Edwin Budding

Possible observation of 100 TeV gamma rays from the active galaxy Centaurus a

Abstract We have searched for evidence of ultra-high energy gamma rays from the active galaxy Centaurus A in the data set of the JANZOS experiment during the period 13 October 1987 to 18 January 1992. No significant DC excess was found from this source. Excess events were found, however, in the period 14 April – 3 June 1990. The duration of the excess, 48 days, and equivalent luminosity, ~ 10 43 erg s −1 , are both similar to those measured previously for X-ray outbursts of Centaurus A. Furthermore, the events appear to exhibit the expected absorption feature at 200 TeV due to interactions with the 2.7 K background radiation, but the chance probability for the excess is at the 2% level. The equivalent time averaged flux during this period was (5.5 ± 1.5) × 10 −12 photons cm −2 s −1 at energies ≥ 110 TeV, about 20 times as large as the upper lim of steady emission, assuming a differential spectral index of −2.0. Further observations are required to confirm the result

Upper limits on TeV gamma-ray emission from centaurus A, vela X-1, centaurus X-3, and circinus X-1

The active galaxy Centaurus A and the X-ray binary systems Vela X-1, Centaurus X-3, and Circinus X-1 were monitored for VHE gamma-ray emission above 1 TeV with the JANZOS Cerenkov facility during 1988 and 1989. No evidence was found for persistent or episodic emission from any of these objects. Subsequent upper limits on the integral fluxes of 2.2×10 −11 , 2.8×10 −11 , 4.0×10 −11 ,and 4.2×10 −11 cm −1 s −1 , respectively, were obtained for these objects. These limits are consistent with results of observations made by other groups

Survey of ultra-high-energy gamma-ray emission in the Magellanic Clouds

Various objects in the Magellanic Clouds were monitored for ultra-high-energy (UHE) gamma-ray emission during 1988 and 1990 using Cerenkov technique at large zenith angles with the JANZOS facility. During 1990 the equipment was modified to allow a sky coverage of 7°×23° at large zenith angles. This enabled most of the extent of the Large Magellanic Cloud to be surveyed at ultra-high energies. An examination of the data base yielded no clear evidence for persistent UHE emission from SN 1987A and selected X-ray pulsars in the Magellanic Clouds