Measurement of sky clarity using MIR radiometers as an adjunct to atmospheric Čerenkov radiation measurements

A technique for detecting the presence of cloud in the field of view of an atmospheric Cerenkov telescope using a far infra red radiometer is described. Models for the radiative emission from clear and cloudy skies are tested and found to represent the measurements.Comment: 13 pages, 10 figures, submitted to Experimental Astronom

A Search for Very High Energy Gamma Rays from Active Galactic Nuclei Visible from the Southern Hemisphere

Observations have been made, using the University of Durham Mark 6 gamma ray telescope, of the very high energy gamma ray emission from a number of active galactic nuclei visible from the Southern hemisphere. Limits are presented to the VHE gamma ray emission from 1ES 0323+022, PKS 0829+046, 1ES 1101--232, Cen A, PKS 1514-24, RXJ 10578-275, and 1ES 2316-423, both for steady long-term emission and for outbursts of emission on timescales of 1 day.Comment: 13 pages, 1 figure, accepted for publication in Ap.