Nine lensed quasars and quasar pairs discovered through spatially extended variability in Pan-STARRS

Frédéric Dux, Cameron Lemon, Frédéric Courbin, Favio Neira, Timo Anguita, Aymeric Galan, Sam Kim, Maren Hempel, Angela Hempel, Régis Lachaume

Research output: Contribution to journalArticlepeer-review


We present the proof of concept of a method for finding strongly lensed quasars using their spatially extended photometric variability through difference imaging in cadenced imaging survey data. We applied the method to Pan-STARRS, starting with an initial selection of 14 107 Gaia multiplets with quasar-like infrared colours from WISE. We identified 229 candidates showing notable spatially extended variability during the Pan-STARRS survey period. These include 20 known lenses and an additional 12 promising candidates for which we obtained long-slit spectroscopy follow-up. This process resulted in the confirmation of four doubly lensed quasars, four unclassified quasar pairs, and one projected quasar pair. Only three are pairs of stars or quasar+star projections. The false-positive rate accordingly is 25%. The lens separations are between 0.81′ and 1.24′, and the source redshifts lie between z = 1.47 and z = 2.46. Three of the unclassified quasar pairs are promising dual-quasar candidates with separations ranging from 6.6 to 9.3 kpc. We expect that this technique is a particularly efficient way to select lensed variables in the upcoming Rubin-LSST, which will be crucial given the expected limitations for spectroscopic follow-up.

Original languageEnglish
Article numberA47
JournalAstronomy and Astrophysics
Publication statusPublished - 1 Feb 2024


  • Gravitation
  • Gravitational lensing: strong
  • Quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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