Ultra-relativistic electrons in Jupiter's radiation belts

Ground-based observations have shown that Jupiter is a two-component source of microwave radio emission: thermal atmospheric emission and synchrotron emission from energetic electrons spiralling in Jupiter's magnetic field. Later in situ measurements confirmed the existence of Jupiter's high-energy electron-radiation belts, with evidence for electrons at energies up to 20[?]MeV. Although most radiation belt models predict electrons at higher energies, adiabatic diffusion theory can account only for energies up to around 20[?]MeV. Unambiguous evidence for more energetic electrons is lacking. Here we report observations of 13.8[?]GHz synchrotron emission that confirm the presence of electrons with energies up to 50[?]MeV; the data were collected during the Cassini fly-by of Jupiter. These energetic electrons may be repeatedly accelerated through an interaction with plasma waves, which can transfer energy into the electrons. Preliminary comparison of our data with model results suggests that electrons with energies of less than 20[?]MeV are more numerous than previously believed.     

锥形飞秒强激光等离子体中Compton散射的能量转换

应用相对论性电子与多光子集团非弹性碰撞模型和经典相对论电动力学理论,分析、计算了锥形飞秒强激光等离子体中多光子非线性Compton散射的能量转换.发现等离子体中的耦合激光场会引起能量转换效率的振荡,而静电场会降低能量转换效率.当高能电子与光子发生双光子非线性Compton散射时,电子能获得最大的能量转换效率.     

TeV耀变体的高能伽玛射线辐射研究

基于双幂率电子谱,考虑了源内极端相对论性电子的逆康普顿散射过程和源外极端相对论性质子与背景光子相互作用(pγ相互作用)对高能伽玛射线辐射能谱的贡献。结合Fermi-LAT最新的观测结果,假定一个合理的电子谱和质子谱,将模型应用于TeV耀变体PKS 2155-304宁静态下的多波段辐射能谱。研究结果表明,上述过程能产生PKS 2155-304宁静态下的多波段辐射能谱,且pγ相互作用产生的次级辐射对高能伽玛射线能谱有明显的贡献。     

Gamma-ray bursts: huge explosion in the early Universe

Long gamma-ray bursts (GRBs) are bright flashes of high-energy photons that can last for tens of minutes; they are generally associated with galaxies that have a high rate of star formation and probably arise from the collapsing cores of massive stars, which produce highly relativistic jets (collapsar model). Here we describe gamma- and X-ray observations of the most distant GRB ever observed (GRB 050904): its redshift (z) of 6.29 means that this explosion happened 12.8 billion years ago, corresponding to a time when the Universe was just 890 million years old, close to the reionization era. This means that not only did stars form in this short period of time after the Big Bang, but also that enough time had elapsed for them to evolve and collapse into black holes.     

Blazar喷流中相对论电子的同步辐射过程

对于Blazar的相对论喷流,假设其中存在一个球形区域,相对论电子在该区域内在磁场的作用下将产生同步辐射。先对其发射系数和吸收系数等进行了计算,然后对它们与磁场和频率等的关系进行分析,并对同步辐射谱加以讨论。     

Birth of a relativistic outflow in the unusual γ-ray transient Swift J164449.3+573451

Active galactic nuclei, which are powered by long-term accretion onto central supermassive black holes, produce relativistic jets with lifetimes of at least one million years, and the observation of the birth of such a jet is therefore unlikely. Transient accretion onto a supermassive black hole, for example through the tidal disruption of a stray star, thus offers a rare opportunity to study the birth of a relativistic jet. On 25 March 2011, an unusual transient source (Swift J164449.3+573451) was found, potentially representing such an accretion event. Here we report observations spanning centimetre to millimetre wavelengths and covering the first month of evolution of a luminous radio transient associated with Swift J164449.3+573451. The radio transient coincides with the nucleus of an inactive galaxy. We conclude that we are seeing a newly formed relativistic outflow, launched by transient accretion onto a million-solar-mass black hole. A relativistic outflow is not predicted in this situation, but we show that the tidal disruption of a star naturally explains the observed high-energy properties and radio luminosity and the inferred rate of such events. The weaker beaming in the radio-frequency spectrum relative to γ-rays or X-rays suggests that radio searches may uncover similar events out to redshifts of z?≈?6.     

宇宙背景光子对Blazar高能伽马射线的吸收过程

Blazar高能伽马射线在宇宙传播过程中,将会和宇宙背景光子发生相互作用,从而能量会有一个降低的过程。文章将在理论上计算和分析宇宙微波背景（CMB）和河外背景光（EBL）对高能伽马射线的吸收过程,并讨论二者对不同红移情况下的高能伽马射线的吸收过程。     

The third family of compact stars with the color-flavor locked quark core

In this paper, we study the third family of compact stars with the color-flavor locked (CFL) quark core. The relativistic mean field model is used for hadronic matter and the MIT bag model for CFL quark matter. The results of the calculation show a transitional behavior that goes from the hadron star range, through the transition range, into the CFL quark star range. In the transition range, the third family of compact stars with the CFL quark matter core is found in the wide range of the CFL energy gap 100 MeV?Δ<150 MeV. By comparing with early investigations, we argue that the greatest possible third family of compact stars may be the hybrid stars with the CFL quark core.     

