Calibration of the particle background b parameter as a function of the local background fit by XAmin 3.5 in various equal-area off-axis bins for MOS (left) and PN (right panel) based on the point-source simulations. Off-axis bin boundaries are represented with vertical dashed lines and data points are slightly shifted on the x-axis for readability. Here, b = 1 is the so-called nominal particle background, i.e. close to the most common level encountered in X-CLASS observations. In simulations, particle background is injected at a level of b times the nominal value. The pixel size is 2.5″ × 2.5″.