Optical spectroscopy of GX 339−4 during the high–soft and low–hard states – II. Line ionization and emission region |
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| Authors: | Kinwah Wu Roberto Soria Richard W Hunstead Helen M Johnston |
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| Institution: | Research Centre for Theoretical Astrophysics, School of Physics, University of Sydney, NSW 2006, Australia;Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking RH5 6NT;Astrophysics Department, School of Physics, University of Sydney, NSW 2006, Australia;Anglo-Australian Observatory, PO Box 196, Epping, NSW 1710, Australia |
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| Abstract: | We have carried out observations of the X-ray transient GX 339?4 during its high–soft and low–hard X-ray spectral states. Our high-resolution spectroscopic observation in 1999 April suggests that the H α line has a single-peaked profile in the low–hard state as speculated in our previous paper. The He ii λ 4686 line, however, has a double-peaked profile in both the high–soft and low–hard states. This suggests that the line-emission mechanism is different in the two states. Our interpretation is that double-peaked lines are emitted from a temperature-inversion layer on the accretion disc surface when it is irradiatively heated by soft X-rays. Single-peaked lines may be emitted from outflow/wind matter driven by hard X-ray heating. We have constructed a simple plane-parallel model and we use it to illustrate that a temperature-inversion layer can be formed at the disc surface under X-ray illumination. We also discuss the conditions required for the formation of temperature inversion and line emission. Based on the velocity separations measured for the double-peaked lines in the high–soft state, we propose that GX 339?4 is a low-inclination binary system. The orbital inclination is about 15° if the orbital period is 14.8 h. |
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| Keywords: | accretion accretion discs black hole physics binaries: spectroscopic stars: individual: GX 339?4 |
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