A sky survey for flaring point sources emitting high energy gamma rays has been performed with the L 3+ C underground muon spectrometer at LEP, CERN. Data were collected from mid July to October 1999 and from April to November 2000. No signal excesses in any direction have been found with muons above 20, 30, 50 and 100 GeV within one day and longer time windows. The steady muon flux sensitivity is of the order of a few times 10-9 cm-2 s-1 for muon energies above 20 GeV, and between 2 × 10-11 and 5 × 10-10 cm -2 s -1 for muon energies above 20 GeV depending on the source position.
Time variations in the deep underground muon flux