Timing stability of millisecond pulsars and prospects for
  gravitational-wave detection
  Analysis of high-precision timing observations of an array of approx. 20
millisecond pulsars (a so-called "timing array") may ultimately result in the
detection of a stochastic gravitational-wave background. The feasibility of
such a detection and the required duration of this type of experiment are
determined by the achievable rms of the timing residuals and the timing
stability of the pulsars involved. We present results of the first long-term,
high-precision timing campaign on a large sample of millisecond pulsars used in
gravitational-wave detection projects. We show that the timing residuals of
most pulsars in our sample do not contain significant low-frequency noise that
could limit the use of these pulsars for decade-long gravitational-wave
detection efforts. For our most precisely timed pulsars, intrinsic
instabilities of the pulsars or the observing system are shown to contribute to
timing irregularities on a five-year timescale below the 100 ns level. Based on
those results, realistic sensitivity curves for planned and ongoing timing
array efforts are determined. We conclude that prospects for detection of a
gravitational-wave background through pulsar timing array efforts within five
years to a decade are good.
