(ed.). Gravitational waves (IOP, 2001)(422s).

Sources detectable from ground and from space 45Table 4.1. The range for detecting a 2 × 1.4M ⊙ NS binary coalescence. The threshold fordetection is taken to be 5σ . The binary and detector orientations are assumed optimum.The average S/N ratio for randomly oriented systems is reduced from the optimum by1/ √ 5.Detector: TAMA300 GEO600 LIGO I VIRGO LIGO IIRange (S/N = 5) 3 Mpc 14 Mpc 30 Mpc 36 Mpc 500 Mpcabout 10 3 M ⊙ , the binary will go all the way to coalescence within the one-yearobservation.Chirping binary systems are more easily detectable than gravitationalcollapse events because one can model with great accuracy the gravitationalwaveform during the inspiral phase. There will be radiation, possibly withconsiderable energy, during the poorly understood plunge phase (when the objectsreach the last stable orbit and fall rapidly towards one another) and during themerger event, but the detectability of such systems rests on tracking their orbitalemissions.The major uncertainty about this kind of source is the event rate. Currentpulsar observations suggest that there will be ∼1 coalescence per year of a Hulse-Taylor binary out to about 200 Mpc. This is a lower limit on the event rate, since itcomes from systems we actually observe. It is possible that there are other kindsof binaries that we have no direct knowledge of, which will boost the event rate.Theoretical modelling of binary populations gives a wide spectrum ofmutually inconsistent predictions. Some authors [14] suggest that there may bea large population that escapes pulsar surveys but brings the nearest neutron starcoalescence in one year as far as 30 Mpc, only slightly farther than the Virgocluster; but other models [15] put the rate near to the observational limit.The most exciting motivation for detecting coalescing binaries is that theycould be associated with gamma-ray bursts. The event rates are consistent,and neutron stars are able to provide the required energy. If gamma-burstsare associated with neutron-star coalescence, then observations of coalescenceradiation should be followed within a second or so by a strong gamma-ray burst.LISA will see a few chirping binaries in the Galaxy, but the sensitivity ofthe first generation of ground-based detectors is likely to be too poor to see manysuch events (see table 4.1).A certain fraction of such systems could contain black holes instead ofneutron stars. In fact black holes should be overrepresented in binary systems(relative to their birth rate) because their formation is much less likely to disrupta binary system (there is much less mass lost) than the formation of a neutronstar would be. Pulsar observations have not yet turned up a black-hole/neutronstarsystem, and of course one does not expect to see binary black holes