Line-of-Sight Anisotropies within X-ray Luminous Cluster Samples

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We present the results from two-point spatial correlation analyses on X-ray confirmed northern Abell clusters. The cluster samples are subsets of a volume-limited ROSAT All-Sky Survey study of 294 Abell clusters of which 240 are X-ray luminous. We examined magnitude- and volume-complete samples for differences according to richness and X-ray luminosity. For R>=1 clusters, we find r₀ = 22h-1Mpc and gamma = -1.7, which is consistent with previous analyses of visually selected clusters. We also find no indications of line-of-sight anisotropies. For R >= 0 clusters, we find r₀= 17.5h-1Mpc which is considerably lower than recent determinations of r₀ for similar X-ray bright cluster samples (e.g. the XBACs and the RASS1 clusters). All of the R>=0 X-ray confirmed samples, including the XBACs and RASS1 clusters, show line-of-sight anisotropies. Since X-ray emissions confirm a cluster's reality, we conclude that these anisotropies are not the result of spuriously selected clusters. We also examine the Abell clusters for the depedence of r₀ and gamma on X-ray luminosity, and find no evidence for r₀ to grow with increasing X-ray luminosity thresholds. This is contrary to similar Lₓ vs. r₀ analyses of the RASS1 and XBACs cluster samples. We describe selection effects within the flux-limited XBACs and RASS1 samples and suggest how they can affect both the size of r₀ and its dependence on Lₓ.