J. M. Benson

Radio morphology of 3C 120 on scales from 0. 5 parsecs to 400 kiloparsecs

VLA observations of the radio source 3C 120 on scales from 0.1 arcsec to over 14 arcmin were made, and the resulting maps are presented and discussed. The radio emission shows structure on all scales from less than a pc to greater than 400 kpc. A continuously connected jet is visible from less than a parsec from the central engine to over 100 kpc, well outside the galaxy. There is a lobe in the counterjet direction and diffuse emission in several directions. The three-dimensional morphology is not clear but might resemble some of the large double or wide-angle head-tail sources seen along the axis of the jet. The polarization observations imply a longitudinal magnetic field throughout nearly all of the jet. The brightness of the jet decreases following a simple power law with width, implying that the physical parameters also follow simple power laws. These results are interpreted in the context of the incoherent synchrotron model for radio emission. 60 references.

PROGRESS IN MEASUREMENTS OF THE GRAVITATIONAL BENDING OF RADIO WAVES USING THE VLBA

We have used the Very Long Baseline Array (VLBA) at 43, 23, and 15 GHz to measure the solar gravitational deflection of radio waves among four radio sources during an 18 day period in 2005 October. Using phase-referenced radio interferometry to fit the measured phase delay to the propagation equation of the parameterized post-Newtonian formalism, we have determined the deflection parameter γ = 0.9998 ± 0.0003 (68% confidence level), in agreement with general relativity. The results come mainly from 43 GHz observations where the refraction effects of the solar corona were negligible beyond 3 deg from the Sun. The purpose of this experiment is three-fold: to improve on the previous results in the gravitational bending experiments near the solar limb; to examine and evaluate the accuracy limits of terrestrial VLBI techniques; and to determine the prospects and outcomes of future experiments. Our conclusion is that a series of improved designed experiments with the VLBA could increase the presented accuracy by at least a factor of 4.

Parallax and Kinematics of PSR B0919+06 from VLBA Astrometry and Interstellar Scintillometry

Results are presented from a long-term astrometry program on PSR B0919+06 using the NRAO Very Long Baseline Array. With 10 observations (seven epochs) between 1994 and 2000, we measure a proper motion μα = 18.35 ± 0.06 mas yr-1, μδ = 86.56 ± 0.12 mas yr-1 and a parallax π = 0.83 ± 0.13 mas (68% confidence intervals). This yields a pulsar distance of 1.21 ± 0.19 kpc, making PSR B0919+06 the farthest pulsar for which a trigonometric parallax has been obtained, and the implied pulsar transverse speed is 505 ± 80 km s-1. Combining the distance estimate with interstellar scintillation data spanning 20 yr, we infer the existence of a patchy or clumpy scattering screen along the line of sight in addition to the distributed electron density predicted by models for the Galaxy and constrain the location of this scattering region to within ~250 pc of the Sun. Comparison with the lines of sight toward other pulsars in the same quadrant of the Galaxy permits refinement of our knowledge of the local interstellar medium in this direction.

VLBI and Merlin observations of 3C 120 at 1. 7 GHz - superluminal motions beyond 0. 05 arcsec

The radio galaxy 3C 120 was observed at 1.7 GHz in 1982 and 1984 with VLBI arrays, and the results are reported. Significant changes in the radio structure are seen on scales out to 100 mas between two observations separated by 1.5 yr. The changes indicate the presence of superluminal motions at 50 mas and probably at 90 mas from the core. These are the largest angular scales on which superluminal motions have been observed. The continuity of the 3C 120 jet on scales of a fraction of an arcsec is established. The observations that the jet does not slow down over an order of magnitude in core distance, combined with the continuity of the physical parameters deduced from observations over many orders of magnitude in core distance, suggests that the jet remains relativistic on even larger scales. This supports the concept that the powerful, one-sided jets are relativistic on all scales and that the one-sidedness is the result of relativistic beaming. 31 references.

Probing the Accretion Region of NGC 1275 with VLBI

Multi-frequency VLBA observations were used to study the magnitude and radial dependence of free-free absorption of the radio emission from the counterjet in 3C 84.