CANGAROO-III OBSERVATIONS OF THE 2006 OUTBURST OF PKS 2155-304

摘要

We have used the CANGAROO-III imaging atmospheric Cerenkov telescopes to observe the high-frequency-peaked BL Lacertae (HBL) object PKS 2155-304 between 2006 July 28 (MJD 53,944) and August 2, triggered by the H.E.S.S. report that the source was in a high state of TeV gamma-ray emission. A signal was detected at the 4.8 σ level in an effective live time of 25.1 hr during the outburst period. The flux of very high energy gamma rays from the CANGAROO-III observations shows variability on the timescale of less than a few hours. The averaged integral flux above 660 GeVis (1.6 ± 0.3_(stat) ± 0.5_(syst)) × 10~(11) cm~(-2) s~(-1), which corresponds to ～45% of the flux observed from the Crab Nebula. Follow-up observations between August 17 (MJD 53,964) and 25 indicate that the source activity had decreased.