A relativistically smeared spectrum in the neutron star X-ray binary 4U 1705-44: looking at the inner accretion disc with X-ray spectroscopy

Antonino D'Ai', Rosario Iaria, Tiziana Di Salvo, Natale Robba, Riggio, Andrea Santangelo, Piraino, Burderi, Karas, Matt, Papitto, Dovčiak

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58 Citations (Scopus)

Abstract

Iron emission lines at 6.4-6.97 keV, identified with fluorescent Kα transitions, are among the strongest discrete features in the X-ray band. These are therefore one of the most powerful probes to infer the properties of the plasma in the innermost part of the accretion disc around a compact object. In this paper, we present a recent XMM-Newton observation of the X-ray burster 4U 1705-44, where we clearly detect a relativistically smeared iron line at about 6.7 keV, testifying with high statistical significance that the line profile is distorted by high-velocity motion in the accretion disc. As expected from disc reflection models, we also find a significant absorption edge at about 8.3 keV; this feature appears to be smeared, and is compatible with being produced in the same region where the iron line is produced. From the line profile, we derive the physical parameters of the inner accretion disc with large precision. The line is identified with the Kα transition of highly ionized iron, FeXXV, the inner disc radius is Rin = 14 +/- 2 Rg (where Rg is the Gravitational radius, GM/c2), the emissivity dependence from the disc radius is r-2.27+/-0.08, the inclination angle with respect to the line of sight is i = 39° +/- 1°. Finally, the XMM-Newton spectrum shows evidences of other low-energy emission lines, which again appear broad and their profiles are compatible with being produced in the same region where the iron line is produced.
Original languageEnglish
Pages (from-to)2022-2027
Number of pages5
JournalMonthly Notices of the Royal Astronomical Society
Volume398
Publication statusPublished - 2009

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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