SIZE of the ACCRETION DISK in the GRAVIATIONALLY LENSED QUASAR SDSS J1004+4112 from the STATISTICS of MICROLENSING MAGNIFICATIONS

We present eight monitoring seasons of the four brightest images of the gravitational lens SDSS J1004+4112 observed between 2003 December and 2010 October. 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 λ_rest = 2407 Å) for the accretion disk using two different methods, = R_1/2 = 8.7^+18.5 _-5.5 √M/0.3M⊙ (histogram product) and = R_1/2 = 4.2^+3.2 _2.2 M/0.3M_⊙ lt-days (x²). The results are in agreement within uncertainties with the size predicted from the black hole mass in SDSS J1004 +4112 using thin disk theory.