Speaker
Description
The flux magnification by strong gravitational lensing allows detailed observations of QSOs at high redshifts which would otherwise only be possible for a few extremly luminous objects. Recently there has also been renewed interest in the study of lensed QSOs due to the possibility of independent and accurate measurements of the Hubble constant using time-delay cosmography in lensed QSO systems. We have been using X-ray sources from the eRASS1 catalogue in combination with Gaia measurements to identify new lensed QSO candidates. We have so far spectroscopically confirmed 4 new QSO lenses and 14 physical pairs of AGN. For the brightest of the new systems, eRASS1 J050129.5-073309, we were able to measure a time delay of ~100 days between the light curves of the 2 lensed components. Due to its brightness (among the 10 X-ray brightest QSO lenses in the eRASS1 survey) and its potential use for time-delay cosmography we have initiated follow-up observations of this object with Chandra, XMM-Newton and HST.
