逆康普顿散射对γ暴余辉的影响

γ暴余辉的发现是γ暴研究史上的一个重大突破,火球模型几乎可以较好地解释γ暴余辉的观测特性。但在标准的火球模型中,通常只考虑电子的同步加速辐射,没有考虑电子逆康普顿散射的贡献。这里我们详细计算了逆康普顿散射对γ暴余辉的影响,发现在一定的条件下,逆康普顿散射的影响是很重要的,它可以显著地改变辐射能谱,进而改变γ暴余辉的光变特性。     

脉冲星参数的取值对γ暴火球余辉的影响

用中心有脉冲星的γ射线暴的火球模型计算出GRB970228和GRB000301c两个γ射线暴的余辉辐射流，计算结果与观测结果相比较，符合的很好，解释了GRB970228和GRB000301c光学R波段余辉的光变曲线带‘拐折’的特征，讨论了中心脉冲星参数的取值对余辉的光曲线起的重要作用。     

γ暴的能源和环境

评论了γ暴能源的某些机制，比如：巨超新星爆发，磁白短星的塌缩，磁星的诞生，中子星的相变等，重点评述了中心星脉冲星的以胆注入周围环境对γ暴余辉的影响，讨论了将来在γ暴领域的可能研究。     

具平缓电子能谱的伽玛射线暴的解析光变曲线

在标准的伽玛暴余辉模型中,电子通过费米一级加速后形成单幂律能谱分布dn/dγe∝γe-p(p≈2.3),但在某些伽玛暴事件中观测到了平缓的电子能谱分布(即p＜2).在单幂律谱和分段幂律谱两种情况下,分别给出了具有平缓电子能谱的伽玛暴余辉的解析光变曲线,并以GRB 060908为例进行了讨论.同时提出了伽玛暴低能谱危机的...     

等时面与γ射线暴余辉

在γ射线暴（ 简称γ暴） 的火球模型下,γ暴余辉存在等时面,面上发射的光子会同时被观测到．通过对等时面积分来计算辐射流量Ｆν（ｔ） ,结果表明等时面的引入对峰值以及峰值前后流量随观测者时间的变化关系有明显的影响     

亮暗暴的早期X射线研究

研究亮暴和暗暴的X射线余辉,发现它们的X射线和γ流量的分布基本上相同。即:从统计学的角度上讲,亮暴和暗暴没有本质不同,它们的中心机制应该是相同的,暗暴的形成应该是由环境原因引起的。     

Swift时代伽玛射线暴及其余辉的多波段研究

<正>伽玛射线暴(简称伽玛暴)是一种来自太空任意方向的伽玛射线(ε_γ≈0.1～1 MeV)脉冲式辐射现象,暴后一般伴随有长时间的低频余辉辐射.为了对早期余辉乃至瞬时辐射进行多波段观测,美国国家航空航天局(NASA)于2004年11月发射了专门用于伽玛暴研究的Swift卫星.该卫星工作以来,以其快速响应与精确定位的能力和多波段观测的手段取得了一系列令人瞩目的成就(本文第1章将对     

Gamma暴余辉的相对论流体动力学演化和光变曲线

本文首先对Gamma暴的观测特性和物理过程作了简要的介绍，而后，对火球模型的相对论流体动力学机制和同步加速辐射机制作了论述。主要工作是：具体研究火球所抛出壳层的相对论流体动力学演化，应用同步加速辐射机制，通过由共动坐标系到实验室坐标系的相对论变换，得到Gamma暴余辉的光变曲线。对于火球壳层的不同的动力学演化规律，各向同性或各向异性的壳层抛出形式，以及不同的外部介质环境，所得到的光变曲线都各不相同。通过对这些不同的光变曲线的比较，明确了Gamma暴余辉的整体的物理演化图象以及各种物理过程在Gamma暴余辉演化过程中所起的作用，并从余辉演化的方面进一步理解了Gamma暴的物理本质。     

Swift时代伽马暴的观测及研究进展

Swift卫星从2004年11月20日升空开始运转到现在已有2年多时间.到目前为止,它-共观测到了200多个伽马暴及其余辉现象.由于Swift观测到了早期X射线余辉、短暴余辉和高红移伽马暴等新的重要现象,伽马暴研究进入了新的时代.该文首先对伽马暴的研究历史做简短回顾,然后简要介绍伽马暴的物理图像和Swift卫星的构成及特点,最后全面评述Swift的观测成就及由此引起的理论挑战.     

