radial distribution of SNe {#resdiscus_sub2}
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The upper panel of Fig. \[hist\_distr\] compares the distributions of deprojected, normalized galactocentric radii ($\tilde{r}=R_{\rm SN}/R_{25}$) of Type Ia and CC SNe in S0–S0/a and Sa–Sm galaxies. In this panel, we see an initial rise of SNe number as a function of $\tilde{r}$ and a negative radial gradient outside the maximum, suggestive of the exponential surface brightness distribution of stellar discs, which we will study in more detail in Section \[resdiscus\_sub3\]. In previous studies, based on smaller samples, similar deprojected distributions of SNe were already obtained by normalizing them to the radii of hosts at some fixed surface brightness isophot (; ; ).

The observed numbers of SNe at $\tilde{r} \lesssim 0.2$ indicate that different SN searches fail to discover objects at or near the centre of the surveyed galaxies . In an earlier study, noted that this effect is stronger for distant host galaxies relative to nearer ones. Then it became apparent that this *Shaw effect* is important for deep photographic searches and negligible for visual and CCD searches . Presently, SN searches are conducted only with CCD cameras and SNe 