The double quasar 1548+115a,b as a gravitational lens

The two quasars 1548+ liSa (17th mag; z = 0.4359) and 1548+115b (19th mag; I = 1.901) are separated by only 5 of arc. We consider the possibility that the light from the distant quasar is enhanced by the gravitational-lens effect of the nearby quasar and any galaxy in which it may reside. The observed separation allows one immediately to set a strict upper limit of 7 >c 10i on the mass of the system containing 1548a. If ) is between about 4 and 7 X 1012 , gravitational-lens brightening of 1548b roughly doubles our probability of finding such a close pair. It is perhaps significant that this mass range is lust that observed for giant elliptical galaxies (radio galaxies). It is likely that the lens forms a fainter but still observable secondary image of 1548b on the other side of 1548a. Identification of such a secondary image would verify the lens effect and indicate that the two quasars are seen in projection rather than being physically connected. Subject headings: gravitation - quasi-stellar sources or objects