# 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

## 物理代写|高能物理代写高能物理学代考|恒星天体物理学

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