Distribution of the sample based on the factor (F=F_bright/F_faint) and significance $\left(S=\frac{F_{\mathrm{bright}}-F_{\mathrm{faint}}}{\sqrt{F_{\mathrm{bright},\mathrm{err}}^2+F_{\mathrm{faint},\mathrm{err}}^2}}\right)$ values (see Sect. 2.2). For each source, the factor and significance are calculated between the bright and faint states represented by the blue-shaded area in Fig. 1. We make a cut at F>5 and highlight the 16 sources that will be the focus of this paper. The remaining extragalactic sources of the sample are displayed with triangles.