High-Energy Astrophysics American and Soviet Perspectives/Proceedings from the U.S.-U.S.S.R. Workshop on High-Energy Astrophysics (1991) / Chapter Skim
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X-RAY EMISSION FROM ACTIVE GALACTIC NUCLEI
X-RAY EMISSION FROM ACTIVE GALACTIC NUCLEI
Pages 297-306
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From page 297... ...
Men a powerlaw model is fit to the IPC data they find a correlation between X-ray spectral index and radio properties, with radio loud objects having an X-ray energy index ~ ~ 0.5 and radio quiet objects have cat ~ 1.0. Their data also show a broad distribution in X-ray specUal indices.
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From page 298... ...
As shown in Figure 1 many of these objects have a soft excess over a simple power law fit ~ the Exosat data. It thus seems that a simple power law model is not an adequate fit to the spectrum of Seyfert galaxies in the 0.2-4.0 kev band and that both Exosat and the Einstein IPC frequently "agree" as to which objects are steep at low energies.
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From page 299... ...
It is possible to fit more complex models man single power laws to the combined simultaneous Einstein solid state spectrometer (SSS) and monitor proportional counter (MPC)
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From page 300... ...
Preliminary results from the IPC+MPC fitting for 26 objects indicate that, for those objects for which the IPC data have been fit by single "steep" power laws that complex models are preferred systematically over single power laws. The indications are that an additional soft component is required for ~ 2/3 of the observations and this component is very soft for only ~ 1/3 of the these observations (e.g., ~ 10% of the total sample)
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From page 301... ...
BBXRrs great sensitivity to spectral lines will test whether any of the optically thin models for the formation of the soft component are "correct". The frequent presence of "soft excess" in the spectra of active galaxies implies that if they are a major contn~utor to the cosmic X-ray background that the spectral form of the background should change at E < 2 kev (Boldt 1987~.
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From page 302... ...
indicate that if an accretion disk or other source of "cold material" exists close to the central engine, as is required in almost any accretion model of AGN, that significant reprocessing can take place which should distort He 10-200 kev spectrum in a particular fashion depending on whether reflectance or transmission dominates. There are indications from Toga data (Matsuoka et al.
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From page 303... ...
The other explanations relied on either geometry or time variability. The geometrical explanations required that either the reprocessor or the radiation field be non-spherical The time variability explanation relied on the fact that the region responsible for the iron line was most likely several light days from the nucleus and thus the observer, who sees the average over the whole iron emission line region, was seeing enhanced iron line radiation due to a brightening in the continuum that occurred prior to the observations lit up the Fe line producing region and had decayed away.
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From page 304... ...
Fluorescence lines originating in an accretion disk should be broad and show velocity shifts which are easily resolved with detectors with 200 ev resolution. The energies and ratios of recombination lines originating in a photo-ionized plasma (Krolik and Begelman 1988)
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From page 305... ...
Ginga observations of Seyfert galaxies can explore the domain of fast (At < 1~ second) mnability of AGN to emmine me characteristic time scales expect with the innermost regions of an accretion disk around massive blackholes, T ~ SOM6 sec.
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From page 306... ...
1989. Memorei delta Societa Astronomica Italiana 59: 261.
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