Chandra High‐Resolution Spectroscopy of the Absorption‐Line Features in the Low‐Mass X‐Ray Binary GX 13+1

Abstract

We present the results of high-resolution spectroscopy of absorption-line features of highly ionized ions in the X-ray spectra of GX 13+1 with the Chandra HETGS. We have resolved Ka absorption lines of hydrogen-like Fe, Mn, Cr, Ca, Ar, S, Si, and Mg ions and helium-like Fe ions. Applying the Voigt profile to these spectral features, we find that the plasma responsible for the absorption lines has a significant blueshift of 460 ±70 km s-1, indicating an outflow velocity of ≈400 km s-1 corrected for the proper motion, with a line-of-sight velocity dispersion of 490 -140+110 km s-1. The plasma is photoionized with an ionization parameter of log ξ ≃ 4.1-4.7. The inferred mass outflow rate is 0.7 × 1018 g s-1 or higher, comparable to the mass accretion rate (1018 g s-1) estimated from the continuum spectrum. This indicates that the mass outflow plays a significant role to determine the whole dynamics of the accretion disk. We consider a simplified radiation-driven disk wind model for the origin of the outflow. Our observations are explained by the wind originating from radii of ∼1010-1011 cm with a density ≲1013 cm-3.