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We investigate the effect of including a significant ``binary twin population (binaries with almost equal mass stars, q = M2/M1 > 0.95) for the production of double compact objects and some resulting consequences, including LIGO inspiral rate and some properties of short-hard gamma-ray bursts. We employ very optimistic assumptions on the twin fraction (50%) among all binaries, and therefore our calculations place an upper limits on the influence of twins on double compact object populations. We show that for LIGO the effect of including twins is relatively minor: although the merger rates does indeed increase when twins are considered, the rate increase is fairly small (1.5). Also, chirp mass distribution for double compact objects formed with or without twins are almost indistinguishable. If double compact object are short-hard GRB progenitors, including twins in population synthesis calculations does not alter significantly the earlier rate predictions for the event rate. However, for one channel of binary evolution, introducing twins more than doubles the rate of ``very prompt NS-NS mergers (time to merger less than 1 Myr) compared to models with the ``flat q distribution. In that case, 70% of all NS-NS binaries merge within 100 Myr after their formation, indicating a possibility of a very significant population of ``prompt short-hard gamma-ray bursts, associated with star forming galaxies. We also point out that, independent of assumptions, fraction of such prompt neutron star mergers is always high, 35--70%. We note that recent observations (e.g., Berger et al.) indicate that fraction of short-hard GRBs found in young hosts is at least 40% and possibly even 80%.
We consider the spatial offsets of short hard gamma-ray bursts (SHBs) from their host galaxies. We show that all SHBs with extended duration soft emission components lie very close to their hosts. We suggest that NS-BH binary mergers offer a natural
We present the first global model of prompt emission from a short gamma-ray burst that consistently describes the evolution of the central black-hole (BH) torus system, the propagation of the jet through multi-component merger ejecta, the transition
Long-duration gamma-ray bursts (LGRBs) are the signatures of extraordinarily high-energy events occurring in our universe. Since their discovery, we have determined that these events are produced during the core-collapse deaths of rare young massive
We present the results of numerical simulations of the prompt emission of short-duration gamma-ray bursts. We consider emission from the relativistic jet, the mildly relativistic cocoon, and the non-relativistic shocked ambient material. We find that
We report the discovery of a transient and fading hard X-ray emission in the BATSE lightcurves of a sample of short gamma-ray bursts. We have summed each of the four channel BATSE light curves of 76 short bursts to uncover the average overall tempora