Arrival directions of cosmic-ray air showers from the equatorial sky

Abstract

The celestial arrival directions of over 100 000 showers with sizes greater than 10⁵ particles have been determined by fast timing in observations at an altitude of 2034 m. The observations covered a band of declinations from -30° to +50° with an angular resolution of 4°, and they extended a survey begun in an earlier experiment that covered the northern sky. As in the earlier experiment no significant deviation from isotropy was found. The atmospheric attenuation of the shower intensity was determined from the zenith angle distribution, and also from a comparison of the absolute shower intensity at 2034 m and at sea level. Within an experimental uncertainty of about 5%, both methods yield an exponential attenuation length consistent with the value of 107 g cm^-2 previously found at sea level. The absolute intensity of showers with more than 10⁵ particles at 2034 m was found to be (1.11±0.30)×10^-9 cm^-2 sec^-1 sr^-1.