Timing of millisecond pulsars in NGC 6752: Evidence for a high mass-to-light ratio in the cluster core

Using pulse timing observations, we have obtained precise parameters, including positions with similar to20 mas accuracy, of five millisecond pulsars in NGC 6752. Three of them, located relatively close to the cluster center, have line-of-sight accelerations larger than the maximum value predicted by the central mass density derived from optical observation, providing dynamical evidence for a central mass-to-light ratio greater than or similar to10, much higher than for any other globular cluster. It is likely that the other two millisecond pulsars have been ejected out of the core to their present locations at 1.4 and 3.3 half-mass radii, respectively, suggesting unusual nonthermal dynamics in the cluster core.