Astron. Astrophys. 331, L57-L60 (1998)

Letter to the Editor

Non-thermal pair model for the radio-galaxy Centaurus A

A.Marcowith ^{1, 2}, G. Henri ² and N. Renaud <sup>2

1</sup> Max-Planck-Institut für Kernphysik, Postfach 10 39 80, D-69029 Heidelberg, Germany,
² Laboratoire d'Astrophysique de l'Observatoire de Grenoble, Université J. Fourier, BP 53, F-38041 Grenoble Cedex 9, France

Received 16 September 1997 / Accepted 30 October 1997

Abstract

In this letter we consider the production of hard X-ray spectrum of the radio galaxy Centaurus A by a relativistic electron-positron beam scattering soft photons coming from an accretion disk. The spectral break of order of 0.7 observed at keV in the 1991 high emission state is explained by absorption of soft gamma-ray photons. The misaligned nature of the relativistic jet explains a redshifted spectral break with regard to pair creation energy threshold. We fit the data with a jet direction making an angle of with the line of sight. We also consider lower Thomson optical depth solutions, and we apply them to the 1992-1994 low state of activity of the source.

Key words: galaxies: active galaxies: individual Cen A radiation mechanisms: nonthermal Gamma-rays: theory

Send offprint requests to: G. Henri

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Contents

• 1. Introduction
• 2. The high energy model for extragalactic sources
  • 2.1. The "two-flow" model
  • 2.2. The high energy spectrum
  • 2.3. The pair model scenario
• 3. Comparisons to the Centaurus A X-ray spectrum
  • 3.1. The parameters of the model
  • 3.2. A red-shifted spectral break
  • 3.3. Low states of activity
• 4. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: March 3, 1998
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