LOW STATE PROPERTIES OF THE LOW-MASS X-RAY BINARY-X1608-522 OBSERVED WITH GINGA

The low-mass X-ray binary X1608-522 was observed with Ginga on three o ccasions from 1989 to 1991. The source was in the low state throughout the observations. The energy spectrum in the energy range of 2-60 keV can be approximated by a power-law function with a broad absorption-l ike structure. The structure can be represented either by partial abso rption or by a reflection of the power-law spectrum. The ionization de gree of the absorbing/reflecting medium increases when the source lumi nosity increases by a factor of about three, while the percentage of t he absorbed/reflected component relative to the total intensity decrea ses. The power spectrum is characterized by a flat top below a certain frequency, while it decreases approximately as 1/f above that frequen cy. The turn-over frequency varies according to the source luminosity, and is in a range 0.2 to 1 Hz. Additional structures, which can be re presented by a broad Lorentzian peak, also exist in the power spectrum . The physical state of the accretion disk is discussed in conjunction with the low state of black-hole candidates.