EVN observations of the lens system B0128+437

Abstract

Previous VLBI observations of the lens system CLASS B0128+437 showed that the lensed source had a triple sub-component structure. However, one of the images looked very different to the others and it has been suggested that this is due to scatter-broadening in the ISM of the lensing galaxy. We present a new 21-cm EVN map of this system, the low frequency compared to previous epochs chosen as the scattering should be more pronounced at this frequency. Analysis of the new map is at an early stage, but the area of scattering in the affected image is extremely obvious. Other points of interest that we seek to explain are the very large sizes of the images (in conflict with the observed spectral turnover at about 1 GHz) and the different position angle of one of the images at different frequencies.