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Session 28 - Diffuse Gamma-Ray Emission & Gamma-Ray Bursts.
Oral session, Monday, January 13
Harbour B,
We propose a new cosmological scenario of gamma-ray burst (GRB) origin, which envisions the production of GRBs in the evolved galactic nuclei: The abundant compact stellar remnants (CSRs) such as neutron stars (NSs) and stellar mass black holes (BHs), as well as binaries consisting of them, are formed in the central parts of the galactic nuclei in due course of the dynamical evolution of the nuclei through close encounters/collisions, coalescence, and SN explosions of ordinary stars. In compact galactic nuclei, random encounters of CSR, which are accompanied by gravitational wave radiation, result in the radiative binary formation and in further CSR coalescence, and this would produce a GRB episode. The rate of GRBs per unit comoving volume is found to be \dot n_0 \simeq 3.7\cdot10^-8\, \left(\fracM_g10^11\,M_\sun\right)^-1 \left(\fracM10^7 M_\sun\right)^17/14 \left(\fracR0.1\,pc\right)^-31/14\: \frac\mboxevents\mboxyr Mpc^3, where M and R are the core mass and core radius of the nucleus, respectively, M_g is the galactic mass, and the space density of galaxies is assumed to contribute a fraction Ømega_g=10^-2 of the critical density. The value of \dot n_0 appears to be consistent with the rate of NS merging in galaxies required to explain the GRB phenomenon. The binaries formed by radiative capture in the evolved galactic nuclei are short-living compared to the age of the Universe. This makes a difference with the standard cosmological scenario where the NS binaries are generally long-living. The signature of the proposed scenario for the GRB origin is the gravitational wave radiation that causes the coalescence of CSR in due course of their close encounters. The spiralling-in that accompanies the process of close binary formation and evolution results in the specific pattern of gravitational radiation, which is distinguishable from gravitational radiation of other origins. In principle, the recurrent GRBs (so far not detected) could be observable from a host galactic nucleus if it is dense enough.
