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

Abstract

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 Xray sources within an area of ∼ 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 4.5×10 30 erg s −1 ) X-ray sources are larger than the faint (L X 4.5 × 10 30 erg s −1 ) sources. The "generalized King model" fitting give a slightly larger average mass for the bright sources (1.30 ± 0.15 M ⊙ ) than the faint sources (1.09 ± 0.14 M ⊙ ), 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 1.5 ′ ) 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.

Exploring the Mass Segregation Effect of X-Ray Sources in Globular Clusters. IV. Evidence of Black Hole Burning in ω Centauri

“…On the other hand, we found significant distribution dips for X-ray sources in 47 Tuc, which is consistent with the mass segregation delay of heavy objects in GCs (Cheng et al 2019a). Using the mass segregation effect of X-ray sources as an indicator of cluster dynamical age, we also show that there is evident acceleration effect for cluster dynamical evolution by tidal stripping in Terzan 5 (Cheng et al 2019b) and M28 (Cheng et al 2020). Besides, we found an abnormal deficiency of X-ray sources in the central region (R 1.5 ′ ) of M28 with respect to its outskirts, which indicates that M28 has suffered an early phase of primordial binary disruption within its central region, and that BHS may play an important role in creating and maintaining this peculiar distribution of X-ray sources in M28 (Cheng et al 2020).…”

“…On the other hand, the threshold value of P B also offers us a criterion to calculate the limiting detection sensitivity across the FoV of ω Cen. The resulting sensitivity maps were found to be very useful in estimating the contribution of cosmic X-ray background (CXB) sources and Galactic interlopers (Cheng et al 2019b(Cheng et al , 2020.…”

On Socially Distant Neighbors: Using Binaries to Constrain the Density of Objects in the Galactic Center

“…For example, Geller et al ( 2013) and de suggest that, contrary to the effects of mass segregation, the binary fraction in the globular cluster NGC 1818 decreases radially towards the center because binary disruption dominates closer to the core. Cheng et al (2020) discuss a similar competition between mass segregation and binary disruption in the context of the globular cluster M28's X-ray binary population. While N-body simulations are necessary to obtain a comprehensive picture of GC binary demographics over time, based on these calculations, we expect that mass segregation plays a secondary role to evaporation in shaping the distribution of binaries in the GC, in particular the binary fraction as a function of distance from the SMBH.…”

Properties of Cataclysmic Variables in Globular Clusters

“…Interestingly, spectra of such CVs could be relatively easy to obtain, since crowding should not be a big problem in the outer parts. With respect to observations, Cheng et al (2019a [164]; 2019b [165]; 2020 [166]) recently investigated the phenomenon of mass segregation in the GCs 47 Tuc, Terzan 5 and M28. These authors confirmed that there are some X-ray sources located outside the half-light radii and showed that the radial distribution of X-ray sources in these clusters is bimodal, with features similar to those found in the radial distribution of blue stragglers, they being modulated by mass segregation of primordial binaries.…”