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物理代写|高能物理代写High Energy Physics代考|Space-Based Instruments for X-Ray and γ-Ray Detection

The beginning of X-ray Astrophysics (the “softest” photons in the high energy region) had to await the development of space technology. Shortly after the launch of Sputnik in 1957, a group of scientists led by Riccardo Giacconi launched an X-ray detector on board an Aerobee 150 rocket and discovered the first X-ray source outside the Solar System, called Sco X-1. The angular resolution was so poor (worse than $20^{\circ}$ ) that it took time to identify the “spot” in X-rays with the constellation of Scorpius. Today we know that it is a neutron star with a low mass companion (LMXB), the first example showing how the sky is populated with high energy sources. A chronology of the most relevant missions can be found at the website [6].

A few years later in 1970 , the first satellite dedicated to X-ray sky exploration was launched. This was the Uhuru mission (meaning “freedom” in Swahili), with an effective area of only $0.084 \mathrm{~m}^2$ and coverage in the $2-20 \mathrm{keV}$ band, capable of a spatial resolution of about $0.5^{\circ}$. Uhuru identified more than 300 sources, among them Cyg X-1, the first black hole candidate in our galaxy. Over time, several missions have been launched, some of them still in operation, and the exploration of X-ray sources has continued on a sustained basis. Table $3.1$ shows some of the most important space missions in X-ray astrophysics, along with their most important features (collecting area, spatial resolution, and energy band).

As previously mentioned, one must use scintillators to study still higher energies. The Compton effect described above was the basis of the COMPTEL instrument, containing liquid scintillators above a $\mathrm{NaI}$ crystal. The successive interactions of the incident photons until they are finally absorbed can be used to determine the direction of their arrival without having to actually focus them in the conventional sense. The coded mask technique was developed to improve the spatial resolution, which is made much more difficult by the fact that gamma rays cannot be focused. This is an advanced variant of the camera obscura used in the Renaissance.

物理代写|高能物理代写High Energy Physics代考|Stellar Astrophysics

The nature of the observed stars has been a subject of discussion and speculation since the early days of civilization. Atomists Leucippus and Democritus thought that the Milky Way was made of stars, which they considered too small to be distinguished from one another. By the time of the Indian mathematician Aryabhata (5th century A.D.), there existed in the East the notion that stars were, in fact, other suns. It would have been immediately obvious that they would have to be at enormous distances for this hypothesis to make sense. Other important speculations were formulated in the West. For example, in Giordano Bruno’s writings, not only were the stars identified as distant suns, but inhabited planetary systems accompanied them, putting the author on a direct collision course with the Roman Catholic Church. What is certain is that it was only in the early 19th century, with the works of W. Herschel and J. von Fraunhofer, that the star = Sun identification was shown to be correct: the absorption lines of several nearby stars were observed, revealing their kinship with the lines observed in the solar spectrum. This Chapter addesses the construction of stellar models and the important features of Stellar Evolution till the final stages leading to explosions/compact object formation.

Although the nature of stars remained for many centuries on a speculative plane. scientists from Classical Antiquity devoted themselves to their study. The first catalog of stars created in the West was authored by the mathematician and astronomer Hipparchus, and contained some 850 stars observable by naked eye, as reproduced in Ptolemy’s Almagest. Hipparchus and other later astronomers also noticed the differences in brightness of the stars, and especially in their colors (Fig. 4.1). These ancient observations and those recorded after the invention of the telescope in the early 17th century led directly to the basic questions of stellar Astrophysics that will be the subject of our discussion: Are stars “eternal”? What is their internal constitution? How can these questions be linked with available observations? The enormous development of the theory of Stellar Evolution throughout the 20th century and the state of the art in this field will occupy the rest of this chapter and part of the following chapters.

物理代写|高能物理代写High Energy Physics代考|PHY-813

物理代写|高能物理代写高能物理代考|天基x射线和γ射线探测仪器

. x射线探测仪器


x射线天体物理学(高能区域“最柔软”的光子)的开始必须等待空间技术的发展。1957年斯普特尼克发射后不久,由里卡多·贾科尼(Riccardo Giacconi)领导的一组科学家在Aerobee 150火箭上发射了x射线探测器,发现了太阳系外的第一个x射线源,名为Sco X-1。角度分辨率非常差(比$20^{\circ}$还差),以至于花了很长时间才能在x射线中识别天蝎座的“光点”。今天我们知道它是一颗中子星,伴星质量很低(LMXB),这是第一个表明天空中充满高能量源的例子。最相关的任务年表可在[6]网站上找到


几年后的1970年,第一颗专门用于x射线天空探测的卫星发射了。这是Uhuru任务(在斯瓦希里语中是“自由”的意思),有效区域仅为$0.084 \mathrm{~m}^2$,覆盖$2-20 \mathrm{keV}$波段,空间分辨率约为$0.5^{\circ}$。乌胡鲁发现了300多个黑洞源,其中包括Cyg X-1,这是我们星系中第一个黑洞候选星系。随着时间的推移,已经发起了若干次任务,其中一些仍在执行,x射线源的探索一直在持续进行。表$3.1$显示了x射线天体物理学中一些最重要的空间任务,以及它们最重要的特征(收集面积、空间分辨率和能带)


如前所述,人们必须使用闪烁体来研究更高的能量。上面描述的康普顿效应是COMPTEL仪器的基础,在$\mathrm{NaI}$晶体上包含液体闪烁体。入射光子之间的连续相互作用,直到它们最终被吸收,可以用来确定它们到达的方向,而不必像传统意义上那样实际聚焦它们。编码掩模技术是为了提高空间分辨率而开发的,由于伽马射线无法聚焦,这使得空间分辨率变得更加困难。这是文艺复兴时期使用的暗箱的高级改进型。

物理代写|高能物理代写高能物理学代考|恒星天体物理学


自文明早期以来,对观测到的恒星的性质一直是讨论和推测的主题。原子学家琉基普斯和德谟克利特认为银河系是由恒星组成的,他们认为这些恒星太小,无法相互区分。在印度数学家阿雅巴塔(公元5世纪)的时代,东方有一种观念,认为恒星实际上是其他的太阳。很明显,要使这个假设成立,它们必须有巨大的距离。其他重要的推测是在西方提出的。例如,在佐丹诺·布鲁诺的作品中,这些恒星不仅被认为是遥远的太阳,而且还有有人居住的行星系统伴随着它们,这使作者与罗马天主教会直接发生了冲突。可以肯定的是,直到19世纪初,随着赫舍尔和夫琅和费的工作,恒星=太阳的区分才被证明是正确的:观测到几颗附近恒星的吸收线,揭示了它们与太阳光谱中观测到的线的亲缘关系。本章阐述了恒星模型的构建和恒星演化的重要特征,直到最后阶段导致爆炸/致密物体的形成


虽然许多世纪以来,恒星的性质一直停留在一个推测的层面上。古代的科学家们致力于他们的研究。西方最早的恒星目录是由数学家和天文学家希帕尔库斯撰写的,其中包括肉眼可观测到的约850颗恒星,如托勒密的《全集》中所复制的那样。希帕克斯和其他后来的天文学家也注意到了恒星亮度的差异,特别是它们的颜色(图4.1)。这些古老的观测和17世纪早期望远镜发明之后的记录直接导致了恒星天体物理学的基本问题,这将是我们讨论的主题:恒星是“永恒的”吗?它们的内部结构是什么?如何将这些问题与现有的观察结果联系起来?整个20世纪恒星演化理论的巨大发展和这一领域的技术水平将占据本章其余部分和以下几章的部分内容

物理代写|高能物理代写High Energy Physics代考

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