Discovery of complex narrow X-ray absorption features from the low-mass X-ray binary GX13+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 K α and K β lines of He- and H-like iron (Fe xxv and Fe xxvi ) and H-like calcium (Ca xx ) K α . Only the Fe xxvi K α line has been previously observed from GX 13+1. Due to the closeness in energy the Fe xxv and Fe xxvi K β features may also be ascribed to Ni xxvii and Ni xxviii K α , respectively. We also find evidence for the presence of a deep ( τ ∼ 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 K α 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.