2006ApJ...636L...5S

CSL 1 is a peculiar object (R.A.=12^h23^m30{fs}5, decl.=-12°38'57".0 [J2000.0]) that, because of its photometric and spectroscopic properties, is possibly the first case of gravitational lensing by a cosmic string. In this Letter we present additional evidence, based on medium to high resolution VLT+FORS1 observations, that the spectra of the two components of CSL 1 are identical within a confidence level higher than 98% and that the velocity difference of the two components is consistent with zero. This result adds further confidence to the interpretation of the system as a true lens.