γ射线暴的最新研究进展:火球模型、余辉及前身星

γ射线暴 (称简γ暴 )的研究在最近几年里有了巨大的突破。观测上 ,人们发现了γ暴的低能余辉以及与γ射线爆发同时的光学爆发 ,还发现了它位于宇宙学距离的寄主星系。越来越多的观测证据还表明长时标γ暴与恒星形成区、甚至可能与超新星成协。在γ暴的相对论火球模型框架下 ,人们对γ暴以及余辉的产生机制的认识也有了进展。进而人们对γ暴的前身星以及环境效应等有了新的认识。本文旨在对这些进展和认识给一个扼要的评述     

γ射线暴的研究概况

γ射线暴是宇宙中自从大爆炸以来最猛烈的爆发现象，它在几十秒钟的时间内所释放的能量相当于太阳一生（约一百亿年）所释放能量的几百倍！文章简要介绍了γ射线暴的新近研究进展，其中包括：简要说明了观测事实，并在此基础上建立标准火球模型，阐述了γ射线暴及其余辉的运动和演化规律，讨论了偏离标准模型的种种观测现象以及这些后标准效应所包含的重要天体物理意义。进而讨论了至今仍不清楚的能源机制问题，也指出了这个领域的研究前景。     

2003年度重大科学成就--γ暴:大质量恒星的死亡

γ射线暴(简称γ暴)是宇宙中最剧烈的爆发事件，从20世纪60年代末被发现以来，它的起源问题就一直迷惑着人们，今年在γ暴研究上取得了几个突破性的进展，其中最重要的一个是直接确认了γ暴与超新星的关联，最终证实了γ暴起源于大质量恒星的死亡，这一重大发现被Nature和Science两个杂志同时评选为2003年度的十大科学成就之一。     

γ暴研究的重大突破：首次观测到γ暴的光学和X射线余辉

意大利和荷兰联合发射的卫星ＢｅｐｐｏＳＡＸ在１９９７年２月２８日探测到γ暴ＧＲＢ９７０２２８的Ｘ射线余辉，随后的地面和哈勃空间望远镜的观测证实在该位置上有一光学瞬变源。哈勃空间望远镜在此光学变源方位观测到一暗的河外天体。     

伽玛暴180620A外激波的能量注入研究

通过GRB 180620A研究伽玛射线暴余辉阶段的能量注入行为。通过数据拟合,我们发现GRB 180620A的X射线余辉存在一个平台,同时Swift的UVOT望远镜的观测也显示GRB 180620A的光学余辉存在一个平台结构。这个平台可能起源于中心引擎的能量注入。我们在这样的图像下,拟合了余辉的观测数据,并估计了瞬时辐射的辐射效率。     

寻找超高能宇宙线源——西藏广延空气簇射实验

总结了１９９０年６月到１９９３年１０月期间西藏空气簇射阵列的观测结果。寻找了来自于蟹状星云、Ｘ射线双星、脉冲星、活动星系核和其它活动天体的能量为１０ＴｅＶγ射线连续发射，没有发现连续稳定发射的迹象，但给出了每个源的流强上限。在阵列所观测的天区寻找了１０ＴｅＶ的γ暴，结果没有发现能量１０ＴｅＶ的γ暴，最后也给出了发现此种γ暴的上限。应用该阵列，明显地观测到了能量为１０ＴｅＶ的宇宙线流强的太阳和月亮阴影。观测了朝向和远离太阳的行星际空间磁场对宇宙线阴影的影响，这是行星际磁场对阴影位移影响的第一次直接观测。研究并发现在实验期间，太阳阴影的位置每年都在变化。同时观测在此期间，朝向和远离方向的宇宙线阴影的不同变化。另外，应用该实验的数据，给出了所谓的“膝”区的原初宇宙线能谱。     

宇宙γ射线暴

 γ射线暴(以下简称γ暴)是来自宇宙空间的一种短时标的高能γ射线爆发现象。它的发现颇有戏剧性:60年代中期,为了监督关于禁止在大气层中进行核试验的条约的执行情况,美国发射了一些卫星,以监测核爆炸中的γ射线事件。1967年开始,Ｖｅｌａ卫星真的不时记录到一些γ射线爆发现象,使美国政府十分紧张。军方花了几年的时间终于搞清楚它们均来自于宇宙空间,证实只是一场虚惊。由于军事保密的原因,该现象直到1973年才由美国洛斯阿拉莫斯实验室的Ｋｌｅｂｅｓａｄｅｌ、Ｓｔｒｏｎｇ和Ｏｌｓｏｎ在ＡｐＪ(美国《天体物理杂志》)的一篇快报中以“对源自宇宙空间的γ射线爆发的观测”为题发表出来。     

