Top left: spectral index image between 325 and 1400 MHz. The image has a FWHM of 53′′  ×  53′′. The iso-contours represent the 1400 MHz image convolved to a resolution of 53′′  ×  53′′ and corrected for the primary beam attenuation. The first contour level is drawn at 0.45 mJy beam^-1 and the rest are spaced by a factor of 2. The sensitivity (1-σ) is 0.15 mJy beam^-1. The image at 325 MHz, convolved and primary beam corrected, has a sensitivity (1-σ) of 2.5 mJy beam^-1. Top right: image of the spectral index uncertainty. Bottom: spectrum between 325 MHz and 1400 MHz in the four sample positions indicated in the top right panel.