I 型 X 射线暴 (热核暴) 是在 X 射线波段强度突然增加，并且亮于暴前辐射 的∼ 10−100 倍的高能现象；一般认为是在低质量 X 射线双星系统中吸积中子 星表面上吸积物质的不稳定燃烧引起的。一般可以利用I型暴研究中子星表面的 吸积物质成分及密度、温度、吸积率，还对研究中子星表面的辐射特征和系统的 吸积环境有重要意义。由于热核暴发生在中子星的硬表面，所以可认证低质量X 射线双星系统的致密星为中子星。达到爱丁顿光度的光球扩展暴还可以作为测 量距离的标准烛光。 典型热核暴的光变曲线是单峰结构，呈现出快速上升，幂指数衰减的形态 (FRED)。随着观测样本的增加，出现了一类在X射线波段光变曲线和流量演化 都显示多峰结构的热核暴。这类双峰暴比较稀有，且其物理起源一直是一个谜 题。基于对现有出现多峰暴的暴源的调研，我们发现源4U1636−53的双峰暴暴 发相对活跃。 我们利用 RXTE 卫星在源 4U 1636−53 中 336 个 I 型暴中找到了 16 个多峰 暴。我们发现，其中有 14 个双峰暴，1 个三峰暴，1 个四峰暴。此四峰暴从来没 被先前的工作报道过。这 16 个多峰暴在X射线波段的光变曲线和流量演化中都 显示出双峰结构。我们发现，大多数多峰暴出现在双色图中的转换态。我们发现 在第二个峰值流量和两峰值时间间隔之间存在反相关关系。我们还发现在 14 个 双峰暴样本中，峰值流量比值与暴前能谱热成分的温度是相关的。这个结果表明 暴的双峰结构可能受吸积盘的吸积率增加的影响，或者受中子星温度的影响。
其他摘要
Thermonuclear (type-I) X-ray bursts show a sudden increase in X-ray intensity, becoming ~10-100 times brighter than the persistent level, triggered by unstable ignition of accreted fuel on the surface of an accreting neutron star (NS) in low mass X-ray binaries (LMXB).We can use the
type-I X-ray bursts to investigate the accretion composition on the
Neutron Star or other characters, including density, temperature,
accretion rate. And it is important to probe the radiation and
accretion environment on the surface of the Neutron Star. The type-I
X-ray bursts can identify the hard surface of the Neutron Star. The
photospheric radius expansion which reach the Eddington luminosity
can calculate the distance as standard candles.In a typical X-ray burst, the light curve shows a single-peaked
profile with a fast rise (∼ 1 − 5 s) and an exponential decay
(FRED). There is a kind of burst which is a rarity and has
double-peaked structure both in X-ray light curve and bolometric
flux. This is a question about the origin of the double-peaked X-ray
burst. Based on the research of bursters which have multi-peaked
bursts, we find that 4U 1636−53 has larger multi-peaked X-ray burst
than others.We study 336 type-I X-ray bursts in LMXB 4U 1636−53 with RXTE
and discover 16 multi-peaked bursts. We find 14 double-peaked bursts,
one triple-peaked burst and one quadruple-peaked burst which was not
reported in previous work. All of these 16 bursts show a multi-peaked
structure not only in the X-ray light curves but also in the
bolometric light curves. Most of the multi-peaked bursts appear in
observations during the transition from the hard to the soft state in
the colour-colour diagram. We find an anti-correlation between the
second peak flux and the separation time between two peaks. We also
find that in the double-peaked bursts the peak-flux ratio and the
temperature of the thermal component in the pre-burst spectra are
correlated. This indicates that the double-peaked structure in the
light curve of the bursts may be affected by enhanced accretion rate
in disk, or increased temperature of the neutron star.
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