ANGULAR-DISTRIBUTION OF COSMIC-RAYS AT THE BOUNDARY OF THE HELIOSPHERE

Measurements of the sidereal daily variation of the muon intensity at a depth of 60 m.w.e. have been carried out in London using telescopes inclined at 70° to the zenith for the period 1972 to the present. The direction of maximum sensitivity for these telescopes lies in the Earth's equatorial plane and the asymptotic directions of look at the boundary of the heliosphere have been determined by integrating the equation of motion of the primary particles in a model interplanetary magnetic field. In this way the measured sidereal variation can be related to the cosmic ray intensity distribution in interstellar space. It is shown that the observational data are consistent with an axially symmetric intensity distribution of the form ΔI = 0.09 (1 + cos α) % where ΔI is the direction from the mean intensity and α is measured from the direction of maximum intensity which lies at 1Π = 250° bΠ = -60°. The most likely interpretation of this result is that the axis of this distribution corresponds to the local direction of the interstellar magnetic field and that the cosmic rays have a bulk streaming motion of 65±15 km s-1 along the field direction. © 1979.