Fermi/GBM单峰长暴的FWHM相关关系研究

本文选取26个已知红移的单峰Fermi/GBM长暴,采用KRL模型拟合光变曲线计算出半峰全宽FWHM,探讨了FWHM相关的关系。发现伽马暴的FWHM与峰值能量Ep相关性不强,未明显发现之前利用BeppoSAX、Swift暴得到的结果。这意味着FWHM与峰值能量Ep的相关关系可能受探测仪器选择效应的影响。同时利用这些Fermi/GBM伽马暴样本,通过重新对FWHM与持续时间T做相关分析,结果发现,FWHM与T90、T50都存在较强的幂律关系,其相关系数分别为R=0.85、R=0.72。这表明FWHM与T90、T50存在这密切关系,同利用BeppoSAX、Swift暴得到的结果一致。     

Fermi伽马射线暴的光谱能量关系

基于Fermi卫星对伽马射线暴峰值能量探测灵敏度的提高,本文收集了Fermi卫星近8年的已知红移和E_(peak)的84个数据样本,再次分析Amati和Yonetoku关系。研究结果表明:Amati和Yonetoku关系可以分别用两条很好的直线拟合,对能量和光度关系进行了更新。大多数伽马射线暴的均质能量满足2.02×10~(54)erg量级,均质光度满足2.32×10~(52)erg量级。     

研究GBM和BAT同时触发的暴

结合Swift和Fermi两个卫星的各自优点,选择Fermi/GBM和Swift/BAT同时触发的伽玛暴观测数据,发现GBM暴持续时间的平均值比BAT暴要小,但是它们的持续时间分布、伽玛暴本身的流量分布以及光子峰值能量分布(log N-log P分布)之间不存在系统性差异.所以,不同仪器的观测差异可能是由于仪器本身的灵敏度引起的,与暴的性质无关.     

Fermi/GBM伽马暴的谱能关系

选取10个已知红移的单峰Fermi/GBM长暴,采用交叉相关函数计算第1与第3能道之间的相对能谱延迟(R_(SL)).研究发现,伽马暴的R_(SL)s分别与峰值光度和红移相关,所得结果与已报道文献中利用BATSE暴得到的结果相符合.这意味着R_(SL)与峰值光度和红移的相关关系不受探测仪器选择效应的影响.这表明R_(SL)可以作为一个可能的宇宙红移探测指示器用于宇宙学参数的测量.利用这些Fermi/GBM伽马暴样本,通过重新分析发现峰值能量与峰值光度、各向同性能存在较强相关.这些关系与从BATSE暴中得到的结果不一致,而与从Swift暴得到的结果符合.     

已知红移Fermi/LAT暴的谱能关系

Fermi卫星的GBM可以更精确地测量Epeak,以及LAT在GeV能段的定位和观测,提供了一个独特的研究伽玛暴谱能关系之一Eiso-Epeak关系的机会.根据9个具有红移的Fermi/LAT暴的谱能关系,发现长暴的这个关系满足一定的关系,而短暴却不满足.     

已知红移 Fermi/LAT 暴的谱能关系 林一清

Fermi卫星的GBM可以更精确地测量Epeak,以及LAT在GeV能段的定位和观测,提供了一个独特的研究伽玛暴谱能关系之-Eiso-Epeak关系的机会．根据9个具有红移的Fermi／LAT暴的谱能关系,发现长暴的这个关系满足一定的关系,而短暴却不满足．     

单峰结构的GRB光变曲线的FWHM与E_p之间的关系

探讨了观测有红移数据并具有单峰结构的伽玛射线暴(GRB)光变曲线的半高全宽(FWHM)与其光子峰值能量Ep之间的关系。用CGRO卫星与Swift观测到的具有单峰结构的并能被半经验公式——KRL模型所拟合,而且在BeppoSAX卫星、Swift和观测站观测有红移数据的25个FWHM数据与相对应的Ep进行相关分析。结果表明:单峰GRB光变曲线的FWHM与光子峰值能量Ep的对数值之间有很好的线性相关性,相关系数R=-0.77。这表明GRB的光变曲线结构与其峰值能量有密切的关系,光变曲线的FWHM越宽,则峰值能量越低。     

