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Abstract: We review new Chandra and HST observations of the core collapsed cluster NGC 6397 as a guide to understanding the compact binary (CB) populations in core collapse globulars. New cataclysmic variables (CVs) and main sequence chromospherically active binaries (ABs) have been identified, enabling a larger sample for comparison of the L x , F x /F V and X-ray vs. optical color distributions. Comparison of the numbers of CBs with L x ≳1031 ergs−1 in 4 core collapse vs. 12 King model clusters reveals that the specific frequency S X (number of CBs per unit cluster mass) is enhanced in core collapse clusters, even when normalized for their stellar encounter rate. Although core collapse is halted by the dynamical heating due to stellar (and binary) interaction with CBs in the core, we conclude that production of the hardest CBs – especially CVs – is enhanced during core collapse. NGC 6397 has its most luminous CVs nearest the cluster center, with two newly discovered very low luminosity (old, quiescent) CVs far from the core. The active binaries as well as neutron star systems (MSP and qLMXB) surround the central core. The overall CB population appears to be asymmetric about the cluster center, as in several other core collapse clusters observed with Chandra, suggesting still poorly understood scattering processes. [Copyright &y& Elsevier]

Observations by the Swift gamma-ray-burst (GRB) mission located short GRBs in (or near) elliptical galaxies, that are no longer active in star formation. This suggested that short GRBs are produced when neutron stars (NSs) merge with other NSs or with black holes (BHs). However, the spatial offset of some short GRBs from their host galaxies is not consistent with double-neutron-star (DNS) systems formed from massive binary stars, which appear to remain in galactic disks. Instead, short GRBs may arise from NS mergers in compact binary systems that are naturally produced in globular clusters, in which extreme densities of very old stars can create and exchange compact binaries efficiently. Here we present a simple scaling from the DNS binary observed in the globular cluster M15 in our own Galaxy to the numbers expected for globular clusters around galaxies generally. We present numerical simulations that demonstrate that DNS production in globular clusters may account for ∼10–30% of the observed short GRBs. The much more numerous DNS merger rates predicted for galactic disks suggests their associated short GRBs are significantly more beamed, perhaps by the aligned spins and greater magnetic field of their secondary NSs. [ABSTRACT FROM AUTHOR]