1. Dynamical Timescales for High-Mass X-Ray Binaries

The temporal behavior depends on several characteristic times. The most obvious is the rotation period of the neutron star which gives rise to the observed coherent pulsations. The orbital period is another. Some X-ray binaries such as the LMXB pulsar Her X-1 exhibit third periods due to a precessing accretion disk (e.g. White et al. (1995) and references therein). The Keplerian rotation period of the inner accretion disk is another observationally important timescale. The beat period between this and the pulsar rotation period may be manifested as quasi-periodic modulations of the light curve (see Section 5.5). The dynamical timescales in the accretion column close to the neutron star are $\sim$ 0.1 ms (van der Klis (1997)).