史瓦西黑洞外中微子主导吸积盘的质量

选取2005年1月—2016年12月期间具有X射线余辉观测的16个γ射线暴的短暴数据样本,估算史瓦西黑洞外中微子主导吸积盘的质量,发现大部分盘的质量远大于模拟的最大值。这个结果表明,短暴要求更大质量的吸积盘,即史瓦西黑洞的吸积不足以提供多数短暴能量,短暴爆发所需要的能量可能需要黑洞的自旋或其他的电磁动力学过程来提供。     

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。     

短暴对应中微子主导吸积盘的盘质量

短暴最有可能起源于双致密星并合.因为这种情形产生的吸积盘较小,持续时间可以和短暴的持续时标相当.模拟结果显示,双星并合产生的吸积盘质量远低于双星质量的总和.本文利用现有的观测数据,估算了恒星级黑洞周围中微子主导吸积盘的质量.结果显示,短暴吸积盘质量的估算主要取决于它的喷流能量和张角及黑洞的质量和自旋.一些短暴要求具有很大质量的吸积盘,这个数值已经达到甚至超过了模拟的最大值.我们认为,可能存在其他的电磁动力学过程或者其他的机制可以提高中微子辐射效率,从而提供短暴爆发所需要的能量.     

SWIFT伽玛暴的谱延迟距离指示器

早期研究发现,BASTE长暴的相对谱延迟RSL是一个有用的宇宙距离指示器。本文从SWIFT卫星数据中,挑选10个单脉冲长伽玛暴(T90>2.6)作为样本,对样本进行降噪和去除背景,用交叉相关函数分析1,3能道的谱延迟,通过拟合研究各脉冲参数Asymmetry,Fm,Fp,tm,FWHM,τ31和相对谱延迟的关系,发现相对谱延迟和红移具有很好的相关性,这充分表明SWIFT长暴的相对谱延迟仍然是一个很好的红移指示器。     

An origin for short gamma-ray bursts unassociated with current star formation

Two short (< 2 s) gamma-ray bursts (GRBs) have recently been localized and fading afterglow counterparts detected. The combination of these two results left unclear the nature of the host galaxies of the bursts, because one was a star-forming dwarf, while the other was probably an elliptical galaxy. Here we report the X-ray localization of a short burst (GRB 050724) with unusual gamma-ray and X-ray properties. The X-ray afterglow lies off the centre of an elliptical galaxy at a redshift of z = 0.258 (ref. 5), coincident with the position determined by ground-based optical and radio observations. The low level of star formation typical for elliptical galaxies makes it unlikely that the burst originated in a supernova explosion. A supernova origin was also ruled out for GRB 050709 (refs 3, 31), even though that burst took place in a galaxy with current star formation. The isotropic energy for the short bursts is 2-3 orders of magnitude lower than that for the long bursts. Our results therefore suggest that an alternative source of bursts--the coalescence of binary systems of neutron stars or a neutron star-black hole pair--are the progenitors of short bursts.     

A giant gamma-ray flare from the magnetar SGR 1806-20

Two classes of rotating neutron stars-soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars-are magnetars, whose X-ray emission is powered by a very strong magnetic field (B approximately 10(15) G). SGRs occasionally become 'active', producing many short X-ray bursts. Extremely rarely, an SGR emits a giant flare with a total energy about a thousand times higher than in a typical burst. Here we report that SGR 1806-20 emitted a giant flare on 27 December 2004. The total (isotropic) flare energy is 2 x 10(46) erg, which is about a hundred times higher than the other two previously observed giant flares. The energy release probably occurred during a catastrophic reconfiguration of the neutron star's magnetic field. If the event had occurred at a larger distance, but within 40 megaparsecs, it would have resembled a short, hard gamma-ray burst, suggesting that flares from extragalactic SGRs may form a subclass of such bursts.     

