Title:Short gamma-ray bursts from dynamically-assembled compact binaries in globular clusters: pathways, rates, hydrodynamics and cosmological setting

Abstract:We present a detailed assessment of the dynamical pathways leading to the coalescence of compact objects in Globular Clusters (GCs) and Short Gamma-Ray Burst (SGRB) production. We consider primordial binaries, dynamically formed binaries (through tidal two-body and three-body exchange interactions) and direct impacts of compact objects (WD/NS/BH). We show that if the primordial binary fraction is small, close encounters dominate the production rate of coalescing compact systems. We find that the two dominant channels are the interaction of field NSs with dynamically formed binaries, and two-body encounters. We then estimate the redshift distribution and host galaxy demographics of SGRB progenitors, and find that GCs can provide a significant contribution to the overall observed rate.
We have carried out hydrodynamical modeling of evolution of close stellar encounters with WD/NS/BH, and show that there is no problem in accounting for the energy budget of a typical SGRB. The particulars of each encounter are variable and lead to interesting diversity: the encounter characteristics are dependent on the impact parameter, in contrast to the merger scenario; the nature of the compact star itself can produce very different outcomes; the presence of tidal tails in which material falls back onto the central object at later times is a robust feature of these calculations, with the mass involved being larger than for binary mergers. It is thus possible to account generically in this scenario for a prompt episode of energy release, as well as for activity many dynamical time scales later (abridged).