摘要
We study the sidereal and solar time modulation of multi-TeV cosmic rays using the east-west method with Tibet air shower array data taken from November 1999 to December 2008. The statistics are twice the amount used in our previous paper. In this analysis, the amplitude of the observed sidereal time modulation is about 0.1%, and the modulation shows an excess from about 4 to 7 hours and a deficit around 12 hours in local sidereal time. The sidereal time modulation has a weak dependence on the primary energy of the cosmic rays. However, the solar time modulation shows a large energy dependence. We find that the solar time modulation is fairly consistent with the prediction of the Compton-Getting effect for high-energy samples （6.2TeV and 12.0TeV）, but exceeds the prediction for the low-energy sample （4.0TeV）. Such a discrepancy may be due to the solar modulation or the characteristics of the experimental device in the near threshold energy.
We study the sidereal and solar time modulation of multi-TeV cosmic rays using the east-west method with Tibet air shower array data taken from November 1999 to December 2008. The statistics are twice the amount used in our previous paper. In this analysis, the amplitude of the observed sidereal time modulation is about 0.1%, and the modulation shows an excess from about 4 to 7 hours and a deficit around 12 hours in local sidereal time. The sidereal time modulation has a weak dependence on the primary energy of the cosmic rays. However, the solar time modulation shows a large energy dependence. We find that the solar time modulation is fairly consistent with the prediction of the Compton-Getting effect for high-energy samples （6.2TeV and 12.0TeV）, but exceeds the prediction for the low-energy sample （4.0TeV）. Such a discrepancy may be due to the solar modulation or the characteristics of the experimental device in the near threshold energy.
基金
Supported by Natural Science Foundation of Shandong Province of China (ZR2009AM003)
National Natural Science Foundation of China
Chinese Academy of Sciences and Ministry of Education of China
Innovation Foundation of Shandong Agriculture University(23665)
