The light curves of soft X‐ray transients
The light curves of soft X‐ray transients
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DOI：
10.1046/j.1365-8711.1998.01295.x
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发表时间：
1988
影响因子：
4.8
通讯作者：
A. King;H. Ritter
中科院分区：
文献类型：
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作者：
A. King;H. Ritter
我们发现，软X射线瞬态（SXTs）的光变曲线自然地遵循光盘不稳定性图片，适应考虑到辐射的中央X射线源在爆发。辐射阻止盘返回到冷却状态，直到中心吸积大大减少。这只发生在大部分圆盘质量已经被中心物体吸积之后，在粘性时间尺度上，自然地解释了爆发在比矮新星更长的时间尺度（τ20-40 d）上的指数衰减，而不需要操纵粘性参数α。大部分的盘质量的吸积在爆发解释了长得多的复发时间的SXTs相比，矮新星。这张照片也解释了在每次爆发开始后约50-75 d在SXT光变曲线中看到的第二个最大值，因为中心照射触发了外盘的热不稳定性，在一个粘性时间后增加了中心吸积率。X射线爆发衰减常数τ平均应随轨道周期增加而增加，但当轨道周期大于1天时，τ会在约40 d处达到饱和。测辐射热光变曲线在后期（几倍于τ）应显示线性衰减而不是指数衰减。长周期系统的爆发应该完全处于线性衰变状态，正如GRO J1744−28所观察到的那样。紫外线和可见光的光变曲线应该类似于X射线，但衰减时间比X射线长2-4倍。
We show that the light curves of soft X-ray transients (SXTs) follow naturally from the disc instability picture, adapted to take account of irradiation by the central X-ray source during the outburst. Irradiation prevents the disc from returning to the cool state until central accretion is greatly reduced. This happens only after most of the disc mass has been accreted by the central object, on a viscous time-scale, accounting naturally for the exponential decay of the outburst on a far longer time-scale (τ20–40 d) than seen in dwarf novae, without any need to manipulate the viscosity parameter α. The accretion of most of the disc mass in outburst explains the much longer recurrence time of SXTs compared with dwarf novae. This picture also suggests an explanation of the secondary maximum seen in SXT light curves about 50–75 d after the start of each outburst, since central irradiation triggers the thermal instability of the outer disc, adding to the central accretion rate one viscous time later. The X-ray outburst decay constant τ should on average increase with orbital period, but saturate at a roughly constant value ∼40 d for orbital periods longer than about a day. The bolometric light curve should show a linear rather than an exponential decay at late times (a few times τ). Outbursts of long-period systems should be entirely in the linear decay regime, as is observed in GRO J1744−28. UV and optical light curves should resemble the X-rays but have decay time-scales up to 2–4 times longer.