More rambles on cosmic string lenses
This quasar has a well studied time delay, used to get an independent estimate of Hubble's constant, H0. or equivalently, the expansion rate of the universe. Analysis shows a second time scale for the time delay between the two images, which has been suggested is due to microlensing in the lensing galaxy. The new claim is for a third time scale, at low amplitude variability, with zero time delay offset - consistent with string lensing.
Sorry, but I don't believe it. The model parameters are implausible (if I read it correctly they require the lensing string be in the Milky Way, only 10,000 light years away), and the alignment with a classic lens is a priori very unlikely. Likely there's some instrumental systematic here, problem with baseline photometry.
Back to CSL-1: quick glance at the spectrum does not show any obvious AGN emission lines, so maybe x-ray observation is not a good bet - though if there were identical luminosity x-ray emitting nuclei in both images, it would strengthen the case, and there could be room for a low luminosity AGN, but one still detectable with Chandra. Similarly radio observation looking for low frequency radio emission would be a test, if both images had identical emission.
astro-ph/0406516, but Sazhin et al, discusses the statistics of close pairs of faint extended sources in the field, and the possibility of multiple other lenses along the string trajectory - they claim 11 source pairs (7-9 expected for a straight string, more for a curved string, so implication is a lightly curved string). Too early to tell if these are real, of course, but if they are, they've not only found a string but mapped it...
Still a long shot, but not crazy. Certainly worth some followup.