Discovery of an iron K absorption line in the low-mass X-ray binary GX 13+1

We report the discovery of an iron K absorption-line feature with ASCA in t he spectra of the low-mass X-ray binary GX 13 + 1. The absorption line is d etected at 7.0 keV with an equivalent width of 35 +/- 8 eV, which is attrib uted to resonant scattering of the K alpha line from Fe XXVI ions in the li ne of sight whose column density is larger than similar to 10(18) cm(-2). T he detection of such a spectral feature from a neutron star binary rules ou t the hypothesis that it is unique to the Galactic superluminal jet sources . From the similarity of the line parameters to those of the superluminal s ources, we infer that we view the X-ray emission through a highly ionized p lasma in outer parts of the accretion disk with a relatively high inclinati on angle. This picture is consistent with the universal presence of such pl asmas in X-ray binaries accreting through disks.