Measurement of the Crab nebula polarization at 90 GHz as a calibrator for CMB experiments

Understand

CMB experiments aiming at a precise measurement of the CMB polarization, such as the Planck satellite, need a strong polarized absolute calibrator on the sky to accurately set the detectors polarization angle and the cross-polarization leakage.

• As the most intense polarized source in the microwave sky at angular scales of few arcminutes, the Crab nebula will be used for this purpose.
• Our goal was to measure the Crab nebula polarization characteristics at 90 GHz with unprecedented precision.
• The observations were carried out with the IRAM 30m telescope employing the correlation polarimeter XPOL and using two orthogonally polarized receivers.