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M. Takizawa (Department of Astronomy, University of Virginia), H. Ohno (Yamagata Junior College, Japan), S. Shibata (Yamagata University, Japan)
Clusters of galaxies contain not only the thermal intracluster medium but also non-thermal high energy particles in intracluster space. One of their direct evidences is existence of non-thermal synchrotron radio halos and relics, which have been observed since 1970s. This indicates that there are non-thermal electrons with energy of ~ GeV in intracluster space. However, origin of non-thermal electrons and their acceleration mechanisms are still unclear though they are probably related with some active phenomena in clusters such as cluster mergers, AGNs, AGNs' jets, and/or star burst in the member galaxies.
We consider resonant scattering with random Alfven waves as an acceleration process of electrons in the intracluster space. Steady state momentum distribution function of the non-thermal electrons are calculated for given spectra of the turbulent Alfven waves. The synchrotron radio spectrum produced by the obtained electron distribution is compared with the observed one of the Coma radio halo. We find that the observed radio spectrum of Coma is well reproduced when the spectral index of the turbulent Alfven waves is ~ 2.8. The obtained energy spectrum of Alfven waves is steeper than that expected from the turbulence theory. This suggests that back reaction of the particle acceleration plays significant role as a energy sink of turbulent Alfven waves. It is most likely that cluster mergers create the turbulence and seed relativistic electrons.
The author(s) of this abstract have provided an email address for comments about the abstract: mt9r@virginia.edu