Size of the accretion disk in the gravitationally lensed quasar SDSS J1004+4112 from the statistics of microlensing magnifications

TL;DR

This study uses microlensing magnification statistics from multi-year observations of a gravitationally lensed quasar to estimate the size of its accretion disk, finding results consistent with thin disk theory predictions.

Contribution

It provides the first size estimate of the quasar's accretion disk using microlensing data, employing two different statistical methods for validation.

Findings

Estimated accretion disk size: approximately 4.2 to 8.7 light-days.

Results agree with theoretical predictions from thin disk models.

Microlensing amplitude variations reveal disk structure at rest wavelength 2407 Å.

Abstract

We present eight monitoring seasons of the four brightest images of the gravitational lens SDSS J1004+4112 observed between December 2003 and October 2010. Using measured time delays for the images A, B and C and the model predicted time delay for image D we have removed the intrinsic quasar variability, finding microlensing events of about 0.5 and 0.7 mag of amplitude in the images C and D. From the statistics of microlensing amplitudes in images A, C, and D, we have inferred the half-light radius (at {\lambda} rest = 2407 {\AA}) for the accretion disk using two different methods, $R_{1/2}=8.7^{+18.5}_{-5.5} \sqrt{M/0.3 M_\odot}$ (histograms product) and $R_{1/2} = 4.2^{+3.2}_{-2.2} \sqrt{M/0.3 M_\odot}$ light-days ($\chi^2$). The results are in agreement within uncertainties with the size predicted from the black hole mass in SDSS J1004+4112 using the thin disk theory.