Intrinsic intraday variability in the gravitational lens system   B0218+357
  Radio monitoring of the gravitational lens system B0218+357 reveals it to be a highly variable source with variations on timescales of a few days correlated in both images. This shows that the variability is intrinsic to the background lensed source and suggests that similar variations in other intraday variable sources can also be intrinsic in origin. 
A. D. Biggs, I. W. A. Browne, P. N. Wilkinson (University of   Manchester, JBO)