The afterglow and elliptical host galaxy of the short gamma-ray burst GRB 050724

Despite a rich phenomenology, gamma-ray bursts (GRBs) are divided into two classes based on their duration and spectral hardness--the long-soft and the short-hard bursts. The discovery of afterglow emission from long GRBs was a watershed event, pinpointing their origin to star-forming galaxies, and hence the death of massive stars, and indicating an energy release of about 10(51) erg. While theoretical arguments suggest that short GRBs are produced in the coalescence of binary compact objects (neutron stars or black holes), the progenitors, energetics and environments of these events remain elusive despite recent localizations. Here we report the discovery of the first radio afterglow from the short burst GRB 050724, which unambiguously associates it with an elliptical galaxy at a redshift z = 0.257. We show that the burst is powered by the same relativistic fireball mechanism as long GRBs, with the ejecta possibly collimated in jets, but that the total energy release is 10-1,000 times smaller. More importantly, the nature of the host galaxy demonstrates that short GRBs arise from an old (> 1 Gyr) stellar population, strengthening earlier suggestions and providing support for coalescing compact object binaries as the progenitors.     

An origin in the local Universe for some short gamma-ray bursts

Gamma-ray bursts (GRBs) divide into two classes: 'long', which typically have initial durations of T90 > 2 s, and 'short', with durations of T90 < 2 s (where T90 is the time to detect 90% of the observed fluence). Long bursts, which on average have softer gamma-ray spectra, are known to be associated with stellar core-collapse events-in some cases simultaneously producing powerful type Ic supernovae. In contrast, the origin of short bursts has remained mysterious until recently. A subsecond intense 'spike' of gamma-rays during a giant flare from the Galactic soft gamma-ray repeater, SGR 1806-20, reopened an old debate over whether some short GRBs could be similar events seen in galaxies out to approximately 70 Mpc (refs 6-10; redshift z approximately 0.016). Shortly after that, localizations of a few short GRBs (with optical afterglows detected in two cases) have shown an apparent association with a variety of host galaxies at moderate redshifts. Here we report a correlation between the locations of previously observed short bursts and the positions of galaxies in the local Universe, indicating that between 10 and 25 per cent of short GRBs originate at low redshifts (z < 0.025).     

An apparently normal gamma-ray burst with an unusually low luminosity

Much of the progress in understanding gamma-ray bursts (GRBs) has come from studies of distant events (redshift z approximately 1). In the brightest GRBs, the gamma-rays are so highly collimated that the events can be seen across the Universe. It has long been suspected that the nearest and most common events have been missed because they are not as collimated or they are under-energetic (or both). Here we report soft gamma-ray observations of GRB 031203, the nearest event to date (z = 0.106; ref. 2). It had a duration of 40 s and peak energy of >190 keV, and therefore appears to be a typical long-duration GRB. The isotropic gamma-ray energy of < or =10(50) erg, however, is about three orders of magnitude smaller than that of the cosmological population. This event--as well as the other nearby but somewhat controversial GRB 980425--is a clear outlier from the isotropic-energy/peak-energy relation and luminosity/spectral-lag relations that describe the majority of GRBs. Radio calorimetry shows that both of these events are under-energetic explosions. We conclude that there does indeed exist a large population of under-energetic events.     

中国上市公司资本成本和资本结构实证分析

采用深沪股市1999－2000年的相应数据,在考虑了“资产重组”这一因素后,对样本进行筛选,运用实证研究的方法,对资本成本与资本结构的关系进行了横截面分析,在研究中,鉴于短期债务在我国的特殊性,分别考察了长期财务杠杆和短期财务工作对资本成本的影响,并得出以下几点分析结论：长期财务杠杆对权益资本成本和加权资本成本的影响不显著,短期财务杠杆与权益资本成本和加权平均资本成本显著正相关,企业规模对权益资本成本和加权平均资本成本有显著的正面影响。     

一般Boole格的单点扩张Boole—最小扩张Boole格

对一般Ｂｏｏｌｅ格Ｌ，利用其Ｓｔｏｎｅ空间的特征已讨论了Ｌ的单点扩张Ｂｏｏｌｅ格Ｅｐ（Ｌ）［１］。在其代数结构上并未给出Ｅｐ（Ｌ）与Ｌ之间的关系．现从代数结构上讨论一般Ｂｏｏｌｅ格的扩张，而且给出了一般Ｂｏｏｌｅ格的最小扩张Ｂｏｏｌｅ格．     

SWift 3D与Flash联用制作与修饰三维化学粒子模型

介绍了Flash与Swift 3D的基本特点与联用关系.以甲烷分子为例,探讨用Swift 3D制作3D分子模型单元,并将其导入Flash中进行修饰,以实现动态化学粒子模型的空间三维多角度展示.