X-Ray Imaging Observations of the Radio Galaxies CEN a, VIR a, and 3C273.

This dissertation reports results from detailed two-dimensional X-ray images of three radio galaxies obtained with the High Resolution Imager and Imaging Proportional Counter on board the Einstein X-ray Observatory (HEAO-B satellite). The images reveal several distinct sources of X-ray emission in these galaxies including the active nucleus, hot interstellar medium, stars, radio lobes and jets. The most important result is the discovery of X -ray jets in all three of these galaxies, demonstrating that highly energetic processes occur in the transport of energy and matter from radio galaxy nuclei to lobes. In addition, we provide the strongest evidence to date for inverse Compton X-ray emission from extended radio lobes, and for hydrostatic (in contrast to ram) pressure confinement of radio lobes by a hot external medium. In Centaurus A = NGC 5128, the most dramatic X -ray structure is a linear jet of emission extending 8'' to 4' (0.2 to 6 kpc) from the nucleus towards the NE radio lobes. It consists of several resolved knots about 150 pc in radius, each emitting 10('38) - 10('39) erg/s in soft X-rays. Various thermal and non-thermal models for the emission are considered in detail; none can be rigorously excluded with the available evidence. Also present in the images of Cen A are: X-ray emission associated with the outer optical jet and radio lobe; a ridge of emission below and parallel to the dust lane, probably produced by Population I sources; diffuse emission absorbed along the dust lane, probably due to a hot interstellar medium of about 10('8) M(,(CIRCLE)); the strong, variable nuclear source; and five X-ray sources unrelated to the galaxy, including a probable distant RS CVn binary system. The diffuse component provides one of the few indications of an interstellar medium in an isolated elliptical galaxy. X-ray emission from the radio galaxy Vir A = M87 = 3C274 is dominated by the dense gaseous medium in the galaxy, but emission from the radio/optical synchrotron jet (12'' from the nucleus), the radio halo (1' to 3'), and the nucleus itself are also seen. The jet intensity, corresponding to 10('41) erg/s in soft X-rays, lies near an extrapolation of its optical spectrum. This, along with inadequacies of inverse Compton and thermal models, indicates that the X-ray production mechanism is also synchrotron. In situ reacceleration of electrons up to 10('13) eV is required in the jet. The detection of diffuse emission from the misaligned outer lobes constituting the radio halo is fully consistent with the presence of inverse Compton X-ray emission. The interstellar medium is sufficiently dense to confine the inner and outer radio lobes (though not the jet) by hydrostatic pressure; ram pressure is not required. A fairly weak compact X-ray source is found at the nucleus of the galaxy, and a serendipitous source is found with no optical counterpart brighter than 23.5('m). The nearby quasar 3C273 was imaged at high resolution, and a very faint excess of counts is found at the location of the radio/optical jet 10'' to 20'' SW of the nucleus. The jet X-ray emission, corresponding to about 10('43) erg/s, is consistent with the synchrotron model of the M87 jet scaled up a factor of 10('2) in size and luminosity. The nucleus emission varied in intensity by 10% in less than 12 hours during the observation. This indicates that the X-ray emission region is either highly inhomogeneous or physically distinct from the gamma-ray emitting region.