科研之友
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摘要
In the unification scheme for active galactic nuclei, type 1 Seyfert galaxies and type 2 Seyfert galaxies are thought to be intrinsically the same but viewed at different angles. However, the Fe K alpha emission line luminosity of type 1 Seyfert galaxies was found on average to be about twice that of type 2 Seyfert galaxies for a given X-ray continuum luminosity in previous work. We construct an accretion disc-corona model in which a fraction of the energy dissipated in the disc is extracted to heat the corona above the disc. The radiation transfer equation with Compton scattering processes is an integro-differential equation, which is solved numerically for the corona with a parallel plane geometry. We find that the specific intensity of X-ray radiation from the corona changes little with the viewing angle theta when theta is small (nearly face-on), and it is sensitive to theta if the viewing angle is large (theta greater than or similar to 40 degrees). The radiation from the cold disc, mostly in infrared, optical and UV bands, is almost proportional to cos theta when theta less than or similar to 40 degrees, while it decreases more rapidly than cos theta when theta greater than or similar to 40 degrees because of strong absorption in the corona in this case. For Seyfert galaxies, the Fe K alpha line may probably be emitted from the disc irradiated by the X-ray continuum emission. The observed equivalent width difference between type 1 Seyfert galaxies and type 2 Seyfert galaxies can be reproduced by our model calculations, provided the type 1 Seyfert galaxies are observed nearly face-on and the average inclination angle of type 2 Seyfert galaxies is similar to 65 degrees.
- 出版日期2015-5-1
- 单位上海交通大学
