【作者】 李亮；

【导师】 梁恩维；

【作者基本信息】 广西大学 ， 理论物理， 2012， 硕士

【摘要】 我们总结了伽玛暴和其光学余辉观测和目前我们对各种光学辐射成分的分析结果。我们大范围的从文献里收集光学数据,获得了146个好的伽玛暴光学光变曲线样本并且用组合的分段幂律函数去拟合可能有着不同物理起源的各种辐射成分。我们的结果用一张综合的光学光变曲线来总结。基于我们系统的分析结果,我们着重分析了与长时标中心引擎活动相关的耀发和早期光学缓慢衰减两个辐射成分。从19个伽玛暴中获得了24个光学耀发。耀发的峰值从暴后触发数十秒到几天,晚期的耀发呈现越宽越暗的趋势,幂律关联指数为-1.15±0.15。观测到的伽玛暴光学耀发的比例远远小于X射线耀发比例,并且仅仅对应有4个暴也观测到X射线耀发。39个暴中发现有光学缓慢衰减。拐折时间从暴后触发的几十秒到几天的时间量级,典型的时标是10^4秒。拐折光度与拐折时间以幂律指数-0.78呈现一个反相关性。光学缓慢衰减成分比例与X射线波段的缓慢衰减成分比例相当。X射线和光学拐折通常是多色的。我们认为光学耀发与中心引擎不稳定的行为相关联,缓慢衰减成分可能由于冲击波的能量注入,可能与长时标的自旋减慢的中心引擎或者冲击波的耀发物质的堆积相关联。清晰的早期余辉鼓包成分,可能由于伽玛暴的火球通过星际介质减速所产生,观测到有45个样本。早期余辉鼓包峰值呈现越晚越宽和越暗的关系。峰值光度与伽玛暴瞬时各向同性能之间呈现一个紧密的关系。峰值过后的衰减斜率是很好的与标准的火球模型预言的相一致,但是上升的阶段在均匀星际介质和星风环境介质两种介质环境下是与期望是不相一致的,我们从上升斜率推断伽玛暴的周围密度轮廓发现n∝r-k,K=0.5～1.5。然后我们在一次基于密度形式基础上重新估算了伽玛暴的初始洛伦茨因子以及它与暴本身各向同性能之间的关联。我们的样本中从30个伽玛暴中观测到有晚期的光学重新增亮行为。重新增亮鼓包的上升和下降斜率的分布是与早期余辉鼓包是很一致的,但是峰值光度是与伽玛暴各向同性能之间没有关联。这些结果支持了重新增亮鼓包可能是另一个喷流成分的贡献。在X波段也同时观测到少量的几个暴对应有重新增量鼓包现象,像100901A,060906,080913等。这意味着两个波段的辐射应该来自与相同的喷流成分。更多还原

【Abstract】 We summarize the observations of gamma-ray bursts and their optical afterglows and present our analysis results on various optical emission components of this phenomenon.By extensively searching from literature, we got well-sampled optical lightcurves of146gamma-ray bursts (GRBs) and fitted these lightcurves with the superposition of multiple broken power law functions to identify various emission components that may have distinct physical origins. We summarize the results in a "synthetic" optical lightcurve. Based on our statistical analysis results, we found that optical flares and an early optical shallow-decay component are likely related to a long-term central engine activity. Twenty-four optical flares are obtained from19GRBs. The flares peak at from tens of seconds to several days post the GRB trigger, and later flares tend to be wider and dimmer, following a power-law relation with an index of-1.15±0.15. The fraction of GRBs with detected optical flares is much smaller than that of X-ray flares. Associated X-ray flares are observed for4optical flares, and the optical flares usually lag behind the corresponding X-ray flares. An optical shallow decay segment is observed in39GRBs. Their break times range from tens of seconds to several days post the GRB trigger, with a typical value of104seconds. The break luminosity is anti-correlated to the break time with a power-law index of-0.78, similar to that derived from X-ray flares. The detection fraction of the optical shallow decay component is comparable to that in the X-ray band. The X-ray and optical breaks are usually chromatic, but a tentative correlation is found. We suggest that the optical flares are also related to the erratic behavior of the central engine and the shallow decay component, on the other hand, is likely due to energy injection into the blastwave, possibly related to a long-lasting spinning-down central engine or piling up of flare materials onto the blastwave.Clear afterglow onset humps, which may be due to the decelerateion of the GRB fireball by the embient medium, are observed in45GRBs in our sample. An onset hump peaks ayt later tends to be wider and dimmer, and the peak luminosity is tight correlated with the isotropic prompt gamma-ray energy. The decay slopes after the peak time of the humps are well consistent with the standard fireball, but the slopes of the rising phase are inconsistent with the expectation in both inter stelar medium (ISM) and wind medium. We infer the density profile surrounding GRBs from the rising slopes and find that nocr"k, where k=0.5-1.5. We then estimate the initial Lorentz factors of the GRB fireball based with these density profiles and re-visit the correlation between the isotropic gamma-ray energy the Lorentz factor.Late optical rebrightening is observed for30GRBs in our sample. The distributions of the rising and decaying slopes of the rebrightening bumps are well consistent with that of the onset bumps. A re-brightening hump peaks at later also tends to be wider and dimmer, but the peak luminosity is not correlated with the isotropic prompt gamma-ray energy. These results might suggest that the late rebrightening could be contributed by another jet component. Associated X-ray re-brightening bump is also detected in a few GRBs, such as100901A,060906, and080913. This indicates that the emission in the two energy bands should be from the same jet component.更多还原