NEW FEATURES OF THE X-RAY DIP SOURCE 1755-338

Abstract

The X-ray dip source 1755-338 was observed with Ginga and simultaneously with Ginga and ROSAT in 1991. The source was in the ''high'' luminosity state during the observation in 1990, similar to the EXOSAT observation. Regularly spaced dips and no apparent low-energy absorption during these dips are confirmed. During the observation in 1991, the source was in the ''low'' luminosity state with the flux (1-37 keV) less than 35% of the ''high'' state nondip level. The spectrum observed in this ''low'' state is much harder than that in the ''high'' state. Also, an iron emission line centered around 6.7 keV is found in the ''low'' state. The data imply that the accreting matter in this system might have the cosmic abundance, contrary to the earlier suggestion that the heavy-element abundances in 1755-338 are extremely low. The equivalent neutral hydrogen column density is similar to 4 x 10(21) cm(-2) in the low state, as deduced from the combined data of ROSAT and Ginga.