特殊伽玛暴及伽玛暴的特殊辐射成分

伽玛射线暴(伽玛暴)的探测从其被发现以来,已经获得了大量的伽玛射线观测结果以及多波段的余辉观测结果,但是X射线能区的爆发阶段的瞬时辐射还比较缺乏观测数据.爱因斯坦探针(EP)是软X射线能区(0.5–4 keV)的大视场(1.1 sr)望远镜,为伽玛暴的X射线瞬时辐射的观测带来全新的时间窗口.本文讨论了EP对富X射线辐射的特殊伽玛暴或伽玛暴的特殊辐射成分进行了预期研究,特别是研究了X射线闪、低光度伽玛暴、超长伽玛暴和伽玛暴的先兆辐射.我们发现,EP预期能每年探测到约810个伽玛暴类爆发事件,其中95%为能谱较软的X射线闪,将近1%为典型伽玛暴;EP预期能每年探测到0.2–8个低光度伽玛暴,具体探测率依赖于低光度暴能谱硬度的分布;EP预期每年至少能探测到20–200个超长伽玛暴;EP有望探测到大量的、目前人们非常缺乏了解的伽玛暴先兆辐射,至少每年80个事件.综合这些情况,预计EP将对伽玛暴的分类、前身星特性、爆发机制和喷流特性等方面的研究具有重要意义.     

不同喷流模型的伽玛暴射电余辉研究

伽玛射线暴(又称伽玛暴)余晖对应的外流物质结构可用锥形模型、柱形模型或者双成份喷流模型来描述。随着世界上最大的单口径球面射电天文望远镜(FAST)的建成,利用大望远镜在射电波段甄别这些不同的伽玛暴余辉喷流模型将成为可能。本文将研究这些不同喷流模型的射电余晖光变曲线,并探讨FAST望远镜对这些类型伽玛暴余晖探测的可能性。     

伽玛射线暴的高能辐射

伽玛暴是宇宙中最剧烈的恒星级高能爆发现象,一般被认为产生于大质量恒星死亡(一些爆发时标长于2 s的伽玛暴在观测上被证实与一类特殊的超新星成协)或者双致密星(比如双中子星系统)并合(这类并合时标很短,可产生时标短于2 s的伽玛暴).工作在8 ke V–300 Ge V能段的Fermi伽玛射线空间望远镜自2008年升空工作之后,伽玛暴瞬时辐射和高能辐射研究取得了重要进展.本综述将介绍Fermi卫星在过去几年内关于伽玛暴领域的一些重要观测结果,并着重介绍这些观测对探索伽玛暴物理(伽玛暴外流体的光球辐射、磁化、Ge V高能辐射起源),特别是Fermi卫星大面积望远镜(LAT)的高能(100 Me V)辐射观测对限制伽玛暴初始速度/洛伦兹因子,限制宇宙河外背景光模型以及检验光速不变原理等方面的主要研究进展.     

伽玛暴光学余辉中的双喷流成份行为

伽玛暴余辉的双拐折行为可以用双喷流成份结构模型得到较好的解释,但至今其物理参数还未解。为给出其相应的物理参数,文中将对具有双喷流成份的伽玛暴光学余辉进行统计分析,用外激波模型时域指数α和频域指数β的关系(closure relation)对数据进行限制,得到GRB 071003,GRB 080319B,GRB 090426和GRB 100219A共4个具有外激波模型的伽玛暴双成份喷流特征。这些伽玛暴第一个喷流成份的张角都在1°以内,而第二个喷流成份的张角增大到2°~7°,与单成份喷流的张角一致。其各向同性辐射能量在1051~1054erg,电子谱指数p约为2,比典型值2.3硬。长暴能较好符合Amati关系。     

爱因斯坦探针卫星的核塌缩超新星激波暴探测

在核塌缩超新星爆发过程中,当辐射主导的爆炸激波传播到前身星表面附近时,高温辐射逃逸形成激波暴,是超新星最早的电磁信号.激波暴热辐射以紫外和软X射线光子为主,持续时间短暂(~10–1000 s),仅有几个疑似观测事例.爱因斯坦探针卫星开展的大视场、高灵敏度的软X射线快速全天巡天,预期每年将获得几十颗II-P型超新星的激波暴光变曲线,对蓝超巨星爆发和Ib/Ic型超新星的激波暴合计也可能有一到数颗的年探测率,有望用于限制前身星类型、爆前物质损失、超新星爆发机制等.     