等离子体宇宙

几千年来,人们对宇宙的认识都是建立在可见光观测的基础上,而实际上可见光仅仅是电磁波谱中很窄的一段(0.4-0.8μm).近半个世纪以来,人们的视野开始扩展到红外和射电波段.最近十几年来迅速发展的空间技术,使天文学进入了全波段(即包括可见光、全部红外、紫外、x射线和γ射线的整个电磁波谱)观测.观测手段的进步使天体物理学家获得了以前从未有过的丰富信息,使人类对宇宙的认识在实质上发生了飞跃. x射线和γ射线的观测有着特别重要的意义.啊实上,从x射线和γ射线的观测,人们发现了许多出平意料的和有趣的现象.这些x射线和γ射线大部分是由能…     

用羊八井ASγ实验数据寻找TeV能区的γ射线暴

γ射线暴的TeV能区辐射对研究其起源、辐射机制等是非常重要的.利用西藏羊八井ASγ实验三期阵列的重建数据,通过在给定的小天区和时间间隔内寻找较高显著性事例团的方法对TeV能区的γ射线暴进行了寻找,在计算过程中采用“等天顶角法”来估计背景.工作中采用了两种途径来寻找γ射线暴,一种是与卫星γ射线暴的符合寻找,另一种是全天区独立寻找.结果发现少量事例团对背景有明显超出,考虑试验次数后,其超出还不足以认定为γ射线暴.通过Monte Carlo模拟,给出了在95%置信水平下,到达大气顶部流强上限的估计值为3.32×10^-9—1.24×10^-7 cm^-2s^-1. 关键词： γ射线暴 TeV能区 ASγ实验 宇宙射线     

寻找超高能宇宙线源——西藏广延空气簇射实验

总结了１９９０年６月到１９９３年１０月期间西藏空气簇射阵列的观测结果。寻找了来自于蟹状星云、Ｘ射线双星、脉冲星、活动星系核和其它活动天体的能量为１０ＴｅＶγ射线连续发射,没有发现连续稳定发射的迹象,但给出了每个源的流强上限。在阵列所观测的天区寻找了１０ＴｅＶ的γ暴,结果没有发现能量１０ＴｅＶ的γ暴,最后也给出了发现此种γ暴的上限。应用该阵列,明显地观测到了能量为１０ＴｅＶ的宇宙线流强的太阳和月亮阴影。观测了朝向和远离太阳的行星际空间磁场对宇宙线阴影的影响,这是行星际磁场对阴影位移影响的第一次直接观测。研究并发现在实验期间,太阳阴影的位置每年都在变化。同时观测在此期间,朝向和远离方向的宇宙线阴影的不同变化。另外,应用该实验的数据,给出了所谓的“膝”区的原初宇宙线能谱。     

Cosmic γ-ray bursts: Observations and modeling

It is now commonly accepted that cosmic γ-ray bursts (GRBs) are of cosmological origin. This conclusion is based on the statistical analysis of GRBs and the measurements of line redshifts in GRB optical afterglows, i.e., in the so-called long GRBs. In this review, the models of radiation and models of GRB sources are considered. In most of these models, if not in all of them, the isotropic radiation cannot provide the energy release necessary for the appearance of a cosmological GRB. No correlation is noted between the redshift, the GRB-spectrum shape, and the total detected energy. The comparison between data obtained in the Soviet experiment KONUS and the American experiment BATSE shows that they substantially differ in statistical properties and the detection of hard x-ray lines. The investigation of hard gamma (0.1–10 GeV) afterglows, the measurement of prompt optical spectra during the GRB detection, and the further investigation of hard x-ray lines is of obvious importance for gaining insight into the GRB origin. Observations of two bright optical GRB afterglows point to the fact that an initially bright optical flare is directly related to the GRB itself, and the subsequent weak and much more continuous optical radiation is of a different nature. The results of observations of optical GRB afterglows are discussed. They point to the fact that the GRBs originate in distant galaxies with a high matter density, where intense star formation takes place. The interaction of the cosmological GRB radiation with a dense surrounding molecular cloud results in the appearance of long-duration (up to 10 years) weak optical afterglows associated with the heating and reradiation of gas. Results of 2D numerical simulation of the heating and reradiation of gas in various variants of the relative disposition of GRB and molecular clouds are presented. In conclusion, the possible relation between the so-called short GRBs and recurrent sources of soft γ rays in our Galaxy, the so-called “soft gamma repeaters,” is discussed.     

Correlation between pulse-width and peak luminosity of single-pulse long gamma-ray bursts

With a sample of 21 single-pulse GRBs with redshift measurement and a sample of 65 single-pulse GRBs with pseudo redshift estimated by the luminosity-spectral lag relation, we show that the peak luminosities of GRB pulses are anti-correlated with pulse width, indicating that longer-pulses tend to be dimmer in the gamma-ray band. The anti-correlation is accessible with an internal shock scenario.     

