Reconstructed synchrotron photon index map. (a) Inside the red contours, the amplitude of the thermal component was over 10³ per pixel. In this area, there was on average over twice as much of the thermal component (the ratio of the mean thermal amplitude over the mean synchrotron amplitude was 2.2). (b) Same photon index map as (a) but a minimum value of the index was fixed at one. We observed that though our algorithm has found some negative values for the photon index in some pixels, they are only in areas where the thermal component drowns out the synchrotron component completely and can thus be disregarded.