引力波事件GW170817的电磁对应体

2017年8月17日,激光干涉引力波天文台(LIGO)首次探测到来自双中子星合并的引力波GW170817.伴随GW170817的短伽玛射线暴与千新星也分别在1.74 s后和10.9 h后被伽玛射线卫星和光学望远镜探测到.对这些电磁对应体的观测与研究首次证实双中子星并合会产生大量重元素并形成千新星.通过相关理论与观测的比较,人们对于双中子星并合的中心引擎、短伽玛暴喷流的特性以及并合产生的抛射物性质等一系列重要的天体物理学问题进行了空前深入的研究.本文介绍伴随GW170817的各类电磁波对应体的性质,并探讨这些电磁波对应体的物理起源.     

伽玛射线噪Blazar的亮温度研究

通过Blazar的伽玛射线光度与亮温度的关系讨论了伽玛辐射的喷流效应.从一些文献中收集了50个伽玛射线噪Blazar天体的伽玛射线、X射线资料和相应的亮温度.该样本中包括16个蝎虎天体(BL Lac)和34个平谱射电类星体(FSRQs).研究了光度与亮温度之间的关系,结果表明亮温度与伽玛射线和X射线光度都存在相关,这一结果说明伽玛射线和X射线都具有强喷流效应.     

高红移爆发源作为早期宇宙和第一代天体的探针

伽玛暴是宇宙中最为明亮的爆发现象,由于它们的高光度,人们可探测到发生在极早期宇宙处的伽玛暴.高红移伽玛暴可作为宇宙深处的灯塔,它们是探索早期宇宙性质的理想工具.利用高红移伽玛暴可以限制暗能量和宇宙学参数,测量高红移的恒星形成率,揭示第一代天体的性质,研究宇宙再电离和金属增丰历史.因此,高红移伽玛暴的观测具有重要的科学意义.相比目前的探测卫星,爱因斯坦探针(EP)拥有更高的灵敏度和更宽的观测视场,且主要观测能段为软X射线波段(0.5–4 keV),非常适合高红移伽玛暴的观测.考虑EP的能力和观测模式,并且借助能够很好解释目前Swift卫星的伽玛暴观测样本的理论模型,详细计算了未来EP对高红移伽玛暴的可能探测率.我们预测EP对z6伽玛暴的探测率约为20 events yr~(-1) sr~(-1),对z8伽玛暴的探测率约为6 events yr~(-1) sr~(-1),对z12伽玛暴的探测率约为1 events yr~(-1) sr~(-1).估计在3年的运行时间内,EP将能探测到约65个z6的伽玛暴,其中包括~20个z8的伽玛暴和~3个z12的伽玛暴.总之,EP有望显著提高高红移伽玛暴的观测能力,这些丰富的观测信息将很有可能揭开早期宇宙的部分科学谜团.     

GRB 980703射电、光学和红外余辉的数值模拟研究

GRB 980703有丰富的多波段余辉观测数据. 特别是它的射电余辉非常明亮以至于在爆发后1000多天还能被观测到. 此外, 它的多波段余辉光变曲线中没有特殊的特征, 也就是说没有增亮、平台、快速衰减或缓慢衰减等现象. 以上这些特点使得GRB 980703成为伽玛暴研究领域中一个十分难得的样本. 在本文中利用GRB 980703的观测数据来详细地检验伽玛暴余辉的标准火球模型, 计算结果表明火球模型可以满意地解释伽玛暴多波段余辉光变曲线的行为. 拟合得到的GRB 980703的物理参数如下： 喷流的半张角约为Θ0≈0.23 radian; 暴周围环境介质密度约为n≈27cm-3; 火球各向同性总能量约为E0≈3.8×1052 ergs; 伽玛暴寄主星系对视线方向的消光贡献约为AV≈2.5 mag.     

