Astron. Astrophys. 326, 99-107 (1997)

Anisotropic illumination of AGN's accretion disk by a non thermal source

II. General relativistic effects

P.O. Petrucci and G. Henri

Laboratoire d'Astrophysique, Observatoire de Grenoble,B.P 53X, F-38041 Grenoble Cedex, France

Received 4 November 1996 / Accepted 28 April 1997

Abstract

In a previous paper (Henri & Petrucci in press, hereafter Paper I), we have derived a new model in order to explain the UV and X-ray emission of radio quiet AGNs. This model assumes that a point source of relativistic leptons () illuminates the accretion disk of the AGN by Inverse Compton process. This disk is supposed to be simply represented by a finite slab which radiates only the energy reprocessed from the hot source. The radiation field within the hot source region is therefore highly anisotropic, which strongly influences the Inverse Compton process. The different Eddington parameters characterizing the radiative balance of this system have been calculated self-consistently in the Newtonian case (Paper I) giving a universal spectrum for a given inclination angle. In this paper, we take into account relativistic effects by including the gravitational redshift, the Doppler boosting and the gravitational focusing due to the central supermassive black hole. This has the effect of modifying the radial temperature profile in the innermost region of the disk (at some gravitational radii). However, the spectrum is hardly different from that obtained in the Newtonian case, unless the hot source is very close to the black hole. These results are clearly different from standard accretion disk models where the gravitational energy is mainly released in the vicinity of the black hole.

Key words: galaxies: active galaxies: Seyfert accretion, accretion disk ultraviolet: galaxies X-rays: galaxies relativity

Contents

• 1. Introduction
• 2. Relativistic energy balance equations
  • 2.1. The different frames
  • 2.2. Computation of the specific intensity
  • 2.3. Computation of Eddington parameters
• 3. Computation in the Kerr geometry
  • 3.1. The gravitational shifts
  • 3.2. Computation of
  • 3.3. Disk emission spectrum
• 4. Results and discussion
  • 4.1. The set of parameters
  • 4.2. Angular distribution of radiation
  • 4.3. The radial temperature distribution
  • 4.4. Overall spectrum
    • 4.4.1. Influence of the hot source's height
    • 4.4.2. Influence of the inclination angle
• 5. Conclusion
• Appendix A: expression of dS
• Appendix B: Kerr metric case. Expression of dS in the plan
• References

© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998
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