Global spectral energy distribution of the Crab Nebula in the prospect of the Planck satellite polarisation calibration

TL;DR

This study analyzes the Crab Nebula's spectral energy distribution across a wide frequency range to support Planck satellite polarization calibration, confirming synchrotron emission dominance and setting error bounds for polarization measurements.

Contribution

It provides a comprehensive multi-frequency SED analysis of the Crab Nebula, validating its use as a polarization calibrator for the Planck satellite.

Findings

Crab Nebula's microwave emission is consistent with radio synchrotron emission.

Upper limits on millimetre excess components' impact on polarization accuracy.

Supports Planck's use of Crab Nebula for polarization calibration.

Abstract

Whithin the framework of the Planck satellite polarisation calibration, we present a study of the Crab Nebula spectral energy distribution (SED) over more than 6 decades in frequency ranging from 1 to $\rm 10^6 GHz$. The Planck satellite mission observes the sky from 30 to 857 GHz and therefore we focus on the millimetre region. We use radio and submillimetre data from the WMAP satellite between 23 and 94 GHz (from 13 to 3.18 mm) and from the Archeops balloon experiment between 143 (2.1 mm) and 545 GHz (0.55 mm), and a compendium of other Crab Nebula observations. The Crab SED is compared to models including three main components : synchrotron which is responsible for the emission at low and at high frequencies, dust which explains the excess of flux observed by the IRAS satellite and an extra component on the millimetre regime. From this analysis we conclude that the unpolarised emission of the Crab Nebula at microwave and millimetre wavelengths is the same synchrotron emission that the one observed in the radio domain. Therefore, we expect the millimetre emission of the Crab nebula to be polarised with the same degree of polarisation and orientation than the radio emission. We set upper limits on the possible errors induced by any millimetre extra component on the reconstruction of the degree and angle of polarisation at the percent level as a maximum. This result strongly supports the choice by the Planck collaboration of the Crab nebula emission for performing polarisation cross-checks in the range 30 (299 mm) to 353 GHz (0.849 mm).