The X-ray and extreme-ultraviolet flux evolution of SS Cygni throughout outburst
The X-ray and extreme-ultraviolet flux evolution of SS Cygni throughout outburst
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DOI：
10.1046/j.1365-8711.2003.06936.x
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发表时间：
2003-06
影响因子：
4.8
通讯作者：
P. Wheatley;C. Mauche;J. Mattei
中科院分区：
文献类型：
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作者：
P. Wheatley;C. Mauche;J. Mattei
我们展示了任何矮新星爆发的最完整的多波长覆盖：同时光学，极紫外探测器和罗西x射线定时探测器在一个狭窄的不对称爆发中对SS Cygni的观测。我们的数据表明，高能爆发开始于x射线波段，在光学上升开始后0.9-1.4 d，在极紫外上升开始前0.6 d。在极紫外通量上升之前，x射线通量突然下降，这支持了这两种成分都出现在吸积盘和白矮星表面之间的边界层的观点。x射线通量的早期上升表明，爆发热波的传播时间可能被高估了。x射线和极紫外主导发射之间的转变伴随着x射线通量的强烈变化，其时间尺度为分钟。正如Mauche和Robinson详细描述的那样，矮新星的振荡在极紫外爆发中被探测到，但我们发现它们在x射线光曲线中不存在。x射线和极紫外光度表明，吸积速率在静止时为3 × 1015 g s - 1，边界层变厚时为1 × 1016 g s - 1，爆发峰时为~ 1018 g s - 1。静止吸积速率比标准吸积盘不稳定性模型预测的高2.5个数量级，我们认为这可能是因为SS Cyg的内部吸积盘处于永久爆发状态。
We present the most complete multiwavelength coverage of any dwarf nova outburst: simultaneous optical, Extreme Ultraviolet Explorer and Rossi X-ray Timing Explorer observations of SS Cygni throughout a narrow asymmetric outburst. Our data show that the high-energy outburst begins in the X-ray waveband 0.9–1.4 d after the beginning of the optical rise and 0.6 d before the extreme-ultraviolet rise. The X-ray flux drops suddenly, immediately before the extreme-ultraviolet flux rise, supporting the view that both components arise in the boundary layer between the accretion disc and white dwarf surface. The early rise of the X-ray flux shows that the propagation time of the outburst heating wave may have been previously overestimated. The transitions between X-ray and extreme-ultraviolet dominated emission are accompanied by intense variability in the X-ray flux, with time-scales of minutes. As detailed by Mauche & Robinson, dwarf nova oscillations are detected throughout the extreme-ultraviolet outburst, but we find they are absent from the X-ray light curve. X-ray and extreme-ultraviolet luminosities imply accretion rates of 3 × 1015 g s−1 in quiescence, 1 × 1016 g s−1 when the boundary layer becomes optically thick, and ∼1018 g s−1 at the peak of the outburst. The quiescent accretion rate is two and a half orders of magnitude higher than predicted by the standard disc instability model, and we suggest this may be because the inner accretion disc in SS Cyg is in a permanent outburst state.