银河系宇宙线相互作用的GALPROP模拟浅析

宇宙线从源产生后传播到地球要和星际介质、磁场和辐射场等发生相互作用,它把天体物理源、星际空间环境等因素都联系起来,是获取天体物理信息的重要手段之一。GALPROP是一个数值求解宇宙线传播的程序包,包含了宇宙线传播中的各种物理过程,它能在统一的模型框架下模拟宇宙线的相互作用,尽可能利用真实的天体物理信息,达到模拟银河系宇宙线相互作用的真实情况。     

行星际空间中激波加速的宇宙线粒子能谱的解析表式

本文从基本的对流扩散方程出发,在空间扩散系数随动量和位置以及太阳风速随位矢变化的一般假定下,获得了行星际空间中激波加速的宇宙线能谱的解析表式。     

气球宇宙线核同位素观测实验

1 引言宇宙线天体物理研究来自宇宙深处的高能粒子,初级宇宙线核成分观测是其中的一个重要课题.初级核成分的观测之所以重要,是因为宇宙线源通过核反应产生大量重核,而在向外传播过程中要与星际物质碰撞产生各种轻核(Li,Be,B 等),测定地球附近的宇宙线核成分,可以帮助人们弄清宇宙线在银河系中的传播机制,弄清宇宙线源内部的核成分和产生机制.芝加哥大学在这一研究领域目前处于领先地位,HEIDI(High Energy Isotope     

宇宙线研究相关的伽马射线天文（英文）

宇宙线是星际介质中最重要的成分之一，然而其起源至今成谜。宇宙线在星际湍动磁场中的扩散在很大程度上抹去了宇宙线加速源的分布信息。而宇宙线扩散过程的能量相关性又改变了宇宙线的初始能谱。因此，伽马射线，作为宇宙线与星际介质中气体和光子相互作用产生的次级产物，能提供更多的关于宇宙线起源的信息。更具体的，与气体分布成协的弥散伽马射线可用来研究宇宙线的分布，而离散的伽马射线源能用来研究单独的宇宙线加速源。本文介绍了该领域的现状和未来前景。     

10TeV宇宙线的太阳阴影研究

利用１９９５年１０月至１９９７年９月间西藏空气簇射阵列采集到的数据，再一次观测到了１０ＴｅＶ宇宙线的太阳阴影；仔细分析了１９９０年６月至１９９７年９月间观测到的１０ＴｅＶ宇宙线的太阳阴影位置，对其位置的偏移及变化行为给出了定性的解释；结合相同时期的太阳表面平均磁场强度，进一步证实了日影偏离度与太阳平均磁场的关联；利用较为完整的宇宙线成分测量数据，对日影偏离度与太阳平均磁场强度间的定量关系作了成分上的修正．     

LHAASO与宇宙线起源

宇宙线的能谱延展到超过10¹⁵电子伏特(PeV)的能段,这表明银河系中存在超高能的宇宙线加速源.而近期的甚高能伽马射线观测表明,长期以来被认为是主要宇宙线加速源的超新星遗迹很难把宇宙线加速到超高能.因此,寻找超高能(PeV)宇宙线加速源是宇宙线起源研究中的核心问题.其中一个最直接的方法就是寻找加速源附近宇宙线与星际气体相互作用产生的超高能伽马射线辐射.我国的高海拔宇宙线观测站(LHAASO),由于其在超高能伽马射线能段世界领先的灵敏度,成为这一研究的理想工具.LHAASO半阵列建成后一年之内,已经在银盘上观测到了十二个超高能伽马射线源,在这一领域取得了突破性的进展.本文将介绍这些已得到的观测结果,并对LHAASO全阵列建成后可能的新进展进行展望.     

非磁暴期间银河宇宙线强度的小波分析

利用小波分析分析了非磁暴期间几种情况下宇宙线强度的变化,结果表明,只有行星际较平静时银河宇宙线强度的周日变化才比较明显和稳定.不同年份,地磁静日银河宇宙线日波峰值取值的地方时可能不同.当行星际出现扰动但没有出现磁暴时,银河宇宙线的日波也会出现变化,即日波幅度会出现减弱或增强,因此,仅利用银河宇宙线的日波变化情况不能作为地磁暴前兆的判据,只能作为行星际扰动的判据.     

