X-ray mass segregation effect in GCs. III. M28

The catalog contains 502 X-ray sources within an area of ~475arcmin^2^, and more than 90% of these sources are first detected in this cluster. We find significant dips in the radial distribution profiles of X-ray sources in M28, and the projected distance and width of the distribution dip for bright (L_X_>~4.5x10^30^erg/s) X-ray sources are larger than for faint (L_X_<~4.5x10^30^erg/s) sources.

Fitting with the "generalized King model" gives a slightly larger average mass for the bright sources (1.30+/-0.15M_{sun}_) than for the faint ones (1.09+/-0.14M_{sun}_), which supports a universal delay in mass segregation between heavy objects in globular clusters. We show that the dynamical age of M28 is comparable to that of Terzan 5 and much smaller than that of 47 Tuc, but M28 is evolving faster (i.e., with a shorter two-body relaxation timescale) than 47 Tuc.