Using archival Chandra observations with a total effective exposure of 323 ks , we derive an updated catalog of point sources in the bulge globular cluster M28 .
The catalog contains 502 X-ray sources within an area of \sim 475 arcmin ^ { 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 , with the projected distance and width of the distribution dip for bright ( L _ { X } \gtrsim 4.5 \times 10 ^ { 30 } { erg s ^ { -1 } } ) X-ray sources are larger than the faint ( L _ { X } \lesssim 4.5 \times 10 ^ { 30 } { erg s ^ { -1 } } ) sources .
The “ generalized King model ” fitting give a slightly larger average mass for the bright sources ( 1.30 \pm 0.15 M _ { \odot } ) than the faint sources ( 1.09 \pm 0.14 M _ { \odot } ) , which support a universal mass segregation delay between heavy objects in GCs .
Compared with 47 Tuc and Terzan 5 , we show that the dynamical age of M28 is comparable to Terzan 5 and much smaller than 47 Tuc , but it is evolving more fast ( i.e. , with smaller two-body relaxation timescale ) than 47 Tuc .
These features may suggest an acceleration effect of cluster dynamical evolution by tidal shock in M28 .
Besides , we find an abnormal deficiency of X-ray sources in the central region ( R \lesssim 1.5 \arcmin ) of M28 than its outskirts , which indicate that M28 may have suffered an early phase of primordial binary disruption within its central region , and mass segregation effect will erase such a phenomenon as cluster evolve to older dynamical age .