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A&A Supplement series, Vol 121, February 1997, 393-404

Received March 7; accepted June 7, 1996

Sub-degree CMB anisotropy from space

II. In-flight calibration

M. Bersanellitex2html_wrap1406, P.F. Muciacciatex2html_wrap1408, P. Natolitex2html_wrap1410, N. Vittoriotex2html_wrap1412, - N. Mandolesitex2html_wrap1414

Send offprint request: M. Bersanelli

tex2html_wrap1416  Istituto di Fisica Cosmica, CNR, Milano, Italy
tex2html_wrap1418  Dipartimento di Fisica, Universita' di Tor Vergata, Roma, Italy
tex2html_wrap1420  Istituto TESRE, CNR, Bologna, Italy


In the context of the COBRAS/SAMBA mission studytex2html_wrap_inline1384, we discuss in-flight calibration of extended sky maps of the microwave sky using celestial sources. We simulate the observations in order to assess the accuracy obtainable for absolute and relative calibration of the Low Frequency Instrument (LFI), operating in the 30-130 GHz range. Accurate calibration can be achieved using the CMB dipole signal, tex2html_wrap_inline1388. With conservative assumptions on the effect of Galactic contamination, we find that the CMB dipole will provide absolute calibration accuracy tex2html_wrap_inline1390 (limited by the COBE-DMR uncertainty on tex2html_wrap_inline1392) on time-scales of about 10 days at all frequencies and for the entire mission lifetime. Long-term calibration with accuracy tex2html_wrap_inline1394 can be obtained using the spacecraft orbital velocity. Additional, independent calibration will be provided by the observation of external planets. We also describe the capability of the proposed scanning technique to detect and remove long-term instrumental drifts, and show that these effects, if present, can be controlled and removed with an overall negligible impact on the data uncertainty.

keywords: cosmic microwave background -- radio continuum: general -- space vehicles

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