Abstract
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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Boldt, E., Leiter, D. (1986). Spectral Evolution in Young Active Galactic Nuclei. In: Giuricin, G., Mardirossian, F., Mezzetti, M., Ramella, M. (eds) Structure and Evolution of Active Galactic Nuclei. Astrophysics and Space Science Library, vol 121. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-4562-3_22
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DOI: https://doi.org/10.1007/978-94-009-4562-3_22
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