Discovery of complex narrow X-ray absorption features from the low-mass X-ray binary GX 13+1 with XMM-Newton

We report the detection of a complex of narrow X-ray absorption features from the low-mass X-ray binary GX 13+1 during 3 XMM-Newton observations in 2000 March and April. The features are consistent with being due to resonant scattering of the Kalpha and Kbeta lines of He- and H-like iron (Fe XXV and Fe XXVI) and H-like calcium (Ca XX) Kalpha . Only the Fe XXVI Kalpha line has been previously observed from GX 13+1. Due to the closeness in energy the Fe XXV and Fe XXVI Kbeta features may also be ascribed to Ni XXVII and Ni XXVIII Kalpha , respectively. We also find evidence for the presence of a deep (tau ~ 0.2) Fe XXV absorption edge at 8.83 keV. The fits also require the presence of a broad emission feature whose energy and width are poorly determined, partly due to the presence of the deep Fe Kalpha features which severely cut into the feature and partly due to fit differences when using different XMM-Newton instruments. The equivalent widths of the lines do not show any obvious variation on a timescale of a few days suggesting that the absorbing material is a stable feature of the system and present during a range of orbital phases.