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

Free access article

Issue		A&A Volume 385, Number 3, April III 2002


Page(s)		940 - 946
Section		Formation, structure and evolution of stars
DOI		http://dx.doi.org/10.1051/0004-6361:20020192

A&A 385, 940-946 (2002)
DOI: 10.1051/0004-6361:20020192

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, 20133 Milano, Italy
² Astrophysics Division, Research and Scientific Support Department of ESA, ESTEC, Postbus 299, 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 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 $\alpha$ and K $\beta$ lines of He- and H-like iron (Fe XXV and Fe XXVI) and H-like calcium (Ca XX) K $\alpha$ . Only the Fe XXVI K $\alpha$ line has been previously observed from GX 13+1. Due to the closeness in energy the Fe XXV and Fe XXVI K $\beta$ features may also be ascribed to Ni XXVII and Ni XXVIII K $\alpha$ , respectively. We also find evidence for the presence of a deep ( $\tau \sim 0.2$ ) 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 $\alpha$ 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: GX 13+1 -- stars: neutron -- X-rays: general

Offprint request: L. Sidoli, sidoli@ifctr.mi.cnr.it

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