【作者】 周勋秀；

【导师】 贾焕玉；

【作者基本信息】 西南交通大学 ， 电磁场与微波技术， 2009， 博士

【摘要】 γ射线暴是来自宇宙空间的γ射线在短时间内猛烈爆发的一种现象。自1967年美国的军事卫星Vela首次发现这种现象以来,γ射线暴一直是天文学界最神秘的现象之一。为此,许多卫星实验和地面实验投入到了γ射线暴的研究工作中。到目前为止,卫星实验已观测到4000多个γ射线暴,其理论研究也获得了一些突破性的进展,但有关γ射线暴的一些基本问题(如γ射线暴的起源是什么?γ射线暴的产生机制是什么?)还存在激烈的争论。40多年来,探测到的γ射线暴都在keV-MeV能区,而EGRET和Fermi也只观测到几个有GeV光子辐射的γ射线暴。为得到γ射线暴不同能段的完整图像,探测GeV-TeV能区的γ射线辐射是非常重要的；同时观测GeV-TeV能区的γ射线暴,可为其起源和产生机制带来重要的信息,并对γ射线暴的理论模型加以检验。位于西藏羊八井的ARGO实验,由于其覆盖率大、视场宽、观测周期长、探测阈能低等优点,使得ARGO实验在探测γ射线暴方面比目前其它地面宇宙线观测实验有着更高的灵敏度。本文模拟计算了ARGO实验探测E>10GeVγ射线暴的最低流强,得到对红移小(z<0.5)、流强大(大于10-5erg.cm-2.s-1)的γ射线暴,ARGO实验有一定的灵敏度,这表明利用ARGO实验寻找γ射线暴不是不可能的。本文利用ARGO实验在2006年6月—2008年12月期间采集的数据,与进入ARGO视场(在羊八井观测站的天项角θ<45°)的32个卫星γ射线暴,在GeV-TeV能区进行了伴随γ射线暴的符合寻找。在利用Shower数据寻找E＞10GeV的伴随暴时,显著性最高的是与GRB081102B符合寻找中的一个事例团,其作为本底涨落的几率为5.2×10-7,相当于高斯分布的4.88σ；有趣的是,在利用Scaler数据寻找E＞1GeV的伴随暴时,显著性最高的也是与GRB081102B符合寻找中的一次试验,其显著性为5.34σ。文中对Shower数据与Scaler数据寻找γ射线暴的结果进行了符合、讨论。遗憾的是,在考虑试验次数后,文中所得显著性较高事例团的超出都不足以认定为γ射线暴。考虑河外背景的吸收效应后,估算了在95%置信水平下,ARGO实验探测γ射线暴所需要的流强上限(文中考虑了γ射线暴的持续时间、能谱指数、红移、天顶角等因素的影响)。当γ射线暴的能谱指数α取2.5、红移z取0时,流强上限可低达10-6erg.cm-2。更多还原

【Abstract】 Gamma-ray bursts (GRBs) are the brightest explosions of gamma rays coming from the universe in a short period of time. Since their discovery by Vela satellite in 1967, gamma-ray bursts have remained one of the most enigmatic astronomical phenomena. Therefore, gamma-ray bursts have been studied by several satellite experiments and ground-based experiments.Upto now, more than four thousands of GRBs have been observed by satellite experiments.At the same time,theoretical studies are going on very actively. Though much progress has been achieved from both experimental and theoretical efforts, lots of basic questions such as the origin and the emission mechanism of GRBs still remain unresolved.However, most up-to-date known GRBs were observed in energy range from keV to MeV and the only several GRBs were detected by EGRET and Fermi which emitted GeV photons. In order to understand the complete picture of the process, it is important to detect the GeV-TeV emissions from GRBs. At the same time, searching for GeV-TeV GRBs is very important to give some information on the origin and the emission mechanism of GRBs, and also give constrain on the models of GRBs.The ARGO experiment, located at Yangbajing, Tibet, China,have many advantages such as full coverage, wide field of view, high duty cycle and the lowest threshold energy. So, ARGO experiment is expected to have higher sensitivity in detecting GRBs than other ground-based experiments. In this work, we study the ARGO sensitivity in detecting GRBs with photon energies greater than 10 GeV. If the redshift of GRBs are less than 0.5 and the f luence are more than 10-5 erg. cm-2. s-1, ARGO will be sensitive enough to discover them.Searching for GeV-TeV GRBs coincidence with satellite GRBs data is carried out by using the ARGO Shower mode data and Scaler mode data. Between June 2006 and December 2008,32 GRBs detected by satellites occurred within the field view of ARGO(zenith angleθ<45°). Using the Shower mode data, the lowest chance probability (Pb) is 5.2X 10-7 which is related with GRB081102B. Using the Scaler mode data, the highest significance is 5.34σwhich is also related with GRB081102B. The results are discussed in text.After considering the number of trials, no significant GeV-TeV GRBs was observed. The EBL absorption was considered, then the fluence upper limits which depends on GRBs’time duration, spectral index, redshift and the zenith angle at the observation were estimated at the 95% confidence level by Monte Carlo simulation. If the redshift z=0. and the spectral index a=2.5,the fluence upper limits for ARGO to detect E>10GeV GRBs reach values as low as 10-6erg. cm-2更多还原