tokens: for a standing shock just downstream of the radio core that compresses and aligns the magnetic field (Cawthorne Cobb 1990 ). Figure 5. Variations of the emission parameters of 3C 273 transverse to the jet axis (dashed red line) for slice 6 (shown in Figure 3 ). From top to bottom: total intensity, polarized intensity, fractional polarization, and EVPA. The fractional polarization increasing toward the edges of the jet is a predicted polarimetric signature of a jet sheath (as discussed in Section 1 ), with the EVPA transverse to the axis. The black line in the lower panel delineates EVPAs that are exactly ⊥ to the jet spine. The beam width along this transverse slice is shown in the upper panel to the left. 4.2. 4C 71.07 Figure 6 presents a stacked radio map of the blazar 4C 71.07 (0836+710). A very prominent and continuous polarimetric signature of a jet sheath is evident down the edges of the jet in this stacked radio image. Given the continuous nature of the jet sheath on the image, we can estimate the bolometric luminosity of the sheath. This is accomplished by first using the length of the polarized intensity profile along each of the slices to trace out the shaded gray regions shown in Figure 9 (see also Figure 6 ). The size of the sheath on each side of the slice is arbitrarily set by the location where the polarized flux falls below 0.85 times the peak value. An estimate of the bolometric luminosity () of the sheath is determined by summing up all of the deconvolved “sheath” flux (see Figures 8 and 9 ) contained within the gray shaded regions of our stacked map. We convert this extrapolated sheath flux at 43 GHz into a spectral luminosity and assume a power law (), which we then integrate over a range of frequencies that encompass the sheath’s radiation to obtain where we have adopted a spectral index of and limits of integration of and . Our estimate indicates that the jet sheath can potentially provide a substantial source of seed photons even at parsec scales along the jet. It should be pointed out, however, that the beam width is ∼0.2 mas along our transverse slices and that the sheath region we detect is within ∼0.05–0.15 mas of the jet spine. Convolution with the beam, therefore, adds a significant contribution of flux from the spine to our nominal sheath region. As illustrated in Figures 8 and 9 (solid red lines) we attempt to remove this contaminating spine flux from our estimate. The bolometric luminosity given in Equation ( 1 ), however, should only be regarded as a rough estimate of the actual sheath luminosity. Figure 6. Stacked map of 43 GHz images of 4C 71.07 spanning 20 epochs of observation from 2008 to 2016. As in Figure 3 , the black contours correspond to total intensity (contour levels are: 0.9, 1.9, 3.9, 7.9, 15.8, 31.7, 63.4, 126.9, 253.9, 507.8 mJy beam −1 ), whereas the underlying color scheme corresponds to polarized intensity (see the color bar to the right for the flux levels), with the EVPAs denoted by the
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