Top left: burn law a in rad²/m⁴ calculated using the images at 1443, 1465, 1515, 1630, and 6600 MHz smoothed with a FWHM Gaussian of 2.9′. The image is derived from a fit of FPOL as a function of λ⁴ following the Eq. (5). The color range is from −500 to 1300 rad²/m⁴. Contours refer to the total intensity image at 1443 MHz. The radio contours are drawn at 3σ_I and the rest are spaced by a factor of 2. Top right: histogram of the Burn law a distribution. Bottom: plots of fractional polarization FPOL as a function of λ⁴ at four different source locations.