Airborne, Far-Field Calibrators for Cosmic Microwave Background Telescopes: POLOCALC

The POLarization Orientation CALibrator for Cosmology, POLOCALC [1], is a novel method to measure the absolute orientation of the polarization plane of the Cosmic Microwave Background (CMB) photons with arcsecond accuracy. POLOCALC will dramatically improve instrumental accuracy of CMB polarimeters by means of an artificial calibration source flying on high-altitude balloons and aerial drones. The source will make use of microwave emitters between 40 and 150 GHz coupled to precise polarizing filters. The orientation of the source polarization plane will be registered to absolute celestial coordinates by star cameras and gyroscopes with arcsecond accuracy. Existing and planned CMB polarization instruments looking for primordial B-mode signals need an independent, experimental method for systematics control on the absolute polarization orientation. The lack of such a method limits the accuracy of the detection of inflationary gravitational waves, the constraining power on the neutrino sector through measurements of gravitational lensing of the CMB, the possibility of detecting Cosmic Birefringence, and the ability to measure primordial magnetic fields. Sky signals used for calibration and direct measurements of the detector orientation cannot provide an accuracy better than 1°. POLOCALC will overcome the current limitations, enabling unprecedented measurements for cosmology and fundamental physics.