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We present a new mass estimate of a well-studied gravitational lensingcluster, Abell 1689, from deep Chandra observations with a total exposure of200 ks. Within r=200 h-1 kpc, the X-ray mass estimate is systematically lowerthan that of lensing by 30-50%. At r>200 h-1 kpc, the mass density profilesfrom X-ray and weak lensing methods give consistent results. The most recentweak lensing work suggest a steeper profile than what is found from the X-rayanalysis, while still in agreement with the mass at large radii. Previousstudies have suggested that cooler small-scale structures can bias X-raytemperature measurements or that the northern part of the cluster is disturbed.We find these scenarios unlikely to resolve the central mass discrepancy sincethe former requires 70-90% of the space to be occupied by these cool structuresand excluding the northern substructure does not significantly affect the totalmass profiles. A more plausible explanation is a projection effect. We alsofind that the previously reported high hard-band to broad-band temperatureratio in A1689, and many other clusters observed with Chandra, may be resultingfrom the instrumental absorption that decreases 10-15% of the effective area at~1.75 keV.

Discrepant Mass Estimates in the Cluster of Galaxies Abell 1689