An Overview and Perspectives of the CANGAROO Observations

Akiko Kawachi

Institute for Cosmic Ray Research, Univ. of Tokyo

With the 3.8~m imaging \v Cerenkov telescope located in the southern hemisphere, Woomera (136\$^\circ\$E and 31\$^\circ\$S), the CANGAROO collaboration has observed five pulsars/nebulae in the southern sky since 1992. Unpulsed TeV gamma-ray emissions from three EGRET pulsars/nebulae (Crab, Vela, and PSR~1706-44) were detected, and possible positive detection from PSR~1509-58 was reported. The detected gamma rays are most likely produced by the inverse Compton process by electrons accelerated by terminated shock of the pulsar wind in the nebula, which also radiate synchrotron X-rays. Thus the relative intensity of inverse Compton TeV gamma rays to synchrotron X-ray emission can provide information of spatial structure of extended emission, magnetic field strength, and kinds of seed photons. The overall discussion of the CANGAROO results with another wavelength observations may provide clues to a comprehensive understanding of the mechanisms of high energy phenomena in nebulae.
A new telescope of a 7~m (to be extended as 10~m in later stage) diameter is scheduled to commence operations next year in Woomera, in order to extend CANGAROO observations down to 100~GeV energies. Significance to exploit this untouched energy region between the limits of the satellites and of the \v Cerenkov telescopes so far, will also be discussed.