【作者】 周明；

【导师】 王建成；

【作者基本信息】 中国科学院研究生院（云南天文台） ， 天体物理， 2013， 博士

【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。更多还原

【Abstract】 The origin of the extragalactic gamma-ray background (EGB) is one of thefundamental unsolved problems in astrophysics. The EGB could originate fromeither truly difuse processes or from unresolved point sources. Truly difuseemission can arise from some processes such as the annihilation of dark matter,the emission of high energy particles accelerated by intergalactic shocks which areproduced during large scale structure formation, etc. Now, only a small fractionof the extragalactic gamma-ray emission is resolved into point sources.For a sample of possible γ-ray point sources that have not been detected bythe Fermi due to their faint fuxes or soft spectra, we can stack a large numberof them to improve the statistics. If their fuxes are not too faint, we can derivetheir mean fux and photon index by a maximum likelihood method.Applying the method to the Australia Telescope20GHz Survey sourcesundetected by the LAT, we found that these sources contribute about8.4%ofthe EGB. which are much smaller than the result (17%) of Ghirlanda et al.[51].But our method is more directly.Then, we use the method of image stacking to FIRST sources, and fnd thatthe FIRST sources undetected by the LAT can contribute about61.4%of theEGB. Considering the fux limit and incompleteness of the sample at the faintlimit, and the contribution of the fainter radio subsample to the EGB cannotbe ignored, we think that the point sources must contribute most of the EGB.The main contributor of the EGB maybe blazars, non-blazars AGNs, starburstgalaxies, and the sources cannot traced by the FIRST survey (including normalgalaxies and radio-quiet AGNs). Even though it is difcult to derive the fractionof each population contributing to the EGB using ours method alone, it is clearthat standard astrophysical scenarios can be invoked to explain the EGB.更多还原