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Astron. Astrophys. 325, 19-26 (1997)

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A statistical method of testing the gamma ray emission mechanisms of blazars

Xinyu Chi * and Enoch C.M. Young

Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong

Received 11 October 1996 / Accepted 3 February 1997


Models for generation of high energy gamma rays in blazars can be classified into two types of mechanisms in the jet comoving frame: relativistic electron scattering on the internal photons or magnetic field (virtual photons) (SIP) and on the external photons (SEP). These two mechanisms are known to result in a significant difference in the beaming effect. In this work, we propose a statistical test for the two types of mechanisms based on the beaming difference. The random variable is taken to be the K-corrected gamma ray to radio flux ratio and its distribution is shown to be a power-law with an index being model-dependent.

The feasibility of such a test is investigated with a limited sample of data which are complied from the EGRET gamma ray survey, low resolution radio surveys and a VLBI radio survey. A correlation study indicates that the VLBI data are more suitable for the purpose than the low resolution data. Due to the limited amount of available data, the current test result is not statistically significant to discriminate the two emission mechanisms. Future generation of high energy gamma ray telescopes are needed to produce a larger sample of data of gamma ray blazars and their simultaneous observations with VLBI are called.

Key words: gamma rays: theory – galaxies: active – quasars: general – radiation mechanisms: nonthermal

* Now at Department of Computer Science, Vanderbilt University, Nashville, TN37235, USA

Send offprint requests to: X. Chi

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© European Southern Observatory (ESO) 1997

Online publication: May 5, 1998