摘要: The correlations observed in bright low-mass X-ray binaries between colours and rapid variability (including quasi-periodic oscillations) indicate the existence of two types sources, Z atoll each showing several different modes behaviour or “states”. intensity, spectrum, optical, UV radio emission burst properties all correlate with this phenomenological classification, but intensity does so only approximately, that it is not strictly proportional to accretion rate. observational evidence underlying classification summarized, a tentative interpretation terms differences rate magnetic field strength neutron stars given discussed within framework binary evolution, relation sources other LMXB considered.