Black hole-like hysteresis and accretion states in neutron star low mass X-ray binaries

Understand

We have systematically studied a large sample of the neutron star low mass X-ray binaries (LMXBs) monitored by the Rossi X-ray Timing Explorer (50 sources; 10000+ observations).

• We find that the hysteresis patterns between Compton dominated and thermal dominated states, typically observed in black hole LMXBs, are also common in neutron star systems.
• These patterns, which also sample intermediate states, are found when looking at the evolution of both X-ray colour and fast variability of ten systems accreting below ~ 30 % of the Eddington Luminosity.
• We show that hysteresis does not require large changes in luminosity and it is the natural form that state transitions take at these luminosities.