The sensitivity of EGRET to gamma-ray polarization     

John R. Mattox 《Experimental Astronomy》1991,2(2):75-84

A Monte Carlo simulation shows that the EGRET gamma-ray telescope aboard the GRO satellite does not have sufficient sensitivity to detect linear polarization, even for 100% polarized gamma-ray sources. This is confirmed by analysis of calibration data. Several data selection techniques suggested to enhance polarization sensitivity have been evaluated and found to not significantly improve sensitivity.NRC/NAS RESEARCH ASSOCIATE  相似文献   

SCATTERING PHASE MATRICES OF ICE CRYSTALS WITH HEXAGONAL PRISM AND TRIANGULAR PYRAMID FORM—A VECTOR RAY TRACING METHOD          下载免费PDF全文

Cai Qiming  Yang Ping 《Acta Meteorologica Sinica》1991,5(4):515-526

The work presented previously by the authors(Cai and Liou,1982)has been extended in this paper.By making use of our improved model the calculations on scattering phase matrices of hexagonal prismice crystals(HPIC)have been conducted for monodisperse and polydisperse systems.Compared with themodel of Cai and Liou,the required computational quantity is decreased by about two orders of magni-tude and the errors of results are less for the new model.Meanwhile,the scattering phase matrices of triangularpyramid ice crystals(TPIC)are also computed in the paper,and the comparison between the scatterings of thetwo forms of ice crystals is performed.  相似文献   

Brief history of ground-based very high energy gamma-ray astrophysics with atmospheric air Cherenkov telescopes     

《Astroparticle Physics》2014

The discovery of the Crab Nebula as the first source of TeV gamma rays in 1989, using the technique of ground-based imaging air Cherenkov telescope, has marked the birthday of observational gamma astronomy in very high energy range. The team led by Trevor Weekes, after twenty years of trial and error, success and misfortune, step-by-step improvements in both the technique and understanding of gamma shower discrimination methods, used the 10 m diameter telescope on Mount Hopkins in Arizona, and succeeded measuring a 9σ signal from the direction of Crab Nebula. As of today over 160 sources of gamma rays of very different types, of both galactic and extra-galactic origin, have been discovered due to this technique. This is a really fast evolving branch in science, rapidly improving our understanding of the most violent and energetic sources and processes in the sky.The study of these sources provides clues to many basic questions in astrophysics, astro-particle physics, physics of cosmic rays and cosmology. Today’s telescopes, despite the young age of the technique, offer a solid performance. The technique is still maturing, leading to the next generation large instrument. This article is devoted to outlining the milestones in a long history that step-by-step have made this technique emerge and have brought about today’s successful source hunting.  相似文献   

The H.E.S.S. central data acquisition system     

《Astroparticle Physics》2014

The High Energy Stereoscopic System (H.E.S.S.) is a system of Imaging Atmospheric Cherenkov Telescopes (IACTs) located in the Khomas Highland in Namibia. It measures cosmic gamma rays of very high energies (VHE; >100 GeV) using the Earth’s atmosphere as a calorimeter. The H.E.S.S. Array entered Phase II in September 2012 with the inauguration of a fifth telescope that is larger and more complex than the other four. This paper will give an overview of the current H.E.S.S. central data acquisition (DAQ) system with particular emphasis on the upgrades made to integrate the fifth telescope into the array. At first, the various requirements for the central DAQ are discussed then the general design principles employed to fulfil these requirements are described. Finally, the performance, stability and reliability of the H.E.S.S. central DAQ are presented. One of the major accomplishments is that less than 0.8% of observation time has been lost due to central DAQ problems since 2009.  相似文献   

两类γ暴的谱形和光变曲线的统计差异的K-S检验     

彭朝阳  覃一平 《天文研究与技术》2006,3(3):228-238

最近的研究表明：短γ射线暴（γ暴）的辐射特性和长γ暴的前两秒的辐射特征相似，这引发了对以前争论的问题，即：这两类暴是否是本质上相同的暴？本文主要对和γ暴谱形和光变曲线有关的两个量的分布进行了K—S检验。分析表明：这两类暴的分布是不同的，这和广为接受的两类γ暴事件产生于不同机制的观点是一致的。  相似文献   

Model of wind-generated ambient noise in stratified shallow water   总被引：1，自引：0，他引：1  

林建恒  高天赋 《中国海洋湖沼学报》2005,23(2):144-151

In order to build a rapid ocean ambient noise model adapted for a stratified shallow water, a hybrid model of normal mode method (for far field) and ray method (for near field) is suggested which combines the advantages of both methods. Since the near field of wind-generated noise is not sensitive to the sound speed profile, the sound speed profile is regarded as a constant; which makes the model rapid and accurate. The simulation results are in agreement with those of the wave model.  相似文献   

X Per新发射相的不寻常变化     

刘庆忠  杭恒荣 《天文学报》1997,38(4):434-440

对ＸＰｅｒ新发射相连续四年的光学光谱和近红外光度监测结果，ＸＰｅｒ近两年的变化不同寻常，主要表现以下两点：（１）尽管它的光学光度Ｖ星等只恢复至失去气壳前的亮度，但Ｈａ发射线等值宽度和近红外，Ｊ，Ｈ和Ｋ光度地超过了历史记录的最大值，分别达到了１６．３４Ａ和５．３＾ｍ，５．３＾ｍ和５．１＾ｍ，表明ＸＰｅｒ新发射相气南的密度和尺度较都大，（２）我们首次观测到ＸＰｅｒ近红外光度和Ｈα发射线等值宽度变化趋势  相似文献   

The effect of 3-D structure on Lg propagation patterns     

M. G. Bostock  B. L. N. Kennett 《Geophysical Journal International》1990,101(2):355-364

  相似文献   

Quasi-shear wave coupling in weakly anisotropic 3-D media   总被引：2，自引：0，他引：2  

R.T. Coates  C. H. Chapman 《Geophysical Journal International》1990,103(2):301-320

  相似文献   

Peculiarities of surface wave fields in laterally inhomogeneous media in the framework of ray theory     

T. B. Yanovskaya  Yu. V. Roslov 《Geophysical Journal International》1989,99(2):297-303

  相似文献