SIMBAD references

Recent studies of lensing clusters reveal that it might be fairly common for a galaxy cluster that the X-ray centre has an obvious offset from its gravitational centre which is measured by strong lensing. We argue that if these offsets exist, then X-rays and lensing are indeed measuring different regions of a cluster, and may thus naturally result in a discrepancy in the measured gravitational masses by the two different methods. Here we investigate theoretically the dynamical effects of such lensing-X-ray offsets and compare with observational data. We find that for typical values, the offset alone can give rise to a factor of 2 difference between the lensing and X-ray-determined masses for the core regions of a cluster, suggesting that such `offset effect' may play an important role and should not be ignored in our dynamical measurements of clusters.