Search for UHE emission from 4U0115+63

We report here the preliminary results of our observations of the sporadic X‐binary system 4U0115+63. The CYGNUS air shower array has been collecting data since April 1986. No significant excess is seen from the direction of this source, nor any correlation with its 24‐day orbital period. A 90% confidence‐level upper limit on the flux from 4U0115+63 is 2.8×10−13 cm−2 s−1 above 50 TeV. This flux limit is considerably lower than those reported by other UHE experiments. Search for periodicity at the neutron star frequency is in progress.