Gravitational wave observations of galactic intermediate-mass black hole binaries with DECIGO Path Finder

Abstract

DECIGO Path Finder (DPF) is a space-borne gravitational wave (GW) detector with sensitivity in the frequency band 0.1--100Hz. As a first step mission to DECIGO, it is aiming for launching in 2016--2017. Although its main objective is to demonstrate technology for GW observation in space, DPF still has a chance of detecting GW signals and performing astrophysical observations. With an observable range up to 50 kpc, its main targets are GW signals from galactic intermediate mass black hole (IMBH) binaries. By using inspiral-merger-ringdown phenomenological waveforms, we perform both pattern-averaged analysis and Monte Carlo simulations including the effect of detector motion to find that the masses and (effective) spins of the IMBHs could be determined with errors of a few percent, should the signals be detected. Since GW signals from IMBH binaries with masses above $10^4 M_\odot$ cannot be detected by ground-based detectors, these objects can be unique sources for DPF. If the inspiral signal of a $10^3M_\odot$ IMBH binary is detected with DPF, it can give alert to the ringdown signal for the ground-based detectors $10^2$--$10^3$s before coalescence. We also estimate the possible bound on the graviton Compton wavelength from a possible IMBH binary in $ω$ Centauri. We obtain a slightly weaker constraint than the solar system experiment and an about 2 orders of magnitude stronger constraint than the one from binary pulsar tests. Unfortunately, the detection rate of IMBH binaries is rather small.