Polarization of the prompt gamma-ray emission from the gamma-ray burst of 6 December 2002

Observations of the afterglows of gamma-ray bursts (GRBs) have revealed that they lie at cosmological distances, and so correspond to the release of an enormous amount of energy. The nature of the central engine that powers these events and the prompt gamma-ray emission mechanism itself remain enigmatic because, once a relativistic fireball is created, the physics of the afterglow is insensitive to the nature of the progenitor. Here we report the discovery of linear polarization in the prompt gamma-ray emission from GRB021206, which indicates that it is synchrotron emission from relativistic electrons in a strong magnetic field. The polarization is at the theoretical maximum, which requires a uniform, large-scale magnetic field over the gamma-ray emission region. A large-scale magnetic field constrains possible progenitors to those either having or producing organized fields. We suggest that the large magnetic energy densities in the progenitor environment (comparable to the kinetic energy densities of the fireball), combined with the large-scale structure of the field, indicate that magnetic fields drive the GRB explosion.     

同步辐射技术和透射电镜技术以及密度泛函理论相结合的综合表征方法及其应用

同步辐射技术和透射电镜技术是研究材料的重要表征手段,广泛应用于物理、化学、材料、环境与能源等学科的前沿研究领域.这两种技术方法,其物理原理是光子和电子与材料的相互作用,包括光子在材料中的散射与吸收,电子的衍射与能量损失等,从而演化出各种具体表征手段.从物理本质看,基于量子力学的密度泛函理论,其本征函数可以与同步辐射X射线的衍射和透射电镜电子的衍射得到的电荷密度相对应,而其本征值则可以与同步辐射X射线的吸收谱和光电子谱以及透射电镜电子的能量损失谱得到的能级或能带信息相对应.这些对应关系使得这两种技术手段和理论计算方法可以互相验证也可以互相补充,从而对材料的结构和电子信息的分析更为全面细致.本文综述了同步辐射技术和透射电镜技术的进展,通过典型材料表征进行举例说明,这两种技术结合密度泛函理论,能够深入分析功能材料的晶体结构信息以及各种物理化学性能.最后展望了这三种方法相结合的未来发展趋势.     

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 acceleration of cosmic-ray protons in the supernova remnant RX J1713.7-3946

Protons with energies up to approximately 10(15) eV are the main component of cosmic rays, but evidence for the specific locations where they could have been accelerated to these energies has been lacking. Electrons are known to be accelerated to cosmic-ray energies in supernova remnants, and the shock waves associated with such remnants, when they hit the surrounding interstellar medium, could also provide the energy to accelerate protons. The signature of such a process would be the decay of pions (pi(0)), which are generated when the protons collide with atoms and molecules in an interstellar cloud: pion decay results in gamma-rays with a particular spectral-energy distribution. Here we report the observation of cascade showers of optical photons resulting from gamma-rays at energies of approximately 10(12) eV hitting Earth's upper atmosphere, in the direction of the supernova remnant RX J1713.7-3946. The spectrum is a good match to that predicted by pion decay, and cannot be explained by other mechanisms.     

强子气体产生的热光子

在 SPS、RHIC 和 LHC 碰撞能区,利用 SU（2）规范对称性,研究了强子物质中介子相互作用产生的热光子. 计算结果表明,在 SPS 能区,强子气体对热光子谱起到更重要的作用,在 205 MeV 初始温度条件下,强子气体热光子产额比夸克-胶子等离子体的产额高. 在 RHIC 和 LHC 能区,夸克-胶子等离子体的作用随碰撞能量的增加而逐渐变得重要.     

大型集装箱检测系统探测效率的MC模拟计算

为了研究各种不同能量和能谱分布的入射射线对于“大型集装箱辐射检测系统”成像质量的影响 ,通过采用Monte Carlo (MC)模拟方法 ,对该问题进行了计算求解。采用通用电子和光子模拟计算程序 EGS4,在保证足够的计算粒子数目的条件下 ,具有较高的计算精度。对 0 .8Me V单能光子和最大能量分别为 2 ,3,7Me V连续谱情况 ,从透射深度、丝分辨率和对比度灵敏度 3个方面加以分析和比较 ,给出了这 3个指标的数值范围 ,从而得到能量和能谱分布对系统成像质量的影响。这表明 MC方法能够应用于大型集装箱检测系统     

