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Session 117 - Instrumentation and Techniques.
Oral session, Thursday, January 18
Salon del Rey North, Hilton

[117.05] New Gravitational Lens Candidates from VLA snapshots of MG and PMN radio sources

A. Fletcher, S. Conner, A. Cooray, B. Burke (MIT), L. Herold (CIW and MIT)

The four 4.85 GHz MIT-Greenbank (MG) surveys together revealed 20,344 radio sources over 5.0 steradians (-0.\deg5<\delta<51\deg;|b|>10\deg), down to a limiting flux density of S_4.85\sim41 mJy. The 4.85 GHz Parkes-MIT-NRAO (PMN) Southern survey lists 23,277 sources over 2.5 steradians (-87.\deg5<\delta<-37\deg;|b|>10\deg), down to S_4.85\sim35 mJy, while the Tropical and Equatorial surveys (-29\deg<\delta<+10\deg;|b|>10\deg) together give 25,137 sources over 3.9 steradians, down to S_4.85\sim40 mJy. The estimated completeness for each of these surveys is >93%, while their reliabilities are >90%. Over the past 15 years, the MIT group has been imaging flux-limited samples of these sources with the VLA, at 4.85 and 8.43 GHz. One of our goals is to find new instances of gravitational lensing, and another is to systematically study the radio and optical properties of radio-loud AGN. We now have VLA snapshots of \sim 6500 MG and \sim 2000 PMN sources. The initial 1980's 4.85 GHz imaging attempt on MG sources found 5 bona fide lenses: MG 2016 (triple), MG 1131 (ring), MG 0414 (quad), MG 1654 (ring), MG 1549 (ring). From the 1990's 8.43 GHz effort, we present 5 new examples of gravitational lens candidates: MG 0248 (ring?), MG 1011 (triple?), PMN 1254 (quad?), PMN 1542 (quad?) and PMN 0837 (ring?). We have also found \sim 120 ``close'' double-lobed radio galaxies (0.''25<\theta<2''), whose physical nature is not yet understood - perhaps some of these may be doubly-imaged lenses. Our deep CCD imaging campaign, using the Michigan-Dartmouth-MIT telescopes, has identified optical counterparts (17 Program listing for Thursday