Diagnosing Timing Error in WMAP Data

TL;DR

This paper identifies a significant uncorrected timing error in WMAP data processing that affects the accuracy of the CMB quadrupole measurement, highlighting the importance of precise timing in cosmological data analysis.

Contribution

It provides direct evidence of a timing offset in WMAP data and demonstrates its impact on the estimated CMB quadrupole, improving understanding of potential systematic errors.

Findings

Detected a significant timing offset in WMAP TOD data.

Showed that the uncorrected timing error inflates the CMB quadrupole estimate.

Confirmed previous indirect evidence of timing-related errors.

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 -25.6ms between the timestamps of the spacecraft attitude and radiometer output in the original raw WMAP time-ordered data (TOD), which, if not corrected in following 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 -25.6ms 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, 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.