An alternative method for determining the energy of hybrid events at the Pierre Auger Observatory

THE PIERRE AUGER COLLABORATION (AUTOR 434 DE 474); M. TUEROS

Lodz, Polonia

Conferencia; 31st International Cosmic Ray Conference; 2009

An important feature of the Pierre Auger Observatory is the detection of hybrid events; i.e.,extensive air showers simultaneously detected with atleast one water-Cherenkov detector (surface detector) and one fluorescence telescope. Here we describe an alternative method of estimating the energy of these events. The shower axis is determined using data from both detector systems. The shower energy is determined from the integrated surface detector signals and the distance of each detector from the shower axis. The energy estimate is facilitated by the characterisation of an average lateral distributionfunction as a function of the shower energy and zenith angle. The method requires only the signal from one surface detector. Thus, it is useful for estimating the energy of hybrid events for which the geometry cannot be estimated with the surface detectors alone and the longitudinal profile measured by the fluorescence telescopes is not well determined. In the energy range 0.4 < E < 1 EeV, the methoddoubles the number of hybrid events that can be given an energy estimate. The statistical uncertainty of this energy estimate is dependent on the shower energy and geometry. For events with energy greaterthan 0.4 EeV, the median statistical uncertainty is 26% and the 90% quantile is 44%.