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 .