Upper Limits on the Pulsed VHE gamma-ray Emission from Two Young Pulsars Investigated with the High Energy Stereoscopic System

Abstract

The High Energy Stereoscopic System (H.E.S.S.) is a system of four, imaging, atmospheric Cherenkov telescopes in Namibia, designed to detect very-high-energy gamma rays above ~ 100 GeV. During 2002--2003, H.E.S.S. collected data from two, young and energetic radio pulsars: the Crab and PSR B1706-44. We searched for pulsations at the lowest energies that H.E.S.S. is capable of detecting, aiming at a detection that would potentially differentiate between the two popular models of pulsar high-energy emission: the Polar Cap and the Outer Gap. No evidence for pulsed emission was found in the data, and upperlimits were derived to a 99.95% confidence level. Our assumptions and upper limit values for the two pulsars are reported.