a) WISE two-color composite – red: 22 μm, green: 12 μm. The red line marks the extend and position of this echoing region as previously reported in scattered light by Rest et al. (2008). This region is referenced with “O” in Table 1. b) Most distant infrared echo from Cas A at a distance  ~800 pc. The red line marks the location of the previously observed scattered light echo as reported in Rest et al. (2008), while the cyan arrow marks the direction towards Cas A. This region is referenced with “T” in Table 1. c) Color-brightness diagram of echo regions (red data points) and selected cirrus regions (black data points). The [22]–[12] color is defined as log ₁₀(F₂₂/F₁₂). Errors mainly arise from uncertainties in background subtraction and flux calibration. All infrared echoes are characterized with flux ratios  >1.0 (corresponding to a color of 0.0).