伽玛射线暴内光度和峰值能量关系的统计分析

以前的研究表明:在伽玛射线暴(简称伽玛暴)间各向同性等值光度Liso和静止系中vFv谱的峰值能量E′p之间存在关系式LisooE′p2.Liang等人用Preece等人给出的91个BATSE伽玛暴的2408个时间分辨谱样本对这一关系式进行了验证,得出这一关系式不但在伽玛暴内成立,而且在伽玛暴之间也是成立的.为了进一步验证这一关系式,我们收集了Kaneko等人2006年发表的350个BATSE伽玛暴能谱的数据,并对其中185个伽玛暴能谱的5218个时间分辨谱样本进行统计分析,我们得出的结果与Liang等人的结果是一致的.     

Evolution of the polarization of the optical afterglow of the gamma-ray burst GRB030329

The association of a supernova with GRB030329 strongly supports the 'collapsar' model of gamma-ray bursts, where a relativistic jet forms after the progenitor star collapses. Such jets cannot be spatially resolved because gamma-ray bursts lie at cosmological distances; their existence is instead inferred from 'breaks' in the light curves of the afterglows, and from the theoretical desire to reduce the estimated total energy of the burst by proposing that most of it comes out in narrow beams. Temporal evolution of the polarization of the afterglows may provide independent evidence for the jet structure of the relativistic outflow. Small-level polarization ( approximately 1-3 per cent) has been reported for a few bursts, but its temporal evolution has yet to be established. Here we report polarimetric observations of the afterglow of GRB030329. We establish the polarization light curve, detect sustained polarization at the per cent level, and find significant variability. The data imply that the afterglow magnetic field has a small coherence length and is mostly random, probably generated by turbulence, in contrast with the picture arising from the high polarization detected in the prompt gamma-rays from GRB021206 (ref. 18).     

The association of GRB 060218 with a supernova and the evolution of the shock wave

Although the link between long gamma-ray bursts (GRBs) and supernovae has been established, hitherto there have been no observations of the beginning of a supernova explosion and its intimate link to a GRB. In particular, we do not know how the jet that defines a gamma-ray burst emerges from the star's surface, nor how a GRB progenitor explodes. Here we report observations of the relatively nearby GRB 060218 (ref. 5) and its connection to supernova SN 2006aj (ref. 6). In addition to the classical non-thermal emission, GRB 060218 shows a thermal component in its X-ray spectrum, which cools and shifts into the optical/ultraviolet band as time passes. We interpret these features as arising from the break-out of a shock wave driven by a mildly relativistic shell into the dense wind surrounding the progenitor. We have caught a supernova in the act of exploding, directly observing the shock break-out, which indicates that the GRB progenitor was a Wolf-Rayet star.     

A link between prompt optical and prompt gamma-ray emission in gamma-ray bursts

The prompt optical emission that arrives with the gamma-rays from a cosmic gamma-ray burst (GRB) is a signature of the engine powering the burst, the properties of the ultra-relativistic ejecta of the explosion, and the ejecta's interactions with the surroundings. Until now, only GRB 990123 had been detected at optical wavelengths during the burst phase. Its prompt optical emission was variable and uncorrelated with the prompt gamma-ray emission, suggesting that the optical emission was generated by a reverse shock arising from the ejecta's collision with surrounding material. Here we report prompt optical emission from GRB 041219a. It is variable and correlated with the prompt gamma-rays, indicating a common origin for the optical light and the gamma-rays. Within the context of the standard fireball model of GRBs, we attribute this new optical component to internal shocks driven into the burst ejecta by variations of the inner engine. The correlated optical emission is a direct probe of the jet isolated from the medium. The timing of the uncorrelated optical emission is strongly dependent on the nature of the medium.     

