Luminosity-related changes of the energy spectrum of X 1608-522.

The low-mass binary X-ray source X1608-522 was observed from Tenma over a wide range of luminosity. The spectrum showed a large and gradual change from a thermal type at high luminosities to a power-law type as the luminosity went down. This demonstrates that the spectral shape depends on the accretion rate and does not represent distinct characteristics of the individual sources. A two-component model spectrum consisting of a Comptonized black-body component and another softer component (expected for an optically thick accretion disk) can explain all the observed spectra consistently.