Short Gamma-Ray Bursts (SGRBs) are expected to form from the coalescence of compact binaries, either of primordial origin or from dynamical interactions in globular clusters. In this paper, we investigate the possibility that the offset and afterglow
brightness of a SGRB can help revealing the origin of its progenitor binary. We find that a SGRB is likely to result from the primordial channel if it is observed within 10 kpc from the center of a massive galaxy and shows a detectable afterglow. The same conclusion holds if it is 100 kpc away from a small, isolated galaxy and shows a weak afterglow. On the other hand, a dynamical origin is suggested for those SGRBs with observable afterglow either at a large separation from a massive, isolated galaxy or with an offset of 10-100 kpc from a small, isolated galaxy. We discuss the possibility that SGRBs from the dynamical channel are hosted in intra-cluster globular clusters and find that GRB 061201 may fall within this scenario.
Anisotropic gravitational radiation from a coalescing black hole binary is known to impart recoil velocities of up to ~1000 km/s to the remnant black hole. In this context, we study the motion of a recoiling black hole inside a galaxy modelled as an
Hernquist sphere, and the signature that the hole imprints on the hot gas, using N-body/SPH simulations. Ejection of the black hole results in a sudden expansion of the gas ending with the formation of a gaseous core, similarly to what is seen for the stars. A cometary tail of particles bound to the black hole is initially released along its trail. As the black hole moves on a return orbit, a nearly spherical swarm of hot gaseous particles forms at every apocentre: this feature can live up to ~ 100 Myr. If the recoil velocity exceeds the sound speed initially, the black hole shocks the gas in the form of a Mach cone in density near each super-sonic pericentric passage. We find that the X-ray fingerprint of a recoiling black hole can be detected in Chandra X-ray maps out to a distance of Virgo. For exceptionally massive black holes the Mach cone and the wakes could be observed out to a few hundred of Mpc. Detection of the Mach cone is found to become of twofold importance: i) as a probe of high-velocity recoils and ii) as an assessment of the scatter of the mass-sigma relation at large black hole masses.
We study the process of dynamical capture of a millisecond pulsar (MSP) by a single or binary IMBH, simulating various types of single-binary and binary-binary encounters. It is found that [IMBH,MSP] binaries form over cosmic time in a cluster, via e
ncounters of wide--orbit binary MSPs off the single IMBH, and at a lower pace, via interactions of (binary or single) MSPs with the IMBH orbited by a typical cluster star. The formation of an [IMBH,MSP] system is strongly inhibited if the IMBH is orbited by a stellar mass black hole. The [IMBH,MSP] binaries that form are relatively short-lived, $lsim 10^{8-9}$ yr, since their orbits decay via emission of gravitational waves. The detection of an [IMBH,MSP] system has a low probability of occurrence, when inferred from the current sample of MSPs in GCs. If next generation radio telescopes, like SKA, will detect an order of magnitude larger population of MSP in GCs, at least one [IMBH,MSP] is expected. Therefore, a complete search for low-luminosity MSPs in the GCs of the Milky Way with SKA will have the potential of testing the hypothesis that IMBHs of order $100 msun$ are commonly hosted in GCs.
