On the physical environment in galactic nuclei

Galactic nuclei quasars emit radiation over the entire electromagnetic spectrum. There is considerable interest in the nature of the emission mechanisms which may be responsible for the observed radiation. The possiblity that a single mechanism is responsible for a wide frequency range of the electromagnetic flux suggests that multiple frequency observations of galactic nuclei and quasars can be used to place constraints on models for the source mechanisms involved. In conjunction with observations by the High Energy X-ray Spectrometer on OSO-8, four extragalactic sources have been investigated in this manner: (1) the nucleus of the elliptical galaxy, Centaurus A (NGC 5128); (2) the quasar, 3C273; (3) the nucleus of the Seyfert galaxy, NGC 4151; and (4) the nucleus of the Milky Way galaxy. Concurrent observations have been taken for Cen A at radio and X-ray frequencies, and for NGC 4151 at radio, infrared, optical, and X-ray frequencies. The data from these observations and from other work are used to construct composite spectra (radio to gamma-ray) for the sources. Additionally, a computer program has been developed to obtain source strengths from regions of the sky where more than one source is in the OSO-8.