Diagnosing timing error in WMAP data

ABSTRACT The Doppler dipole signal dominates the cosmic microwave background (CMB) anisotropy maps obtained by the Wilkinson Microwave Anisotropy Probe (WMAP) mission, and plays a key role throughout the data processing. Previously, we discovered a timing asynchronism of −25.6 ms between the timestamps of the spacecraft attitude and radiometer output in the original raw WMAP time‐ordered data (TOD), which, if not corrected during data processing, would generate an artificial quadrupole component (l= 2) in recovered CMB maps (Liu, Xiong & Li 2010). Recently, Roukema (2010b) proves that there does exist a timing offset‐induced error corresponding to about −25.6 ms in the WMAP calibrated TOD, by studying the fluctuation variance per pixel in the temperature map recovered from the TOD as a function of assumed timing offset. Here, we find evidence directly in the WMAP TOD for such an uncorrected timing error, which possibly occurred in calculating the Doppler dipole signal during the WMAP team's TOD data processing. The amplitude is highly significant and is consistent with previous work. We also show that the uncorrected timing offset can lead the WMAP CMB quadrupole to be substantially overestimated.