  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 $\omega$ 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.

Cosmology and Nongalactic Astrophysics;General Relativity and Quantum Cosmology