伽玛射线暴及其余辉研究进展

伽玛射线暴是一种来自宇宙空间随机方向的短时间内伽玛射线突然增亮的现象。伽玛射线暴虽然早在1967年就由Vela卫星观测到,但直到1997年人们才通过余辉观测确定其寄主星系,并通过寄主星系的红移最终确定了伽玛射线暴的宇宙学起源。对伽玛射线暴研究概况进行了评述:详细介绍了伽玛射线暴及其余辉的观测进展,特别是近期Swift卫星和Fermi卫星带来的新发现;系统描述了伽玛射线暴标准火球模型、伽玛射线暴余辉物理(相对论性外流与暴周环境介质的相互作用过程、辐射产生机制等)及伽玛射线暴的前身星等。也对伽玛射线暴的未来研究进行了展望。     

Detecting radio afterglows of gamma-ray bursts with FAST

Using the generic hydrodynamic model of gamma-ray burst(GRB) afterglows, we calculate the radio afterglow light curves of low luminosity, high luminosity,failed and standard GRBs in different observational bands of FAST’s energy window.The GRBs are assumed to be located at different distances from us. Our results rank the detectability of GRBs in descending order as high luminosity, standard, failed and low luminosity GRBs. We predict that almost all types of radio afterglows except those of low luminosity GRBs could be observed by a large radio telescope as long as the domains of time and frequency are appropriate. It is important to note that FAST can detect relatively weak radio afterglows at a higher frequency of 2.5 GHz for very high redshift up to z = 15 or even more. Radio afterglows of low luminosity GRBs can only be detected after the completion of the second phase of FAST. FAST is expected to significantly expand the sample of GRB radio afterglows in the near future.     

伽玛暴及其早期X射线余辉的观测特征

Swift卫星的X射线望远镜观测揭示部分伽玛暴的早期余辉光变曲线有一个缓慢衰减的成分,而相当一部分却没有这样的成分.研究比较这两种暴的观测性质发现两类暴的持续时间、伽玛辐射总流量、谱指数、谱硬度比峰值能量等物理量均没有显著差异.然而有该成分的那些伽玛暴谱比较软、早期X射线余辉比较弱、伽玛射线辐射效率显著高于没有这个成分的那些暴.结果表明两类暴的前身星和中心机制一致,是否呈现这个缓慢衰减成分可能取决于外部介质.     

磁星能量注入模型拟合伽玛射线暴X射线余辉光变曲线

某些伽玛射线暴(简称伽玛暴)的中心致密天体可能是一颗具有强磁场的毫秒脉冲星,它通过磁偶极辐射可对伽玛暴外激波注入能量,从而导致早期余辉光变曲线的变平.近年来,从Swift卫星观测到的大量伽玛暴X射线余辉中发现,很多X射线余辉光变曲线在暴后10~2～10~4s期间的确存在明显的变平现象.利用周期为毫秒量级的磁星能量注入模型对11个加玛暴的X射线余辉光变曲线进行了拟合,显示该模型在解释余辉变平现象上的有效性和广泛性,通过对余辉光变曲线的拟合,同时也给出了相关中心磁星的磁场强度和旋转周期.     

Fitting X-ray Afterglow Light curves of Gamma-ray Bursts by Using the Magnetar Energy Injection Model

The central compact object for some gamma-ray bursts (GRBs) may be a strongly magnetized millisecond pulsar. It can inject energy to the outer shock of the GRB by through the magnetic dipole radiation, and therefore causes the shallow decay of the early afterglow. Recently, from a large number of GRB X-ray afterglows observed by Swift/XRT(X-ray telescope), it is revealed that many of them exhibit the shallow decay about 10²∼10⁴ s after the burst prompt emission. We have fitted the X-ray afterglow light curves of 11 GRBs by using the energy injection model of a magnetar with the rotation period in the millisecond order of magnitude. The obtained result shows the validity and universality of the magnetar energy injection model in explaining the shallow decay of afterglows, and simultaneously provides some constraints on the magnetic field strength and rotation period of the central magnetar.     

Observational Characteristics of γ-ray Bursts and Their Early X-ray Afterglows

Data obtained by the on-board X-ray telescope of the Swift satellite show that a shallow decay component is present in the light curve of the early X-ray afterglows of some γ-ray bursts (GRBs), but not in others. The physical mechanism of this component is debatable. We have made a comparative study on the observational characteristics of the two kinds of GRBs for a sample of 29 GRBs. Our results demonstrate that the two kinds of GRBs have no significant difference in the burst duration, γ-ray flux, spectral index, hardness ratio and peak energy. However, a significant difference exists in the early X-ray afterglows of the bursts: the bursts with a shallow decay component tend to have a softer and fainter X-ray afterglow than those without a shallow decay component. The efficiency of the γ-ray radiation is also very different for the two kinds of bursts: it is obviously higher for the bursts with a shallow decay component than those without. These results seem to suggest that the progenitors and central engines of the two kinds of GRBs are similar, and that the appearance of the shallow decay component is probably due to the surrounding medium.     

