The MAVERIC Survey: Dynamical Origin of Radio Sources in Galactic Globular Clusters

We investigate potential correlations between radio source counts (after background corrections) of 22 Galactic globular clusters (GCs) from the MAVERIC survey and the stellar encounter rates (Gamma) and masses (M) of the GCs. Applying a radio luminosity limit of L-lim = 5.0 x 10(27) erg s(-1), we take a census of radio sources in the core and those within the half-light radius of each cluster. By following a maximum likelihood method and adopting a simplified linear model, we find an unambiguous dependence of core radio source counts on Gamma and/or M at 90% confidence, but no clear dependence of source counts within the half-light radius on either Gamma or M. Five of the identified radio sources in GC cores above our adopted limit are millisecond pulsars or neutron star X-ray binaries, the dependence of which on Gamma is well known, but another is a published black hole (BH) X-ray binary candidate, and 10 others are not identified. Accounting for these verified cluster members increases the significance of the correlation with M and/or Gamma (to 99% confidence) for fits to core and half-light region source counts, while excluding a dependence on Gamma alone at 90% (core) and 68% (half-light) confidence. This is consistent with published dynamical simulations of GC BH interactions that argue Gamma will be a poor predictor of the distribution of accreting BHs in GCs. Future multiwavelength follow-up to verify cluster membership will enable stronger constraints on the dependence of radio source classes on cluster properties, promising a new view on the dynamics of BHs in GCs.

Automated summary

The study investigates potential correlations between radio source counts of 22 GCs and their stellar encounter rates and masses. It found a clear dependence of core radio source counts on Gamma and/or M, but no clear dependence on source counts within the half-light radius. Verified cluster members increased the significance of the correlation with M and/or Gamma, while excluding a dependence on Gamma alone.