Quantitative Interpretation of Quasar Microlensing Light Curves
Abstract
We develop a general method for analyzing the light curves of microlensed quasars and apply it to the OGLE light curves of the fourimage lens Q2237+0305. We simultaneously estimate the effective source velocity, the average stellar mass, the stellar mass function, and the size and structure of the quasar accretion disk. The light curves imply an effective sourceplane velocity of 10,200kms^{1}<~v_{e}h<M/M_{solar}>^{1/2}<~39,600 km s^{1} (68% confidence). Given an independent estimate for the source velocity, found by combining estimates for the peculiar velocity of the lens galaxy with its measured stellar velocity dispersion, we obtain a mean stellar mass of <M>~=0.037 h^{2} M_{solar} (0.0059h^{2}M_{solar}<~<M><~0.20h^{2}M_{solar}). We were unable to distinguish a Salpeter mass function from one in which all stars had the same mass, but we do find a strong lower bound of κ_{*}/κ>~0.5 on the fraction of the surface mass density represented by the microlenses. Our models favor a standard thin accretion disk model as the source structure over a simple Gaussian source. For a faceon, thin disk radiating as a blackbody with temperature profile T_{s}~R^{3/4}, the radius r_{s} where the temperature matches the filter pass band [2000 Å or T_{s}(r_{s})~=7×10^{4} K] is 1.4×10^{15}h^{1}cm<~r_{s}<~4.5×10^{15}h^{1}cm. The flux predicted by the disk model agrees with the observed flux of the quasar, so nonthermal or optically thin emission processes are not required. From the disk structure we estimate a black hole mass of M_{BH}~=1.1^{+1.4}_{0.7}×10^{9}h^{3/2}η^{1/2}_{0.1}(L/L_{E})^{1/2}M_{solar}, consistent with the mass estimated under the assumption that the quasar is radiating at the Eddington luminosity (L/L_{E}=1).
 Publication:

The Astrophysical Journal
 Pub Date:
 April 2004
 DOI:
 10.1086/382180
 arXiv:
 arXiv:astroph/0307422
 Bibcode:
 2004ApJ...605...58K
 Keywords:

 Accretion;
 Accretion Disks;
 Cosmology: Dark Matter;
 Cosmology: Gravitational Lensing;
 Galaxies: Quasars: Individual: Alphanumeric: Q2237+0305;
 Stars: Luminosity Function;
 Mass Function;
 Astrophysics
 EPrint:
 39 pages, 11 figures (some only in jpeg format), submitted to ApJ