2013MNRAS.433..746C

Eight years of optical photometry from OGLE-III are presented of the optical counterpart to the high-mass X-ray binary system, SMC X-1. The optical data provide the best view to date of the modulation of the light from the system at the binary period of 3.9d. In addition, it is shown for the first time that the light is also modulated at the superorbital period - a period associated with the precessing of a warped accretion disc around the neutron star partner. The implications for the sources of the various components of the optical light in this system are discussed.