ASCA Observations of GX 354−0 and KS 1731−260

Abstract

We report on ASCA observations of the low-mass X-ray binaries GX 354 - 0 and KS 1731 - 260. The spectrum of GX 354 - 0 is best described as a power law or a Comptonized spectrum with τ ∼ 5 and kT ∼ 8 keV and a residual at ∼ 6.5 keV. The residual may be a disk reflection or a Compton-broadened Gaussian line from the hot inner advection-dominated accretion flow-like coronal region. The absorption column density to the source is 2.9 × 1022 cm-2. No soft thermal component was detected. The spectrum from KS 1731 - 260 is softer, and it is best fit with a two-component model with a column density of 1.1 × 1022 cm-2. The likely interpretation is emission from a Comptonizing cloud with an optical depth τ > 12 and either a neutron star or a disk blackbody emission. We discuss the likely location of the Comptonizing cloud for both sources within the context of several proposed emission models.