I was thinking that the arced lensed images of distant galaxies around galaxy clusters, such as Abell 370 might not be because of their huge mass but be caused by reflections through gas shells surronding these clusters. This would be similar to the way an xray telescope works, by grazing incidence. Arp writes about shells of gas around galaxies and clusters, and since BL Lac's are embedded in gas and dust
and become galaxy clusters this would seem to fit much better. It would be interesting to see how a gavitational lens and a gas grazing incidence reflection would compare at different frequencies, such as radio, infared and light rays, there should be some obvious differences.

*nod* As far as I know, a gravitational lens would affect all frequencies equally, but yes, a reflection or refraction would have some significant differences by frequency.

I can't find anything on multiple frequencies, though. The image was composed of green, red and infrared - those line up. I haven't found anything more recent radio-wise than the old SCUBA attempts - that's too low a resolution.

I did find some radio arces on the Merlin/VLBI site, but no optical conterpart. I read someplace that a gravitational lens should be acromatic, but will it bend electromagnetic waves the same amount across the whole spectrum? If that is so, then radio freqs should show the same arc if the source is radiating across the spectrum. You would think with the subarc resolution of the VLBI that they have a pretty picture of gravitational arcs at radio and optical freqs, like the one of Centaurus A, showing its radio and xray jets!