M. Abramowicz, J. Becker, P. Biermann, A. Garzilli, F. Johansson, and L. Qian. (2008)cite arxiv:0810.3140
Comment: This v2 version replaces the v1 version, submitted on 17 October
2008. The only change is a new section 7 that we have added in order to
comment on the article by Roncadelli, Treves and Turolla (2009), submitted to
the astro-ph server on 8 Jananuary 2009, as arXiv:0901.1093. We have not
changed anything else in the previous version v1.