Images of the detected number of counts per pixel in eight energy bands (from 4 to 12 keV) integrated over all 1.74 × 10⁵ s of TVAC data where no X-ray source is present (background exposures only). The heat-pipe noise appears in the 4–8 keV energy band as pixels with abnormally high count rates. (One detector module of 4 × 8 pixels on the right does not work nominally. It shows zero counts).