Two Close-Separation Quasar-Quasar Pairs in the Large Bright Quasar Survey

Abstract

We present photometric and spectroscopic observations of two close quasar-quasar pairs found in the Large Bright Quasar Survey (LBQS) (Hewett et al. 1995, AJ, 109, 1498). The two components of the 2153-2056 pair ($z=1.845$, $\Delta\theta=7\farcs8$, $B=17.9$ and 21.3) have the same redshifts within the relatively large uncertainty, $\Delta v_{A-B} =-1100\pm1500 km s^{-1}$, of the observations. The quasars are most likely spatially coincident although the possibility that the pair is the result of gravitational lensing cannot be ruled out. The two components of 1148+0055 ($z=1.879$, $B=18.5$ and $z=1.409$, $B=21.1$, $\Delta\theta=3\farcs9$) have disjoint redshifts and the pair has attracted some attention in the context of gravitational lensing (e.g. Wampler 1997, ApJ, 476, L55) following the independent discovery of the pair by Surdej and collaborators. Four close, $\Delta\theta \le10\farcs0$, quasar-quasar pairs have now been discovered in the LBQS and we discuss the probability of identifying pairs with disjoint redshifts and of locating spatially coincident pairs from the systematic investigation of the well-defined quasar catalogue.