title: Measuring the spin of black holes in binary systems using gravitational waves.
abstract: Compact binary coalescences are the most promising sources of gravitational waves (GWs) for ground-based detectors. Binary systems containing one or two spinning black holes are particularly interesting due to spin-orbit (and eventual spin-spin) interactions and the opportunity of measuring spins directly through GW observations. In this Letter, we analyze simulated signals emitted by spinning binaries with several values of masses, spins, orientations, and signal-to-noise ratios, as detected by an advanced LIGO-Virgo network. We find that for moderate or high signal-to-noise ratio the spin magnitudes can be estimated with errors of a few percent (5%-30%) for neutron star-black hole (black hole-black hole) systems. Spins' tilt angle can be estimated with errors of 0.04 rad in the best cases, but typical values will be above 0.1 rad. Errors will be larger for signals barely above the threshold for detection. The difference in the azimuth angles of the spins, which may be used to check if spins are locked into resonant configurations, cannot be constrained. We observe that the best performances are obtained when the line of sight is perpendicular to the system's total angular momentum and that a sudden change of behavior occurs when a system is observed from angles such that the plane of the orbit can be seen both from above and below during the time the signal is in band. This study suggests that direct measurement of black hole spin by means of GWs can be as precise as what can be obtained from x-ray binaries.
authors.affiliation: Massachusetts Institute of Technology, 185 Albany Street, Cambridge, Massachusetts 02138, USA.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Vitale
authors.affiliation: Massachusetts Institute of Technology, 185 Albany Street, Cambridge, Massachusetts 02138, USA.
authors.forename: Ryan
authors.initials: R
authors.lastname: Lynch
authors.affiliation: Nikhef, Science Park 105, Amsterdam 1098XG, The Netherlands and School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, United Kingdom.
authors.forename: John
authors.initials: J
authors.lastname: Veitch
authors.affiliation: LIGO Laboratory, California Institute of Technology, MC 100-36, Pasadena, California 91125, USA.
authors.forename: Vivien
authors.initials: V
authors.lastname: Raymond
authors.affiliation: ICTP South American Institute for Fundamental Research & Instituto de Física Teórica, Universidade Estadual Paulista, São Paulo, São Paulo 011040-070, Brasil.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Sturani