Discovery of complex narrow X-ray absorption features from the low-mass X-ray binary GX13+1.pdfVIP

a r X i v : a s t r o - p h / 0 2 0 2 0 7 7 v 1 4 F e b 2 0 0 2 Astronomy Astrophysics manuscript no. (will be inserted by hand later) Discovery of complex narrow X–ray absorption features from the low-mass X–ray binary GX 13+1 with XMM-Newton L. Sidoli1, A. N. Parmar2, T. Oosterbroek2, and D. Lumb2 1 Istituto di Fisica Cosmica “G. Occhialini”, CNR, via Bassini 15, I-20133 Milano, Italy 2 Astrophysics Division, Research and Scientific Support Department of ESA, ESTEC, Postbus 299, NL-2200 AG Noordwijk, The Netherlands Received 19 December 2001 / Accepted: 31 January 2002 Abstract. We report the detection of a complex of narrow X–ray absorption features from the low-mass X–ray binary GX13+1 during 3 XMM-Newton observations in 2000 March and April. The features are consistent with being due to resonant scattering of the Kα and Kβ lines of He- and H-like iron (Fexxv and Fexxvi) and H-like calcium (Caxx) Kα. Only the Fexxvi Kα line has been previously observed from GX13+1. Due to the closeness in energy the Fexxv and Fexxvi Kβ features may also be ascribed to Nixxvii and Nixxviii Kα, 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 Kα 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. Key words. Accretion, accretion disks – Stars: individual: GX13+1 – Stars: neutron – X–rays: general 1. Introduction The bright and persistent low-mass X–ray binary (LMXRB) GX13+1 (4U1811–17) is an X–ray burst source (Fleischman 1985; Matsuba 1995) with radio (Grindlay Seaquist 1986) and inf