银河系宇宙线传播模型探讨

宇宙线从源产生后传播到地球要和星际介质、磁场和辐射场等发生相互作用,它把天体物理源、星际空间环境等因素都联系起来,是获取天体物理信息的重要手段之一,因此探索宇宙线的传播模式是非常有意义的.     

流管几何对低速太阳风alpha粒子丰度的影响

建立了离子回旋共振机制驱动的一维三元(电子、质子、alpha粒子)低速太阳风流管模型,重点分析流管参数对alpha粒子丰度(定义为alpha粒子与质子数密度之比)的影响.流管几何形式与有关观测数据分析及二维太阳风模型的计算结果相一致.与以往研究相符,在太阳附近alpha粒子的丰度先增加(可超过冕底丰度的1~5倍),尔后迅速降至行星际空间中的平均观测数值.alpha粒子丰度极大值αmax在大约1.5~1.7 Rs范围内获得,具体数值主要取决于流管的几何参数包括冕流尖点的高度与相应膨胀因子的极大值:尖点越靠近太阳、极大膨胀因子越大,则αmax越大.但是这两个参数对于行星际空间中alpha粒子的特征影响不大;而合理地改变流管在远处的膨胀因子,可定性解释低年低速太阳风中alpha粒子的平均丰度与太阳风速度正相关的观测现象.     

米波射电观测研究银河宇宙线的分布和起源

100多年来,银河宇宙线的起源,传播,空间分布一直是宇宙线的研究重点之一,至今虽有巨大进展但仍远没有完全明白.近年来,射电,光学,X-ray和γ-ray的联合观测对我们了解银河宇宙线起到了重要的推动作用.它们已经给出的众多证据表明银河宇宙线很有可能主要起源于超新星遗迹的扩散激波加速.对高灵敏度Fermi银河弥散γ-ray数据的分析,使得我们对宇宙线在银河系内分布和组成的认识进一步加深.米波射电观测将有可能在银河宇宙线的空间分布和传播(通过电离氢区和行星状星云的吸收观测,高灵敏度高分辨率米波射电巡天),宇宙线的起源(超新星遗迹激波区域的观测,河外点源和脉冲星的闪烁,散射观测,Te Vγ-ray源在低能端的对应体的搜寻)方面起到重要的作用.     

Discovery of very-high-energy gamma-rays from the Galactic Centre ridge

The source of Galactic cosmic rays (with energies up to 10(15) eV) remains unclear, although it is widely believed that they originate in the shock waves of expanding supernova remnants. At present the best way to investigate their acceleration and propagation is by observing the gamma-rays produced when cosmic rays interact with interstellar gas. Here we report observations of an extended region of very-high-energy (> 10(11) eV) gamma-ray emission correlated spatially with a complex of giant molecular clouds in the central 200 parsecs of the Milky Way. The hardness of the gamma-ray spectrum and the conditions in those molecular clouds indicate that the cosmic rays giving rise to the gamma-rays are likely to be protons and nuclei rather than electrons. The energy associated with the cosmic rays could have come from a single supernova explosion around 10(4) years ago.     

Galactic cosmic ray origin of Li, Be and B in stars

A study of the implications of the hypothesis that high energy processes involving cosmic rays acting on the interstellar medium are the sources of the elements Li, Be and B present in stellar atmospheres and in the solar system.     

Voyager 1 exited the solar wind at a distance of approximately 85 Au from the Sun

The outer limit of the Solar System is often considered to be at the distance from the Sun where the solar wind changes from supersonic to subsonic flow. Theory predicts that a termination shock marks this boundary, with locations ranging from a few to over 100 au (1 Au approximately 1.5 x 10(8) km, the distance from Earth to the Sun). 'Pick-up ions' that originate as interstellar neutral atoms should be accelerated to tens of MeV at the termination shock, generating anomalous cosmic rays. Here we report a large increase in the intensity of energetic particles in the outer heliosphere, as measured by an instrument on the Voyager 1 spacecraft. We argue that the spacecraft exited the supersonic solar wind and passed into the subsonic region (possibly beyond the termination shock) on about 1 August 2002 at a distance of approximately 85 Au (heliolatitude approximately 34 degrees N), then re-entered the supersonic solar wind about 200 days later at approximately 87 au from the Sun. We show that the composition of the ions accelerated at the putative termination shock is that of anomalous cosmic rays and of interstellar pick-up ions.     

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.     

