We present a Chandra observation of the merging cluster of galaxies Abell
2744. The cluster shows strong evidence for an ongoing major merger which we
believe to be responsible for the radio halo. X-ray emission and temperature
maps of the cluster, combined with the spatial and redshift distribution of the
galaxies, indicate a roughly north-south axis for the merger, with a
significant velocity component along the line of sight. The merger is occurring
at a very large velocity, with M = 2-3. In addition, there is a small merging
subcluster toward the northwest, unrelated to the major merger, which shows
evidence of a bow shock. A hydrodynamical analysis of the subcluster indicates
a merger velocity corresponding to a Mach number of ~1.2, consistent with a
simple infall model. This infalling subcluster may also be re-exciting
electrons in the radio halo. Its small Mach number lends support to turbulent
reacceleration models for radio halo formation.Comment: 8 pages, 6 figures (5 color). Submitted to MNRA