An underground search for an excess muon flux from the direction of Cygnus X-3

During the period July, 1987 through March, 1988 (lifetime 0.5 year) an array of 128 proportional wire modules, arranged in two planes (each of two crossed layers) separated by 10 m, and with effective overlap areas of 35 m2, was operated as an underground muon detector. The detector is located at a depth of 2100 meters of water equivalent in northern Minnesota (92.2 degree W. 47.4 degree N). The response time for the proportional tubes is 1 μs and the overall angular resolution is 2 degree. Absolute timing information (∼1 ms) was available for most of the 250,000 recorded triggers. A sample of the total data consisting of 103,000 reconstructed, single muon tracks, was used to search for an excess muon flux from the direction of the astronomical point source, Cygnus X-3. The authors reports an integrated excess flux from that direction of (6 ± 2) x 10-11 cm-2s-1. The vertical muon flux was also measured and found to be (1.2 ± 0.3) x 10-3 m-2s-1 sterad-1