The Crab Nebula as a Calibrator for wide-beam Cosmic Microwave Background polarization surveys

We analyze the effect of polarized diffuse emission in the calibration of wide-beam mm-wave polarimeters, when using the Crab Nebula as a reference source for both polarized brightness and polarization angle. We show that, for CMB polarization experiments aiming at detecting B-mode in a scenario with a tensor to scalar ratio \(r \sim 0.001\), wide (a few degrees in diameter), precise (\(\sigma_Q\) , \(\sigma_U\) \(\sim\) 20 $\mu$$K_{CMB}\( arcmin), high angular resolution (\)< \mathrm{FWHM}$) reference maps are needed to properly take into account the effects of diffuse polarized emission and avoid significant bias in the calibration.