Spectral state transitions in Aquila X-1: evidence for 'propeller' effects

摘要

Aquila X-1 is a soft X-ray transient source and emits type I X-ray bursts. A spectral state transition was observed with RXTE during its outburst decay in 1997 February and March. Its 10-30 keV and 5-10 keV count rate ratio increased suddenly when its luminosity was between 4 and 12 X 10~35 ergs s~-1, assuming a 2.5 kpc distance. Spectral fitting with a model composed of a blackbody and a power-law component showed that its blackbody component decreased and that the power-law component became much harder significantly and si- multaneously. We interpret this transition to be caused by the centrifugal barrier, more commonly known as the "propeller" effect.