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Using a combination of Chandra and XMM observations, we confirmed thepresence of a significant velocity gradient along the NE/E-W/SW direction inthe intracluster gas of the cluster Abell 576. The results are consistent witha previous ASCA SIS analysis of this cluster. The error weighted average overACIS-S3, EPIC MOS 1 & 2 spectrometers for the maximum velocity difference is>3.3E03 km/s at the 90% confidence level, similar to the velocity limitsestimated indirectly for the "bullet" cluster (1E0657-56). The probability thatthe velocity gradient is generated by standard random gain fluctuations withChandra and XMM is <0.1%. The regions of maximum velocity gradient are in CCDzones that have the lowest temporal gain variations. It is unlikely that thevelocity gradient is due to Hubble distance differences between projectedclusters (probability<~0.01%). We mapped the distribution of elementalabundance ratios across the cluster and detected a strong chemicaldiscontinuity using the abundance ratio of silicon to iron, equivalent to avariation from 100% SN Ia iron mass fraction in the West-Northwest regions to32% in the Eastern region. The "center" of the cluster is located at thechemical discontinuity boundary, which is inconsistent with the radiallysymmetric chemical gradient found in some regular clusters, but consistent witha cluster merging scenario. We predict that the velocity gradient as measuredwill produce a variation of the CMB temperature towards the East of the core ofthe cluster that will be detectable by current and near-future bolometers. Themeasured velocity gradient opens for the possibility that this cluster ispassing through a near line-of-sight merger stage where the cores have recentlycrossed.

The Merger in Abell 576: A Line of Sight Bullet Cluster?