Effects of thermal fluctuations in the SPOrt experiment

¹ IASF/CNR Bologna, via Gobetti 101, 40129 Bologna, Italy e-mail: carretti@bo.iasf.cnr.it
² IASF/CNR Milano, via Bassini 15, 20133 Milano, Italy

Received: 29 April 2004
Accepted: 20 August 2004

Abstract

The role of systematic errors induced by thermal fluctuations is analyzed for the SPOrt experiment with the aim at estimating their impact on the measurement of the Cosmic Microwave Background Polarization (CMBP). The transfer functions of the antenna devices from temperature to data fluctuations are computed, by writing them in terms of both instrument and thermal environment parameters. In addition, the corresponding contamination maps are estimated, along with their polarized power spectra, for different behaviours of the instabilities. The result is that thermal effects are at a negligible level even for fluctuations correlated with the Sun illumination provided their frequency f_tf is larger than that of the Sun illumination (f_day) by a factor , which defines a requirement for the statistical properties of the temperature behaviour. The analysis with actual SPOrt operative parameters shows that the instrument is only weakly sensitive to temperature instabilities, the main contribution coming from the cryogenic stage. The contamination on the E-mode spectrum does not significantly pollute the CMBP signal and no specific data cleaning seems to be needed.