X-Ray Observations of NGC 5128 (centaurus a) from UHURU

Observations have shown that the galaxy NGC 5128 located at the center of the radio source Cen A is the dominant source of X-ray emission from this region. We have further refined the source location box and have established a 2 a upper limit of 15' on the angular size of the X-ray source. The X-ray spectrum is substantially cut off with a low-energy exponential cutoff of 3.4 + 0.4 keV, corresponding to (9 j 3) x 1022 hydrogen atoms per cm2 along the line of sight. A flat power-law spectrum of energy index -0.7 1 0.3 is fitted to the data. The spectrum is very similar to that obtained for the source at the center of our Galaxy, suggesting an identification of the X-ray source with the core of NGC 5128. The low-energy X-ray cutoff coupled with radio observations from the inner lobes implies that the X-ray emission cannot come from the inner radio lobes. The X-ray absorption may be explained in terms of absorption of a source located in the central parts of the galaxy by the gas in the main part of the galaxy along the line of sight to the nucleus or by gas located in the nucleus of the galaxy. If the absorbing matter is in the nucleus of the galaxy, then a self-consistent model can be constructed. The radio emission comes from synchrotron radiation, the infrared emission from a surrounding cloud of dust and gas which absorbs the low frequency radio emission, and the X-ray emission from inverse Compton scattering of the infrared radiation by the synchrotron electrons. A 2 a upper limit from 1 to 10 keV of 0.05 keV cm 2 1 is determined for the extended radio lobes of Cen A. For a universal background temperature of 2.7 K we establish a lower limit of 0.6 microgauss on the magnetic field of the extended radio lobes. Subject headings: galactic nuclei - galaxies, individual - magnetic fields - X-ray sources