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