HIGH DYNAMIC-RANGE RADIO OBSERVATIONS OF PKS-1413- A BL LACERTAE OBJECT WITH A PARSEC-SCALE COUNTERJET(135 )

We report the results of three high dynamic range, high-resolution rad io observations with the VLA, US VLBI Network, and partially completed VLBA on the peculiar BL Lacertae objects PKS 1413 + 135. The VLA obse rvations (resolution - 1.5'') reveal that PKS 1413 + 135 has no kilopa rsec-scale extended structure to a dynamic range limit of 10,000:1. Ho wever, its milliarcsecond-scale structure appears to be a triple (i.e. , a core, jet plus '' counterjet '') at both 3.6 and 18 cm, a unique s tructure among BL Lac objects but similar to a recently discovered cla ss of VLBI ''mini-triples.'' The presence of a counterjet at fluxes co mparable to the main jet is incompatible with the standard relativisti cally beamed jet model for BL Lac objects and with the high value of c ore dominance exhibited by this source at arcsec resolution. This sugg ests a nonstandard interpretation in which the radio source lies far i n the background of the spiral galaxy it is projected upon so that its VLBI structure may be affected by gravitational lensing. At 18 cm, th e core is much weaker than at 3.6 cm suggesting free-free absorption b y the high-column-density gas found along this sightline by previous I R/optical, X-ray and redshifted H I 21 cm observations. We discuss the roles that free-free absorption and gravitational lensing may have fo r PKS 1413 + 135 and other GHz-peaked spectrum radio sources.