The Synchrotron-self-Compton Radiation Accompanying Shallow Decaying X-Ray Afterglow： the Case of GRB 940217

High energy emission (> tens MeV) of Gamma-Ray Bursts (GRBs) provides an important clue on the physical processes occurring in GRBs that may be correlated with the GRB early afterglow. A shallow decline phase has been well identified in about half of Swift Gamma-ray Burst X-ray afterglows. The widely considered interpretation involves a significant energy injection and possibly time-evolving shock parameter(s). We calculate the synchrotron-self-Compton (SSC) radiation of such an external forward shock and show that it could explain the well-known long term high energy (i.e., tens MeV to GeV) afterglow of GRB 940217. We propose that cooperation of Swift and GLAST will help to reveal the nature of GRBs.     

Gamma—Ray Bursts：Afterglows and Central Engines

Gamma-ray bursts (GRBs) are the most intense transient gamma-ray events in the sky; this, together with the strong evidence (the isotropic and inhomogeneous distribution of GRBs detected by BASTE) that they are located at cosmological distances, makes them the most energetic events ever known. For example, the observed radiation energies of some GRBs are equivalent to the total convertion into radiation of the mass energy of more than one solar mass. This is thousand times stronger than the energy of a supernova explosion. Some unconventional energy mechanism and extremely high conversion efficiency for these mysterious events are required. The discovery of host galaxies and association with supernovae at cosmoligical distances by the recently launched satellite of BeppoSAX and ground based radio and optical telescopes in GRB afterglow provides further support to the cosmological origin of GRBs and put strong constraints on their central engine. It is the aim of this article to review the possible central engines, energy mechanisms, dynamical and spectral evolution of GRBs, especially focusing on the afterglows in multi-wavebands.     

Hyperaccretion after the Blandford-Znajek Process： A New Model for GRBs with X-Ray Flares Observed in Early Afterglows

We propose a three-stage model with Blandford-Znajek (BZ) and hyperaccretion process to interpret the recent observations of early afterglows of Gamma-Ray Bursts (GRBs). In the first stage, the prompt GRB is powered by a rotating black hole (BH) invoking the BZ process. The second stage is a quiet stage, in which the BZ process is shut off, and the accretion onto the BH is depressed by the torque exerted by the magnetic coupling (MC) process. Part of the rotational energy transported by the MC process from the BH is stored in the disk as magnetic energy. In the third stage, the MC process is shut off when the magnetic energy in the disk accumulates and triggers magnetic instability. At this moment, the hyperaccretion process may set in, and the jet launched in this restarted central engine generates the observed X-ray flares. This model can account for the energies and timescales of GRBs with X-ray flares observed in early afterglows.     

X-ray plateaus followed by sharp drops in GRBs 060413, 060522, 060607A and 080330： Further evidences for central engine afterglow from gamma-ray bursts

The X-ray afterglows of GRBs 060413, 060522, 060607A and 080330 are characterized by a plateau followed by a very sharp drop. The plateau could be explained within the framework of the external forward shock model but the sharp drop can not.We interpret the plateau as the afterglows of magnetized central engines, plausibly magnetars. In this model, the X-ray afterglows are powered by the internal magnetic energy dissipation and the sudden drop is caused by the collapse of the magnetar. Accordingly,the X-ray plateau photons should have a high linear polarization, which can be tested by future X-ray polarimetry.     

Gamma-ray burst efficiency and possible physical processes shaping the early afterglow

The discovery by Swift that a good fraction of gamma-ray bursts (GRBs) have a slowly decaying X-ray afterglow phase led to the suggestion that energy injection into the blast wave takes place several hundred seconds after the burst. This implies that right after the burst the kinetic energy of the blast wave was very low and in turn the efficiency of production of γ-rays during the burst was extremely high, rendering the internal shocks model unlikely. We re-examine the estimates of kinetic energy in GRB afterglows and show that the efficiency of converting the kinetic energy into γ-rays is moderate and does not challenge the standard internal shock model. We also examine several models, including in particular energy injection, suggested to interpret this slow decay phase. We show that with proper parameters, all these models give rise to a slow decline lasting several hours. However, even those models that fit all X-ray observations, and in particular the energy injection model, cannot account self-consistently for both the X-ray and the optical afterglows of well-monitored GRBs such as GRB 050319 and GRB 050401. We speculate about a possible alternative resolution of this puzzle.