Gravitational-wave measurements of the mass and angular momentum of a black hole

A deformed black hole produced in a cataclysmic astrophysical event should undergo damped vibrations which emit gravitational radiation. By fitting the observed gravitational waveform h(t) to the waveform predicted for black-hole vibrations, it should be possible to deduce the hole's mass M and dimensionless rotation parameter a=(c/G)(angular momentum)/M². This paper estimates the accuracy with which M and a can be determined by optimal signal processing of data from laser-interferometer gravitational-wave detectors. It is assumed that the detector noise has a white spectrum and has been made Gaussian by cross correlation of detectors at different sites. Assuming, also, that only the most slowly damped mode (which has spheroidal harmonic indices l=m=2) is significantly excited---as probably will be the case for a hole formed by the coalescence of a neutron-star binary or a black-hole binary---it is found that the one-sigma uncertainties in M and a are {Δ}M/M{}2.2ρ^-1(1-a)0.45, {Δ}a{}5.9ρ^-1(1-a)1.06, where {ρ}{}hₛ({π}Sₕ{)}^{{{-}}1/2}$ (1-a${)}^{{{-}}0.22}. Here ρ is the amplitude signal-to-noise ratio at the output of the optimal filter,{h}ₛis the wave's amplitude at the beginning of the vibrations, f is the wave's frequency (the angular frequency ω divided by 2π), and{S}ₕ$ is the frequency-independent spectral density of the detectors' noise. These formulas for {Δ}M and {Δ}a are valid only for {ρ}{}10. Corrections to these approximate formulas are given in Table II.