...1,2,

Permanent address: Turku University.

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... beta

Note that Vainio & Schlickeiser (1998) defined plasma beta as the ratio of upstream sound speed to the upstream Alfvén speed, which equals $2\beta /\gamma _{\rm g}$ or $6\beta /5$ for $\gamma _{\rm g}=5/3$ in this paper.

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... respectively

Note that this ratio was denoted b² in Vainio & Schlickeiser (1999).

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