Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...424l..69p&link_type=abstract
Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 424, no. 2, p. L69-L72
Astronomy and Astrophysics
Astronomy
24
Data Reduction, Gravitational Lenses, Light (Visible Radiation), Molecular Clouds, Radio Astronomy, Radio Sources (Astronomy), Radio Spectra, Spiral Galaxies, Hubble Space Telescope, Image Processing, Red Shift, Sensitivity, Time Measurement, Very Large Array (Vla), Very Long Base Interferometry, Very Long Baseline Array (Vlba), Wavelengths
Scientific paper
We report the results of three high dynamic range, high-resolution radio observations with the Very Large Array (VLA), US Very Long Base Interferometry (VLBI) Network, and partially completed Very Long Baseline Array (VLBA) on the peculiar BL Lacertae objects PKS 1413+135. The VLA observations (resolution approximately 1.5 sec) reveal that PKS 1413+135 has no kiloparsec-scale extended structure to a dynamic range limit of 10,000:1. However, 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 structure among BL Lac objects but similar to a recently discovered class of VLBI 'mini-triples.' The presence of a counterjet at fluxes comparable to the main jet is incompatible with the standard relativistically beamed jet model for BL Lac objects and with the high value of core dominance exhibited by this source at arcsec resolution. This suggests a nonstandard interpretation in which the radio source lies far in the background of the spiral galaxy it is projected upon so that its VLBI structure may be affected by gravitational lensing. At 18 cm, the core is much weaker than at 3.6 cm suggesting free-free absorption by the high-column-density gas found along this sightline by previous infrared(IR)/optical, X-ray and redshifted H I 21 cm observations. We discuss the roles that free-free absorption and gravitational lensing may have for PKS 1413+135 and other GHz-peaked spectrum radio sources.
Carilli Chris L.
Ma Chopo
Perlman Eric Steven
Shaffer David B.
Stocke John T.
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