河外伽马射线背景研究
发布时间：2018-07-31 07:35
【摘要】：河外伽马射线背景起源是一个重要但是没有解决的问题，它可能是由一些真正的弥散源所贡献，也可能是一些未被分解的点源所贡献。真正弥散源包括暗物质湮灭或衰变所辐射的伽马光子，或宇宙大尺度结构形成过程中激波所加速的高能粒子的辐射等。费米伽马射线太空望远镜上天后，尽管其灵敏度、角分辨率和有效面积相比以前的仪器有着革命性的提高，探测到了更多的河外点源，但是这些点源总的流量只是河外伽马射线背景的一小部分，距离直接分解河外伽马射线背景还有很大的距离。 图像叠加法是一种可以大大提高图像信噪比，从而充分利用现有数据的方法。我们利用此方法对一些可能的、还未被直接探测到的伽马射线点源样本叠加，然后利用最大似然法求其总流量，从而得出它们对河外伽马射线背景的贡献。 我们首先对AT20G样本进行叠加，发现其对河外伽马射线背景贡献为8.4%，小于由射电流量和伽马射线流量相关关系得到的比例。但是我们的方法更加直接。这表明由某类天体其它波段流量（或光度）和伽马射线流量（或光度）相关关系来得到其对河外伽马射线背景贡献有很大的不确定性。 然后我们对FIRST进行叠加，，此样本对河外伽马射线背景贡献为61.4%.但是其低射电流量的子样本的伽马射线流量不可忽略。考虑到FIRST样本为一流量限样本且在低流量处并不完备，则可以预期，如果此样本流量限更低且更加完备，则样本对河外伽马射线背景的贡献将会更大。但是具体贡献值则很难确定，这依赖于更暗源的数密度分布以及射电、伽马射线流量关系，然而两者目前都不确定。但是考虑到一些不能被FIRST示踪类型源，例如普通星系、射电宁静类星体等也可以贡献一部分河外伽马射线背景，可以认为点源即使不能完贡献全部也可也贡献绝大部分的河外伽马射线背景，标准天体物理模型可以解释全部的河外伽马射线背景起源。
[Abstract]:The origin of extragalactic gamma-ray background is an important but unsolved problem. It may be contributed by some real diffusing sources or some undecomposed point sources. The true dispersion sources include gamma photons emitted by the annihilation or decay of dark matter, or the radiation of high-energy particles accelerated by shock waves during the formation of the large-scale structure of the universe. The Fermi Gamma-Ray Space Telescope, though revolutionary in its sensitivity, angular resolution and effective area, detected more extragalactic point sources than previous instruments. However, the total flux of these point sources is only a small part of the background of the extragalactic gamma rays, and there is still a long way to go for the direct decomposition of the background of the gamma rays outside the river. Image superposition method is a method which can greatly improve the signal-to-noise ratio (SNR) of images and make full use of existing data. We use this method to superposition some possible gamma ray point source samples which have not been directly detected, and then use the maximum likelihood method to calculate the total flow rate, so as to obtain their contribution to the background of gamma rays outside the river. We first superposition the AT20G samples and find that their contribution to the background of gamma rays beyond the river is 8.4, which is less than the ratio obtained from the correlation between radio and gamma ray flows. But our approach is more straightforward. This indicates that there is great uncertainty about the contribution to the background of extragalactic gamma rays from the correlation between the other band flux (or luminosity) and the gamma ray flux (or photometry) of a certain type of celestial body. We then superimposed the FIRST, which contributed 61.4 to the extragalactic gamma ray background. But the gamma ray flux of the subsample of its low radio current can not be ignored. Considering that the FIRST sample is a flow-limited sample and is not complete at a low flow rate, it can be expected that if the flow limit of the sample is lower and more complete, the contribution of the sample to the off-river gamma-ray background will be greater. However, it is difficult to determine the specific contribution value, which depends on the number density distribution of the darker source and the relationship between radio and gamma ray flux, but both are uncertain at present. But considering that some types of sources that cannot be traced by FIRST, such as ordinary galaxies, radio tranquil quasars, and so on, can also contribute part of the off-river gamma-ray background, It can be considered that the point source can contribute most of the extragalactic gamma-ray background even if it can not complete the contribution, and the standard astrophysical model can explain the origin of all the extragalactic gamma-ray background.
【学位授予单位】：中国科学院研究生院（云南天文台）
【学位级别】：博士
【学位授予年份】：2013
【分类号】：P172.3
本文编号：2154878
[Abstract]:The origin of extragalactic gamma-ray background is an important but unsolved problem. It may be contributed by some real diffusing sources or some undecomposed point sources. The true dispersion sources include gamma photons emitted by the annihilation or decay of dark matter, or the radiation of high-energy particles accelerated by shock waves during the formation of the large-scale structure of the universe. The Fermi Gamma-Ray Space Telescope, though revolutionary in its sensitivity, angular resolution and effective area, detected more extragalactic point sources than previous instruments. However, the total flux of these point sources is only a small part of the background of the extragalactic gamma rays, and there is still a long way to go for the direct decomposition of the background of the gamma rays outside the river. Image superposition method is a method which can greatly improve the signal-to-noise ratio (SNR) of images and make full use of existing data. We use this method to superposition some possible gamma ray point source samples which have not been directly detected, and then use the maximum likelihood method to calculate the total flow rate, so as to obtain their contribution to the background of gamma rays outside the river. We first superposition the AT20G samples and find that their contribution to the background of gamma rays beyond the river is 8.4, which is less than the ratio obtained from the correlation between radio and gamma ray flows. But our approach is more straightforward. This indicates that there is great uncertainty about the contribution to the background of extragalactic gamma rays from the correlation between the other band flux (or luminosity) and the gamma ray flux (or photometry) of a certain type of celestial body. We then superimposed the FIRST, which contributed 61.4 to the extragalactic gamma ray background. But the gamma ray flux of the subsample of its low radio current can not be ignored. Considering that the FIRST sample is a flow-limited sample and is not complete at a low flow rate, it can be expected that if the flow limit of the sample is lower and more complete, the contribution of the sample to the off-river gamma-ray background will be greater. However, it is difficult to determine the specific contribution value, which depends on the number density distribution of the darker source and the relationship between radio and gamma ray flux, but both are uncertain at present. But considering that some types of sources that cannot be traced by FIRST, such as ordinary galaxies, radio tranquil quasars, and so on, can also contribute part of the off-river gamma-ray background, It can be considered that the point source can contribute most of the extragalactic gamma-ray background even if it can not complete the contribution, and the standard astrophysical model can explain the origin of all the extragalactic gamma-ray background.
【学位授予单位】：中国科学院研究生院（云南天文台）
【学位级别】：博士
【学位授予年份】：2013
【分类号】：P172.3
【参考文献】
相关期刊论文 前1条
1 曹新伍;活动星系核中的喷流形成[J];天文学进展;2002年01期
本文编号：2154878
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