Systematic distortion in cosmic microwave background maps

To minimize instrumentally the induced systematic errors, cosmic microwave background (CMB) anisotropy experiments measure temperature differences across the sky using pairs of horn antennas, temperature map is recovered from temperature difference obtained in sky survey through a map-making procedure. To inspect and calibrate residual systematic errors in the recovered temperature maps is important as most previous studies of cosmology are based on these maps. By analyzing pixel-ring coupling and latitude dependence of CMB temperatures, we find notable systematic deviation from CMB Gaussianity in released Wilkinson Microwave Anisotropy Probe (WMAP) maps. The detected deviation cannot be explained by the best-fit LCDM cosmological model at a confidence level above 99% and cannot be ignored for a precision cosmology study.