Spectral Evolution in Young Active Galactic Nuclei
The spectral evolution of AGNs is discussed within the context of a scenario where the cosmic X-ray background (CXB) is dominated by these sources. Attention is drawn to the fact that individually observed AGN X-ray spectra are significantly steeper than that of the CXB. The remarkably flat spectrum thereby required for the “as-yet” unresolved sources of the residual CXB is interpreted as an observational constraint on an earlier stage of AGN evolution. Assuming black hole disk accretion, a picture emerges where young AGNs are compact Eddington limited thermal X-ray sources and where canonical AGNs represent later stages in which they have become appreciably less compact, exhibiting the importance of non-thermal disk-dynamo processes.
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- Bardeen, J. 1972, in Black Holes, ed. C. DeWitt and B.S. DeWitt (New York: Gordon & Breach), p. 225.Google Scholar
- Cavallo, G., and Rees, M. 1978, M.N.R.A.S., 183, 43.Google Scholar
- Elvis, M. 1985, Proc. U.S./Japan Symp. (Jan. 1985); in press. CFA Preprint #2126.Google Scholar
- Elvis, M., Wilkes, B., and Tananbaum, H. 1985, Ap. J., 292, in press.Google Scholar
- Zdziarski, A., and Lightman, A. 1984, Ap. J. (Letters), submitted.Google Scholar