Maps of the ratio H calculated from selected adjacent narrow energy bands. In each panel, we indicate a larger relative strength of the harder (softer) band in blue (red), with the respective energy ranges indicated in the upper left (right) corner. The median 1σ uncertainties of H, which illustrate the typical statistical noise level in each panel, are (from left to right) 0.029, 0.032, and 0.023 in the top row, and 0.015, 0.040, and 0.13 in the bottom row. The green contours trace the broad-band surface brightness of Puppis A, as displayed in Fig. 1.