EDP Sciences
Free access
Volume 409, Number 1, October I 2003
Page(s) 375 - 385
Section Physical and chemical processes
DOI http://dx.doi.org/10.1051/0004-6361:20030927

A&A 409, 375-385 (2003)
DOI: 10.1051/0004-6361:20030927

Optimized in-flight absolute calibration for extended CMB surveys

B. Cappellini1, D. Maino1, 2, G. Albetti2, P. Platania1, R. Paladini3, A. Mennella4 and M. Bersanelli1, 4

1  Università degli Studi di Milano, via Celoria 16, 20133 Milano, Italy
2  INAF-Osservatorio Astronomico, via G. B. Tiepolo 11, 34131 Trieste, Italy
3  SISSA/ISAS, Astrophysics Sector, via Beirut 4, 34014 Trieste, Italy
4  IASF, CNR, via Bassini 15, 20133 Milano, Italy

(Received 8 October 2002 / Accepted 4 June 2003 )

Accurate measurements of the Cosmic Microwave Background (CMB) anisotropy call for high precision and reliability of the in-flight calibration. For extended surveys the CMB dipole provides an excellent calibration source at frequencies lower than ~200 GHz; however poorly known foreground emissions, such as diffuse galactic components, complicate the signal and introduce a systematic error in the calibration. We show that introducing a weight function that takes into account the uncertainty in the a priori knowledge of the sky, allows us to substantially improve the calibration accuracy with respect to methods involving galactic latitude cuts. This new method is tested for PLANCK-LFI radiometers at 30 and 100 GHz. On short time scales (less than 1 day) the absolute calibration of each channel can be recovered with an overall 1-2% accuracy. We also consider the effect of CMB anisotropy itself on the calibration, and find that knowledge of the CMB pattern on large scales is needed to keep the short-time scale calibration accuracy within 1%.

Key words: cosmology: cosmic microwave background -- methods: data analysis

Offprint request: B. Cappellini, Benedetta.Cappellini@mi.infn.it

© ESO 2003