Volume 526, February 2011
|Number of page(s)||10|
|Section||Stellar structure and evolution|
|Published online||22 December 2010|
Detecting emission lines with XMM-Newton in 4U 1538–52
Department of Physics, Systems Engineering and Sign Theory, University of
2 University Institute of Physics Applied to Sciences and Technologies, University of Alicante, 03080 Alicante, Spain
3 Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK
Received: 26 February 2010
Accepted: 7 November 2010
Context. The properties of the X-ray emission lines are a fundamental tool for studying the nature of the matter surrounding the neutron star and the phenomena that produce these lines.
Aims. The aim of this work is to analyse the X-ray spectrum of 4U 1538−52 obtained by the XMM-Newton observatory and to look for the presence of diagnostic lines in the energy range 0.3−11.5 keV.
Methods. We used a 54 ks PN & MOS/XMM-Newton observation of the high-mass X-ray binary 4U 1538−52 covering the orbital phase between 0.75 to 1.00 (the eclipse ingress). We modelled the 0.3−11.5 keV continuum emission with three absorbed power laws and looked for the emission lines.
Results. We found previously unreported recombination lines in this system at ~2.4 keV, ~1.9 keV, and ~1.3 keV, which is consistent with the presence of highly ionized states of S XV Heα, Si XIII Heα, and either Mg Kα or Mg XI Heα. On the other hand, in spectra that are both out of eclipse and in eclipse, we detect a fluorescence iron emission line at 6.4 keV, which is resolved into two components: a narrow (σ ≤ 10 eV) fluorescence Fe Kα line plus one hot line from highly photoionized Fe XXV.
Conclusions. The detection of new recombination lines during eclipse ingress in 4U 1538−52 indicates that there is an extended ionized region surrounding the neutron star.
Key words: X-rays: binaries / pulsars: individual: 4U 1538−52
© ESO, 2010
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