Expected Coalescence Rate of Double Neutron Stars for Ground Based Interferometers

In this paper we present new estimates of the coalescence rate of neutron star binaries in the local universe and we discuss its consequences for the first generations of ground based interferometers. Our approach based on both evolutionary and statistical methods gives a galactic merging rate of 1.7 10$^{-5}$ yr$^{-1}$, in the range of previous estimates 10$^{-6}$ - 10$^{-4}$ yr$^{-1}$. The local rate which includes the contribution of elliptical galaxies is two times higher, in the order of 3.4 10$^{-5}$ yr$^{-1}$. We predict one detection every 148 and 125 years with initial VIRGO and LIGO, and up to 6 events per year with their advanced configuration. Our recent detection rate estimates from investigations on VIRGO future improvements are quoted.Comment: talk given at the GWDAW9 (Annecy, 2004) to be published in CQ

Advanced VIRGO: detector optimization for gravitational waves by inspiralling binaries

For future configurations, we study the relation between the abatement of the noise sources and the Signal to Noise Ratio (SNR) for coalescing binaries. Our aim is not the proposition of a new design, but an indication of where in the bandwidth or for which noise source, a noise reduction would be most efficient. We take VIRGO as the reference for our considerations, solely applicable to the inspiralling phase of a coalescing binary. Thus, only neutron stars and small black holes of few solar masses are encompassed by our analysis. The contributions to the SNR given by final merge and quasi-normal ringing are neglected. It is identified that i) the reduction in the mirror thermal noise band provides the highest gain for the SNR, when the VIRGO bandwidth is divided according to the dominant noises; ii) it exists a specific frequency at which lies the potential largest increment in the SNR, and that the enlargement of the bandwidth, where the noise is reduced, produces a shift of such optimal frequency to higher values; iii) the abatement of the pendulum thermal noise provides the largest, but modest, gain, when noise sources are considered separately. Our recent astrophysical analysis on event rates for neutron stars leads to a detection rate of one every 148 or 125 years for VIRGO and LIGO, respectively, while a recently proposed and improved, but still conservative, VIRGO configuration would provide an increase to 1.5 events per year. Instead, a bi-monthly event rate, similar to advanced LIGO, requires a 16 times gain. We analyse the 3D (pendulum, mirror, shot noises) parameter space showing how such gain could be achieved.Comment: Change of title (Virgo detector optimization for gravitational waves by coalescing binaries) and partially of text. 6 figure

Expected coalescence rates of NS-NS binaries for laser beam interferometers

The coalescence rate of two neutron stars (NS) is revisited. For estimation of the number of bound NS-NS and the probability of their coalescence in a timescale $\tau$, the galactic star formation history, directly derived from observations, and the evolution of massive stars are considered. The newly established galactic merging rate is $(1.7\pm 1.0) \times 10^{-5} yr^{-1}$, while the local merging rate, including the contribution of elliptical galaxies, is about a factor of two higher, $3.4 \times 10^{-5} yr^{-1}$. Using the present data basis on galaxy distribution in the local universe and the expected sensitivity of the first generation of laser beam interferometers, we estimate that one event should occur every 125 years for LIGO and one event each 148 years for VIRGO. The situation is considerably improved for advanced-LIGO since we predict that 6 events per year should be detected whereas for a recently proposed VIRGO new configuration, the event rate might increase up to 3 events every two years.Comment: 15 pages, 3 figures accepted for publication in IJMP