Our sensitivity limits (left, at 150 MHz) compared to applicable earlier work. For previous searches that did not cover the entire supernova remnant size, the searched fraction is indicated. Per frequency only the most sensitive limits obtained are shown. A grid is overlaid with spectral slope α = −1.4 to indicate the scaling of our sensitivity limits (Bates et al. 2013). For visibility our limits are plotted slightly offset from the 150 MHz observing frequency (dashed line).