High Energy Gamma-Ray Observations of Peculiar Objects such as Pulsars and Active Galaxies

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(1) We have, by the end of the fiscal year 1994, obtained evidence of VHE (very high energy) gamma rays from Crab nebula and PSR B 1706-44. The data obtained in 1993 and 1994 suggested an interesting hint of VHE gamma ray signal from Vela pulsar direction, and data analysis, adding 1995 observation, was continued on the Vela as well as on other various objects in the southern sky.(2) We found that evidence of VHE gamma rays from Vela pulsar direction exist in all of the Vela data set over 1993 to 1995. The observed signal appears as "unpulsed" (not modulated with the pulsar period of 89 msec) and the emission region of VHE gamma rays is extended with its maximum intensity shifted by about 0.1ﾟ from the pulsar position. These features suggest that the VHE emission is not from the pulsar magnetosphere. A "wind" of energetic electrons and positrons (pulsar wind) is believed to be ejected from pulsar, causing a shock by colliding with circumstellar matter to emit gamma rays. It is likely that we have seen such a phenomenon in vicinity of the Vela pulsar.(3) From a binary pulsar PSR B 1259-63, we obtained evidence of about 5sigma significance, which encourages repeated observation.(4) We set an upper limit of VHE gamma ray flux from PKS 0521-365, the second nearest AGN (active galactic nuclei) among the GeV gamma ray AGN detected by the gamma ray satellite of Compton Gamma Ray Observatory. The result constrains on various models of gamma ray production as well as on infrared intensity in the extragalactic space.(5) We also studied an intesting object of GeV gamma ray source, CGRO J 1758-23, which includes supernova remnant, pulsar, radio point source and molecular cloud etc. No evidence of VHE gamma rays that appears as a point source was so far discovered, and the case of extended emission remains to be more carefully examined.(6) Prelimiary analysis shows no evidence of VHE emission from other objects such as AGN Centaurus A and pulsar PSR B 1055-52.