Corrected sidereal anisotropy for underground muons |
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Authors: | DB Swinson K Nagashima |
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Institution: | 1. Department of Physics and Astronomy, The University of New Mexico, 800 Yale N.E., Albuquerque, NM 87131, U.S.A.;2. Cosmic Ray Research Laboratory, Faculty of Science, Nagoya University, Chikusa-Ku, Nagoya, 464 Japan |
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Abstract: | Data from underground muon telescopes in New Mexico and Bolivia are analyzed in sidereal time and anti-sidereal time to study anisotropies in the rigidity range 20 GV to a few 100s of GV. Using both vertical and North- and South-pointing telescopes in both hemispheres, a latitude range of 70°N–50°S is covered. The distribution of cosmic rays in the inner heliosphere gives rise to a diurnal variation in anti-sidereal time, and also produces a spurious contribution to the anisotropy in sidereal time. It is shown that the anti-sidereal variation is of the P21 type, having opposite phase in the Northern and Southern Hemispheres, and maximum amplitude at mid latitudes. The anti-sidereal data are used to correct the sidereal data, using the Nagashima method (Nagashima, Sakakibara, Fenton and Humble, 1985); the resulting corrected sidereal vectors for Northern Hemisphere telescopes have their sidereal maxima close to 3 h sidereal time, in reasonable agreement with sidereal data at higher energies from small air showers. The Nagashima correction also appears to eliminate effects due to the reversal of the Sun's polar magnetic field which show up in the unconnected sidereal data, and which also remain in corrected data using an alternative correction. |
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