Exploring the Mass Segregation Effect of X-ray Sources in Globular Clusters. III. Signs of Binary Disruption in M28

Using archival {\it 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 $\sim 475\mathrm{a}\mathrm{r}\mathrm{c}\mathrm{m}\mathrm{i}{\mathrm{n}}^2$, and more than $90\mathrm{\%}$ 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 ($L_{X} \gtrsim 4.5\times 10^{30} {\rm\ erg
,s^{-1}}$)X-raysourcesarelargerthanthefaint($L_{X} \lesssim 4.5\times 10^{30} {\rm\ erg\ ,s^{-1}}$) sources. The “generalized King model” fitting give a slightly larger average mass for the bright sources ($1.30\pm 0.15M_{\odot }$) than the faint sources ($1.09\pm 0.14M_{\odot }$), 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 ($R\lesssim 1.5\mathrm{a}\mathrm{r}\mathrm{c}\mathrm{m}\mathrm{i}\mathrm{n}$) 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.