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Fig. 5

image

Multiepoch VLT spectropolarimetric observations of SN 2012aw showing the total flux FI at the top, the observed polarization angle θP (we show thequantity 180 + , in degrees), and the observed percentage polarization P (we show here the traditional polarization defined as ; see, e.g., Leonard et al. 2001). The quantities θP and P are displayed with a binning of 15 Å/bin. Each epoch is color coded (see labels and Table 2). To help gauge the reality of spectropolarimetric features, in the bottom plot we show a representative uncertainty per 15Å bin for each epoch (color coded error bars in the upper left corner), taken as the mean 1σ uncertainty in the total polarization calculated from 6900 Å to 7400 Å, a region largely free of line features at all epochs. (The particular uncertainty in any given bin rises and falls with the S/N, becoming larger in the P Cygni troughs and smaller in the peaks.) We overplot the adopted interstellar polarization based on a Serkowski law (Serkowski et al. 1975; Cikota et al. 2017) derived by assuming that the intrinsic polarization is zero at the regions of the strong, consistent, depolarization seen near the flux emission peaks of Hβ, Na i D, Hα, and the Ca ii near-infrared triplet at epoch 6 (thick black line; see Sect. 4.2 for details).

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