γ射线暴火球模型的光学余辉辐射

按照γ射线暴火球模型的动力学演化规律,利用相对论电子在磁场中作同步加速辐射时谱分布的特点,用求峰值频率辐射的方法,计算了γ射线暴红光波段余辉辐射流量随时间的变化与γ射线暴GRB970228的观测结果比较,符合甚好,说明同步加速辐射是γ射线暴余辉主要的辐射机制,也进一步证明了火球模型的正确。     

Energy input and response from prompt and early optical afterglow emission in gamma-ray bursts

The taxonomy of optical emission detected during the critical first few minutes after the onset of a gamma-ray burst (GRB) defines two broad classes: prompt optical emission correlated with prompt gamma-ray emission, and early optical afterglow emission uncorrelated with the gamma-ray emission. The standard theoretical interpretation attributes prompt emission to internal shocks in the ultra-relativistic outflow generated by the internal engine; early afterglow emission is attributed to shocks generated by interaction with the surrounding medium. Here we report on observations of a bright GRB that, for the first time, clearly show the temporal relationship and relative strength of the two optical components. The observations indicate that early afterglow emission can be understood as reverberation of the energy input measured by prompt emission. Measurements of the early afterglow reverberations therefore probe the structure of the environment around the burst, whereas the subsequent response to late-time impulsive energy releases reveals how earlier flaring episodes have altered the jet and environment parameters. Many GRBs are generated by the death of massive stars that were born and died before the Universe was ten per cent of its current age, so GRB afterglow reverberations provide clues about the environments around some of the first stars.     

同步自吸收对Gamma射线暴余辉的影响

考虑同步自吸收效应后,讨论了Gamma射线暴余辉的谱并展示了Gamma射线暴GRB970508余辉在光学波段的光变曲线,尽管光学余辉很复杂,所得到的结果仍然与观测结果符合的很好,因此不管是在火球＋激波模型还是在喷流模型中,都应该全面地研究同步自吸收效应和内部能源机制,以使理论计算更好的拟合观测到的光变曲线。     

The sub-energetic gamma-ray burst GRB 031203 as a cosmic analogue to the nearby GRB 980425

Over the six years since the discovery of the gamma-ray burst GRB 980425, which was associated with the nearby (distance approximately 40 Mpc) supernova 1998bw, astronomers have debated fiercely the nature of this event. Relative to bursts located at cosmological distance (redshift z approximately 1), GRB 980425 was under-luminous in gamma-rays by three orders of magnitude. Radio calorimetry showed that the explosion was sub-energetic by a factor of 10. Here we report observations of the radio and X-ray afterglow of the recent GRB 031203 (refs 5-7), which has a redshift of z = 0.105. We demonstrate that it too is sub-energetic which, when taken together with the low gamma-ray luminosity, suggests that GRB 031203 is the first cosmic analogue to GRB 980425. We find no evidence that this event was a highly collimated explosion viewed off-axis. Like GRB 980425, GRB 031203 appears to be an intrinsically sub-energetic gamma-ray burst. Such sub-energetic events have faint afterglows. We expect intensive follow-up of faint bursts with smooth gamma-ray light curves (common to both GRB 031203 and 980425) to reveal a large population of such events.     

一种FPGA通用布线开关盒模型

提出了一种基于通用布线开关盒(GRB)的新型FPGA布线结构,该结构能够有效提高FPGA布线资源利用率.与VPR中的CB/SB布线结构和CS-Box结构相比,GRB结构能够进一步改善布通率和时序性能.MCNC基准电路测试结果表明:在布线开关数目相同的前提下,GRB结构能够将FPGA的综合性能平均提高4%.通过在GRB互连结构中引入快速布线通道,该结构在开关数目比CS/SB模型增加10.92%的情况下,能将时序性能提升17.50%.     

γ爆发谱和γ爆发源

本文将γ爆发事件分成三类,并认为第二,三类γ爆源于老年中子星且爆发谱由热轫致辐射、磁轫致辐射以及湮灭辐射谱组成。结果表明:①我们的假定可很好地解释第二、三类γ爆;②发射谱的性状依赖于发射区的磁场;③对于每个γ爆,它源于同一中子星的不同发射区。     

喷水织机喷水动力学分析研究

通过对喷水织机喷水动力学的研究,分析出影响射水流速度大小的喷水机构参数并进行优化,以进一步提高射流的稳定性,提高喷水引纬的速度和适当扩大织幅,同时指出主要通过增大弹簧刚度（常数）和减小柱塞面积来提高喷水速度及增长有放喷水时间。