Discovering Gravitational Lenses through Measurements of Their Time Delays

We consider the possibility that future wide-field time-domain opticalimaging surveys may be able to discover gravitationally lensed quasar pairsthrough serendipitous measurements of their time delays. We discuss the meritssuch a discovery technique would have relative to conventional lens searches.Using simulated quasar lightcurves, we demonstrate that in a survey whichobserves objects several times each lunar cycle over the course of five years,it is possible to improve the efficiency of a gravitational lens search by 2-3orders of magnitude through the use of time delay selection. In the mostadvantageous scenario considered, we are able to improve efficiency by a factorof 1000 with no loss of completeness. In the least advantageous scenario, weare able to improve efficiency by a factor of 110 while reducing completenessby a factor of 9. We show that window function effects associated with thelength of the observing season are more important than the total number ofdatapoints in determining the effectiveness of this method. We alsoqualitatively discuss several complications which might be relevant to a realtime delay search.Comment: 22 pages, 7 figures. Submitted to Ap