Observation of Very High Energy Gamma Rays from HESS J1804-216 with CANGAROO-III Telescopes

We observed the unidentified TeV gamma-ray source HESS J1804-216 with the CANGAROO-III atmospheric Cerenkov telescopes from 2006 May to July. We detected very high energy gamma rays above 600 GeVat the 10 sigma level in an effective exposure of 76 hr. We obtained a differential flux of (5: 0 +/- 1.5(stat) +/- 1.6(sys))x 10(-12)(E/1 TeV)(-alpha) cm(-2) s(-1) TeV-1 with a photon index alpha of 2.69 +/- 0.30stat +/- 0.34(sys), which is consistent with that of the H. E. S. S. observation in 2004. We also confirm the extended morphology of the source. By combining our result with multiwavelength observations, we discuss the possible counterparts of HESS J1804-216 and the radiation mechanism based on leptonic and hadronic processes for a supernova remnant and a pulsar wind nebula.