Neutrinos of energy approximately 10(16) eV from gamma-ray bursts in pulsar wind bubbles

The supranova model for gamma-ray bursts (GRBs) is becoming increasingly more popular. In this scenario the GRB occurs weeks to years after a supernova explosion, and is located inside a pulsar wind bubble (PWB). Protons accelerated in the internal shocks that emit the GRB may interact with the external PWB photons producing pions which decay into approximately 10(16) eV neutrinos. A km(2) neutrino detector would observe several events per year correlated with the GRBs.     

Three years’ systematic GRB follow-up at the Xinglong Observatory and the optical afterglow observations of GRB 080330

We present a brief overview of follow-up observations of GRB afterglows made by the 0.8-m TNT and other telescopes at the Xinglong observatory during the last three years. Our system, dedicated to the measurement of early-time optical afterglow emission, responded to 50 GRBs from Jan. 2006 to Apr. 2009. Among them, about 50% have been successfully detected. The fastest response time is 76 sec (GRB 061110A and GRB 090426) after the space-borne GRB detector was triggered. The redshift distribution spans the range from z = 0.033 (GRB 060218) to z = 5.6 (GRB 060927). We also report the optical photometric follow-up of GRB 080330, which is an X-ray flash, as an example of our observations.     

Search for strong gravitational lensing effect in the current GRB data of BATSE

Because gamma-ray bursts(GRBs)trace the high-z universe,there is an appreciable probability for a GRB to be gravitational lensed by galaxies in the universe.Herein we consider the gravitational lensing effect of GRBs contributed by the dark matter halos in galaxies.Assuming that all halos have the singular isothermal sphere(SIS)mass profile in the mass range 1010h?1M?M2×1013h?1M?and all GRB samples follow the intrinsic redshift distribution and luminosity function derived from the Swift LGRBs sample,we calculated the gravitational lensing probability in BATSE,Swift/BAT and Fermi/GBM GRBs,respectively.With an derived probability result in BATSE GRBs,we searched for lensed GRB pairs in the BATSE5B GRB Spectral catalog.The search did not find any convincing gravitationally lensed events.We discuss our result and future observations for GRB lensing observation.     

SVOM gamma ray monitor

The space-based multi-band astronomical Variable Object Monitor (SVOM) mission is dedicated to the detection, localization and broad-band study of gamma-ray bursts (GRBs) and other high-energy transient phenomena. The gamma ray monitor (GRM) onboard is designed to observe GRBs up to 5 MeV. With this instrument, one of the key GRB parameters, E _peak, can be easily measured in the hard X-ray band. It can achieve a detection rate of 100 GRBs per year which ensures the scientific output of SVOM.     

Neutrinos from pulsar wind bubbles as precursors to gamma-ray bursts

The supranova model for gamma-ray bursts (GRBs) has recently gained popularity. In this scenario the GRB occurs weeks to years after a supernova explosion, and is located inside a pulsar wind bubble (PWB). High energy protons from the PWB can interact with photons from the rich radiation field inside the PWB or collide with cold protons from the supernova remnant, producing pions which decay into approximately 10-10(3) TeV neutrinos. The predicted neutrino flux from the PWBs that host the GRBs should be easily detectable by planned 1 km(2) detectors.     

Afterglow from GRB 070610/Swift J195509.6+261406: An explanation using the fireball model

GRB 070610, which is also named Swift J195509.6+261406, is a peculiar Galactic transient with significant variability on short timescales in both X-ray and optical light curves. One possible explanation is that GRB 070610/Swift J195509.6 + 261406 is a soft gamma-ray repeater (SGR) in our Galaxy. Here, we use the fireball model, which is usually recognized as the standard model of gamma-ray burst (GRB) afterglows, and the energy injection hypothesis to interpret the X-ray and optical afterglow light curves of GRB 070610/Swift J195509.6 + 261406. It is found that the model is generally consistent with observations.

     

Gamma-ray bursts at high and very high energies

Gamma-Ray Bursts (GRBs) are extra-galactic and extremely energetic transient emissions of gamma rays, which are thought to be associated with the death of massive stars or the merger of compact objects in binary systems. Their huge luminosities involve the presence of a newborn stellar-mass black hole emitting a relativistic collimated outflow, which accelerates particles and produces non-thermal emissions from the radio domain to the highest energies. In this article, I review recent progresses in the understanding of GRB jet physics above 100 MeV, based on Fermi observations of bright GRBs. I discuss the physical implications of these observations and their impact on GRB modeling, and I present some prospects for GRB observation at very high energies in the near future.