相对论粒子在晶格中相关散射

本文采用与粒子运动纵向分量相同的坐标系来考察相对论粒子同晶格原子相关碰撞及其量子辐射。通过相对论变换,使三维运动问题转化为两维问题(轴向沟道运动)或一维问题(面沟道运动),从而大大简化了计算步骤,并以几种典型的相互作用势,讨论了沟道轻粒子在晶格中运动时束缚态之间的跃迁。用Moliere势计算出MeV电子在晶格轴向沟道中运动时发射与韧致辐射不同的量子辐射谱的特征,与实验结果相当符合。     

Cosmic gamma-ray background from structure formation in the intergalactic medium

The Universe is filled with a diffuse background of gamma-ray radiation, the origin of which remains one of the unsolved puzzles of cosmology. Less than one-quarter of the gamma-ray flux can be attributed to unresolved discrete sources, such as active galactic nuclei; the remainder appears to constitute a truly diffuse background. Here we show that the shock waves induced by gravity in the gas of the intergalactic medium, during the formation of large-scale structures like filaments and sheets of galaxies, produce a population of highly relativistic electrons. These electrons scatter a small fraction of the cosmic microwave background photons in the local Universe up to gamma-ray energies, thereby providing the gamma-ray background. The predicted diffuse flux agrees with the observed background across more than four orders of magnitude in photon energy, and the model predicts that the gamma-ray background, though generated locally, is isotropic to better than five per cent on angular scales larger than a degree. Moreover, the agreement between the predicted and observed background fluxes implies a mean cosmological density of baryons that is consistent with Big Bang nucleosynthesis.     

激光与薄膜靶作用产生X射线阿秒脉冲两种方案的比较

运用一维粒子模拟对经由相对论电子束汤姆逊散射来产生阿秒X射线的两种方案进行了研究。第一种是激光驱动薄膜靶产生相对论电子束以及经过汤姆逊散射产生阿秒X射线,运用倍频探测光的方案可得到更短波长X射线。第二种方案添加了反射厚靶,通过厚靶对驱动激光的反射来减小电子束的横向动量但让其通过,而探测脉冲经过电子束汤姆逊散射后的多普勒频移因子提高,得到的X射线波长也明显减小,光子能量达到1KeV,反射光频谱也明显优与第一种方案．     

Controlled injection and acceleration of electrons in plasma wakefields by colliding laser pulses

In laser-plasma-based accelerators, an intense laser pulse drives a large electric field (the wakefield) which accelerates particles to high energies in distances much shorter than in conventional accelerators. These high acceleration gradients, of a few hundreds of gigavolts per metre, hold the promise of compact high-energy particle accelerators. Recently, several experiments have shown that laser-plasma accelerators can produce high-quality electron beams, with quasi-monoenergetic energy distributions at the 100 MeV level. However, these beams do not have the stability and reproducibility that are required for applications. This is because the mechanism responsible for injecting electrons into the wakefield is based on highly nonlinear phenomena, and is therefore hard to control. Here we demonstrate that the injection and subsequent acceleration of electrons can be controlled by using a second laser pulse. The collision of the two laser pulses provides a pre-acceleration stage which provokes the injection of electrons into the wakefield. The experimental results show that the electron beams obtained in this manner are collimated (5 mrad divergence), monoenergetic (with energy spread <10 per cent), tuneable (between 15 and 250 MeV) and, most importantly, stable. In addition, the experimental observations are compatible with electron bunch durations shorter than 10 fs. We anticipate that this stable and compact electron source will have a strong impact on applications requiring short bunches, such as the femtolysis of water, or high stability, such as radiotherapy with high-energy electrons or radiography for materials science.     

光子的量子波动方程

给出外场中粒子的Lagrange函数及其Hamilton量的相对论表达式. 令静止质量m₀=0, 进一步给出光子的Hamilton量及光子在介质中的势能. 在此基础上, 给出自由和非自由光子的量子波动方程. 用该方程可研究光在光子晶体中的量子色散关系及量子透射等特性.     

An ultra-relativistic outflow from a neutron star accreting gas from a companion

Collimated relativistic outflows-also known as jets-are amongst the most energetic phenomena in the Universe. They are associated with supermassive black holes in distant active galactic nuclei, accreting stellar-mass black holes and neutron stars in binary systems and are believed to be responsible for gamma-ray bursts. The physics of these jets, however, remains something of a mystery in that their bulk velocities, compositions and energetics remain poorly determined. Here we report the discovery of an ultra-relativistic outflow from a neutron star accreting gas within a binary stellar system. The velocity of the outflow is comparable to the fastest-moving flows observed from active galactic nuclei, and its strength is modulated by the rate of accretion of material onto the neutron star. Shocks are energized further downstream in the flow, which are themselves moving at mildly relativistic bulk velocities and are the sites of the observed synchrotron emission from the jet. We conclude that the generation of highly relativistic outflows does not require properties that are unique to black holes, such as an event horizon.