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

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Letter to the Editor

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

A.Marcowith 1, 2, G. Henri 2 and N. Renaud 2

1 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


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 [FORMULA] keV in the 1991 high emission state is explained by [FORMULA] 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 [FORMULA] 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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© European Southern Observatory (ESO) 1998

Online publication: March 3, 1998