High-Energy Gamma-Ray Observations of W Comae with STACEE

We report on observations of the blazar W Comae (ON+231) with the Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE), a wavefront-sampling atmospheric Cherenkov telescope, in the spring of 2003. In a data set comprising 10.5 hours of ON-source observing time, we detect no significant emission from W Comae. We discuss the implications of our results in the context of the composition of the relativistic jet in W Comae, examining both leptonic and hadronic models for the jet. We derive 95% confidence level upper limits on the flux at the level of 1.5–3.5 × 10 - 10 cm - 2 s - 1 above 100 GeV for the leptonic models, or 0.5–1.1 × 10 - 10 cm - 2 s - 1 above 150 GeV for the hadronic models.