The X-ray spectrum of Cyg X-2

被引:44
作者
Done, C
Zycki, PT
Smith, DA
机构
[1] Univ Durham, Dept Phys, Durham DH1 3LE, England
[2] Nicholas Copernicus Astron Ctr, PL-00716 Warsaw, Poland
[3] Univ Maryland, College Pk, MD 20742 USA
关键词
accretion; accretion discs; radiation mechanisms : thermal; binaries : close; stars : individual : Cyg X-2; stars : neutron; X-rays : stars;
D O I
10.1046/j.1365-8711.2002.05195.x
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
The spectra of disc accreting neutron stars generally show complex curvature, and individual components from the disc, boundary layer and neutron star surface cannot be uniquely identified. Here we show that much of the confusion over the spectral form derives from inadequate approximations for Comptonization and for the iron line. There is an intrinsic low-energy cut-off in Comptonized spectra at the seed photon energy. It is very important to model this correctly in neutron star systems as these have expected seed photon temperatures (from either the neutron star surface, inner disc or self-absorbed cyclotron) of approximate to1 keV, clearly within the observed X-ray energy band. There is also reflected continuum emission which must accompany the observed iron line, which distorts the higher energy spectrum. We illustrate these points by a reanalysis of the Ginga spectra of Cyg X-2 at all points along its Z track, and show that the spectrum can be well fitted by models in which the low-energy spectrum is dominated by the disc, while the higher energy spectrum is dominated by Comptonized emission from the boundary layer, together with its reflected spectrum from a relativistically smeared, ionized disc.
引用
收藏
页码:453 / 462
页数:10
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