Improving Planck calibration by including frequency-dependent relativistic corrections

TL;DR

This paper highlights the importance of including frequency-dependent relativistic corrections in Planck satellite calibration, which could significantly improve the accuracy of future data by addressing current systematic errors.

Contribution

It introduces the frequency-dependent relativistic correction factor for Planck calibration, emphasizing its significance at high frequencies and potential to reduce systematic errors.

Findings

Relativistic corrections vary with frequency, especially at high frequencies.

Current calibration errors are dominated by systematics, affecting polarization data.

Including these corrections could improve future Planck data accuracy.

Abstract

The Planck satellite detectors are calibrated in the 2015 release using the "orbital dipole", which is the time-dependent dipole generated by the Doppler effect due to the motion of the satellite around the Sun. Such an effect has also relativistic time-dependent corrections of relative magnitude 10^(-3), due to coupling with the "solar dipole" (the motion of the Sun compared to the CMB rest frame), which are included in the data calibration by the Planck collaboration. We point out that such corrections are subject to a frequency-dependent multiplicative factor. This factor differs from unity especially at the highest frequencies, relevant for the HFI instrument. Since currently Planck calibration errors are dominated by systematics, to the point that polarization data is currently unreliable at large scales, such a correction can in principle be highly relevant for future data releases.