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Authors: Emanuele Berti, Alessandra Buonanno, Clifford M. Will

Date: Tue, 5 Apr 2005

Abstract: We study parameter estimation for inspiralling compact binaries of massive black holes (MBH), and for inspirals of neutron stars into intermediate-mass black holes, using LISA. We include non-precessional spin effects. We work both in Einstein's theory and in alternative theories of gravity of the scalar-tensor and massive-graviton types. Inclusion of spin terms in MBH binaries has little effect on the angular resolution or on distance determination accuracy, but it degrades the estimation of intrinsic binary parameters such as chirp mass and reduced mass by between one and two orders of magnitude. The bound on the coupling parameter of scalar-tensor gravity is significantly reduced by the presence of spin couplings, while the reduction in the graviton-mass bound is milder. LISA will measure the luminosity distance of MBHs to better than ~10% out to z~4 for a (10ˆ6+10ˆ6) Msun binary, and out to z~2 for a (10ˆ7+10ˆ7) Msun binary. The chirp mass of a MBH binary can always be determined with excellent accuracy. Ignoring spin effects, the reduced mass can be measured within ~1% out to z=10 and beyond for a (10ˆ6+10ˆ6) Msun binary, but only out to z~2 for a (10ˆ7+10ˆ7) Msun binary. Present-day MBH coalescence rate calculations indicate that most detectable events should originate at z~2-6: at these redshifts LISA can be used to measure the two black hole masses and their luminosity distance with sufficient accuracy to probe the merger history of MBHs. If the low-frequency LISA noise can only be trusted down to 10ˆ-4 Hz, parameter estimation for MBHs (and LISA's ability to perform reliable cosmological observations) will be significantly degraded.

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