OBSERVATION OF MUON EXCESS AT GROUND LEVEL IN RELATION TO GAMMA-RAY BURSTS DETECTED FROM SPACE

In this paper we examine the possibility of the ground observation of the gigaelectronvolt counterparts associated with the Monitor of All-sky X-ray Image transient event (trigger 58072727) and the Swift GRB140512A event. In both cases, there was a muon excess with a statistical significance above 4σ. The coordinates of the events were located in the field of view (FOV) of the Tupi muon telescopes at the time of the occurrence. Since 2013 August, the Tupi experiment has been operating a new extended array of five muon telescopes, located at ground level at (22°.9S, 43°.2W, 3 m above sea level). This location coincides with the South Atlantic Anomaly central region. We consider a hypothesis that the muon excess could be due to photonuclear reactions in the Earth's atmosphere induced by gamma rays with energies above 10 GeV. We describe a data analysis for candidate events identified by internally triggered (by the Tupi experiment) as well as untriggered (dependent on external observations) modes of search. In light of the Fermi LAT (>100 MeV) gamma-ray bursts (GRBs) catalog, we examine the possibility of the ground observation of similar transient events within the FOV of the extended Tupi array and perform a systematic analysis of the Tupi data. Using a Monte Carlo simulation, we discuss the experimental conditions that allow the detection of signals from GRBs at ground level.