Chandra observation of the most interesting cluster in the Universe
  Chandra has recently observed 1E0657-56, a hot merging system at z=0.3 (the ``bullet'' cluster), for 500 ks. I present some of the findings from this dataset. The cluster exhibits a prominent bow shock with M=3.0+-0.4 (one of only two known M>>1 shock fronts), which we use for a first test of the electron-ion equilibrium in an intergalactic plasma. The temperatures across the shock are consistent with instant shock-heating of the electrons; at 95% confidence, the equilibration timescale is much shorter than the collisional Spitzer value. Global properties of 1E0657-56 are also remarkable. Despite being extremely unrelaxed, the cluster fits well on the Lx-T relation, yet its total mass estimated from the M-T relation is more than twice the value measured from lensing. This is consistent with simulations predicting that in the middle of a merger, global temperature and X-ray luminosity may be temporarily boosted by a large factor. 
Maxim Markevitch (CfA)