Extremely fast acceleration of cosmic rays in a supernova remnant

Galactic cosmic rays (CRs) are widely believed to be accelerated by shock waves associated with the expansion of supernova ejecta into the interstellar medium. A key issue in this long-standing conjecture is a theoretical prediction that the interstellar magnetic field can be substantially amplified at the shock of a young supernova remnant (SNR) through magnetohydrodynamic waves generated by cosmic rays. Here we report a discovery of the brightening and decay of X-ray hot spots in the shell of the SNR RX J1713.7-3946 on a one-year timescale. This rapid variability shows that the X-rays are produced by ultrarelativistic electrons through a synchrotron process and that electron acceleration does indeed take place in a strongly magnetized environment, indicating amplification of the magnetic field by a factor of more than 100. The X-ray variability also implies that we have witnessed the ongoing shock-acceleration of electrons in real time. Independently, broadband X-ray spectrometric measurements of RX J1713.7-3946 indicate that electron acceleration proceeds in the most effective ('Bohm-diffusion') regime. Taken together, these two results provide a strong argument for acceleration of protons and nuclei to energies of 1 PeV (10(15) eV) and beyond in young supernova remnants.     

反质子的探索

作者用高能加速器实验和宇宙线实验总结出来的规律计算了宇宙空间中次级反质子的流强与质子流强之比。把计算结果与实验数据比较,发现1.在E>1.3GeV能区,原初反物质不可能存在;2.在1.1GeV<E<1.3GeV能区,宇宙空间中很可能存在反物质。     

The knee at cosmic ray spectra is explained due to interactions at the sources

In the paper the authors from the Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences in Beijing proposed a new model trying to explain the knee at cosmic ray spectra. The knee kept as a puzzle in cosmic ray physics for nearly half a century. The work was inspired by the recent observation of anomalous excess of electrons and positrons in cosmic rays. The work tries to explain the knee and the electron/positron excess in a single model.......     

追踪宇宙“信使”冲击世纪谜题——高海拔宇宙线观测站简介

 宇宙线的研究具有悠久的历史,取得了许多划时代的发现性成果。但是人类对宇宙线的起源、加速和传播等问题仍存在诸多疑惑。大型高海拔空气簇射观测站（LHAASO）独具高海拔和大规模优势,计划利用多种探测手段开展联合观测,大幅提升对伽马和宇宙线粒子的鉴别能力。LHAASO有望获得史上最高的伽玛探测灵敏度,并在很宽的能量范围内精确测量宇宙线能谱,为宇宙线物理、高能天体物理、宇宙学和新物理学规律研究做出贡献。介绍了LHAASO的探测器结构、性能优势和科学目标。     

Newly synthesized lithium in the interstellar medium

Astronomical observations of elemental and isotopic abundances provide the means to determine the source of elements and to reveal their evolutionary pathways since the formation of the Galaxy some 15 billion years ago. The abundance of lithium is particularly interesting because, although some of it is thought to be primordial, most results from spallation reactions (in which Galactic cosmic rays break apart larger nuclei in the interstellar medium). Spallation reactions are crucial for the production of other light elements, such as beryllium and boron, so observations of lithium isotopic abundances can be used to test model predictions for light-element synthesis in general. Here we report observations of 7Li and 6Li abundances in several interstellar clouds lying in the direction of the star o Persei. We find the abundance ratio 7Li/6Li to be about 2, which is significantly lower than the average Solar System value of 12.3 (refs 6, 7). An abundance ratio of 2 is clear evidence that the observed lithium must have resulted entirely from spallation, confirming a basic tenet of light-element synthesis. The total lithium abundance, however, is not enhanced as expected.     

An asymmetric solar wind termination shock

Voyager 2 crossed the solar wind termination shock at 83.7 au in the southern hemisphere, approximately 10 au closer to the Sun than found by Voyager 1 in the north. This asymmetry could indicate an asymmetric pressure from an interstellar magnetic field, from transient-induced shock motion, or from the solar wind dynamic pressure. Here we report that the intensity of 4-5 MeV protons accelerated by the shock near Voyager 2 was three times that observed concurrently by Voyager 1, indicating differences in the shock at the two locations. (Companion papers report on the plasma, magnetic field, plasma-wave and lower energy particle observations at the shock.) Voyager 2 did not find the source of anomalous cosmic rays at the shock, suggesting that the source is elsewhere on the shock or in the heliosheath. The small intensity gradient of Galactic cosmic ray helium indicates that either the gradient is further out in the heliosheath or the local interstellar Galactic cosmic ray intensity is lower than expected.