations
Physics and Astronomy · #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/431195
published as Astrophys.J. 628 (2005) 594-603 · 27 pages, 11 figures; accepted for publication in ApJ; added section 4.3, Physical Values for Typical Quasars
arxiv created 2005/06/14 · openalex publication_date 2005/07/28 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
We examine the effect that the shape of the source brightness profile has on the magnitude fluctuations of images in quasar lens systems due to microlensing. We do this by convolving a variety of accretion disk models (including Gaussian disks, uniform disks, "cones," and a Shakura-Sunyaev thermal model) with two magnification maps in the source plane, one with convergence κ = 0.4 and shear γ = 0.4 (positive parity) and the other with κ = γ = 0.6 (negative parity). By looking at magnification histograms of the convolutions and using χ 2 tests to determine the number of observations that would be necessary to distinguish histograms associated with different disk models, we find that, for circular disk models, the microlensing fluctuations are relatively insensitive to all properties of the models except the half-light radius of the disk. Shakura-Sunyaev models are sufficiently well constrained by observed quasar properties that we can estimate the half-light radius at optical wavelengths for a typical quasar. If Shakura-Sunyaev models are appropriate, the half-light radii are very much smaller than the Einstein rings of intervening stars, and the quasar can be reasonably taken to be a point source except in the immediate vicinity of caustic-crossing events.