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New light curves of the gravitationally lensed double quasar Q0957+561 in thegr bands during 2008-2010 include densely sampled, sharp intrinsic fluctuationswith unprecedentedly high signal-to-noise ratio. These relatively violent fluxvariations allow us to very accurately measure the g-band and r-band timedelays between the two quasar images A and B. Using correlation functions, weobtain that the two time delays are inconsistent with each other at the 2sigmalevel, with the r-band delay exceeding the 417-day delay in the g band by about3 days. We also studied the long-term evolution of the delay-corrected fluxratio B/A from our homogeneous two-band monitoring with the Liverpool RoboticTelescope between 2005 and 2010. This ratio B/A slightly increases in periodsof violent activity, which seems to be correlated with the flux level in theseperiods. The presence of the previously reported dense cloud within the cDlensing galaxy, along the line of sight to the A image, could account for theobserved time delay and flux ratio anomalies.

A 5.5-year robotic optical monitoring of Q0957+561: substructure in a non-local cD galaxy