Non-Equilibrium Ionization State and Two-Temperature Structure in the
  Bullet Cluster 1E0657-56
  We investigate a non-equilibrium ionization state and an electron-ion
two-temperature structure of the intracluster medium in the merging galaxy
cluster, 1E0657-56 (the Bullet cluster), using a series of N-body and
hydrodynamic simulations. We find that the electron temperature at the shock
layer associated with the X-ray sub peak (bullet) is quite different depending
on the thermal relaxation model between electrons and ions; ~25 keV for the
Coulomb thermal relaxation model and ~45 keV for the instantaneous thermal
relaxation model in the simulations which reproduce the observed X-ray
morphology. Furthermore, both of Fe xxv and Fe xxvi are overabundant compared
with the ionization equilibrium state around the shock layer, and thus, the
intensity ratio between Fe xxv and Fe xxvi K alpha lines are significantly
altered from that in the ionization equilibrium state. We also carry out the
simulations with various sets of merger parameters, and discuss a possible
range of the non-equilibrium effects in this system. Our results could be
tested with future X-ray observations such as Astro-H with better sensitivity
in high energy band.
