利用ARGO实验寻找GRBs的本底研究

The background event study of search for GRBs with the ARGO experiment

位于西藏羊八井宇宙线观测站(海拔4300 m)的ARGO-YBJ实验具有高海拔、大视场、全覆盖特点,其阈能约几百个GeV,在探测高能GRBs方面具有独特的优势.ARGO-YBJ实验不能分辨光子和质子,要在大量的宇宙线事例中找出光子信号,就必须正确地估计背景事例率,这是寻找高能GRBs的关键.本文采用"等天顶角法"对ARGO实验中寻找GRBs的宇宙线本底进行了分析.由于地球的自转,天顶角随着时间的变化而变化.本文重点分析了长暴在其持续时间内天顶角的变化,从而更加准确地进行了本底估计.

ARGO-YBJ, located at the Yangbajing cosmic ray Observatory(4300 m a.s.l., Tibet, china), has a threshold energy of about several hundred GeVs. It is particular useful in searching for high energy GRBs because of its unique advantages of high altitude, wide field of view, and full coverage. ARGO-YBJ experiment can not distinguish between photons and protons. To find photon signals in a large number of cosmic ray events, we must correctly estimate the background event rate, which is the key to search for high-energy GRBs. In this paper, the "equi-zenith-angle" method is used to analyze the cosmic ray background of GRBs in ARGO experiment. Due to the rotation of the earth, the zenith angle varies with time. We focuses on the analysis of the change of zenith angle in the duration of the long GRBs,so that the background estimation is more accurate.