Suzaku Observations of the Galaxy Cluster 1RXS J0603.3+4214:
  Implications of Particle Acceleration Processes in "Toothbrush" Radio Relic
  We present the results of Suzaku observations of the galaxy cluster 1RXS
J0603.3+4214 with "toothbrush" radio relic. Although a shock with Mach number
$M \simeq 4$ is expected at the outer edge of the relic from the radio
observation, our temperature measurements of the intracluster medium indicate a
weaker temperature difference than what is expected. The Mach number estimated
from the temperature difference at the outer edge of the relic is $M \simeq
1.5$, which is significantly lower than the value estimated from the radio data
even considering both statistical and systematic errors. This suggests that a
diffusive shock acceleration theory in the linear test particle regime, which
is commonly used to link the radio spectral index to the Mach number, is
invalid for this relic. We also measured the temperature difference across the
western part of the relic, where a shock with $M \simeq 1.6$ is suggested from
the X-ray surface brightness analysis of the XMM-Newton data, and obtained
consistent results in an independent way. We searched for the non-thermal
inverse Compton component in the relic region and the resultant upper limit on
the flux is $2.4 \times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$ in the 0.3-10 keV
band. The lower limit of the magnetic field strength becomes 1.6 $\mu$G, which
means that magnetic energy density could be more than a few $\% $ of the
thermal energy.
