Contemporaneous X-Ray and VLBI Radio Observations of the Quasar NRAO 140

Abstract

The quasar NRAO 140 was observed at various times between 1978 and 1985 at X-ray energies using HEAO I, the Einstein Observatory, and EXOSAT. The author also observed this source a number of times with multifrequency VLBI between 1980 and 1984. In this paper, the author combines new observations with those previously published to present a time history of the X-ray emission and radio structure of NRAO 140 between 1978 and 1985. The new observations of the compact radio structure reveal a jet composed of seven components. The two components closest to the "core" are separating superluminally from the core. The 18, 6, 2.8, and 1.3 cm VLBI observations obtained in 1984 allow a detailed dissection of the spectrum into its various components. The X-ray photoelectric absorption cutoff moved to significantly higher energy in 1980 compared to 1979 and 1985. This corresponds to an increase in the column density of cold gas along the line of sight in 1980. The X-ray absorption in 1979 and 1985 is consistent with that expected from H I and H_2_ in our Galaxy. The X-ray flux declined by about a factor of 2 between 1979 and 1985, while the flux density of the compact radio core declined by a similar factor between 1980 and 1984. This coincidence, combined with the statistical correlations between compact radio and X-ray fluxes of quasars, suggests that there is a direct causal connection between the compact radio core and the X-ray emitting region.