The Coalescence Rate of Double Neutron Star Systems

We estimate the coalescence rate of close binaries with two neutron stars(NS) and discuss the prospects for the detection of NS-NS inspiral events byground-based gravitational-wave observatories, such as LIGO. We derive theGalactic coalescence rate using the observed sample of close NS-NS binaries(PSR B1913+16 and PSR B1534+12) and examine in detail each of the sources ofuncertainty associated with the estimate. Specifically, we investigate (i) thedynamical evolution of NS-NS binaries in the Galactic potential and thevertical scale height of the population, (ii) the pulsar lifetimes, (iii) theeffects of the faint end of the radio pulsar luminosity function and theirdependence on the small number of observed objects, (iv) the beaming fraction,and (v) the extrapolation of the Galactic rate to extragalactic distancesexpected to be reachable by LIGO. We find that the dominant source ofuncertainty is the correction factor (up to about 200) for faint (undetectable)pulsars. All other sources are much less important, each with uncertaintyfactors smaller than 2. Despite the relatively large uncertainty, the derivedcoalescence rate is approximately consistent with previously derived upperlimits, and is more accurate than rates obtained from population studies. Weobtain a most conservative lower limit for the LIGO II detection rate of 2events per year. Our upper limit on the detection rate lies between 300 to morethan 1000 events per year.Comment: 40 pages, 7 figures, a few clarifying comments added. Accepted for publication in Ap