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Polarized microwave source in space
We propose to build an artificial polarized microwave source and install it in space to be in the far-field of large ground-based telescopes in Europe and Chile. The easiest step into space would be to launch the source on a nano-satellite into a low-earth orbit. Unfortunately, on such an orbit the source would move too quickly in the sky (a degree per second) to be tracked by large microwave telescopes such as the IRAM 30m and the Sardinia radio telescope.
Our plan is to install the COSMOCal source as a guest payload on a geostationary orbit (GEO) satellite to be launched by Eutelsat group in 2030. The source will be visible at a fixed position in the sky. It can be observed from the ground during long integration periods at a constant altitude, i.e., with a fixed background and minimal fluctuations in atmospheric emissions.
Ground-based observatories
COSMOCal will be used to calibrate polarization observations from a complementary set of ground-based pilot observatories that comprises the IRAM 30 m and the Sardinia radio 64 m telescope (SRT) in Europe, and the large telescope of the Simons Observatory (SO) in Chile (SO Collaboration 2019). The use of the IRAM 30 m telescope and SRT is supported by the expertise of the COSMOCal collaboration with these facilities, that of SO by an established collaboration involving team members at APC and Milano Bicocca.
The IRAM 30 m and SRT are equipped with instruments dedicated to galactic and extragalactic astrophysics. The SO is the primary experiment in Chile focused on measuring CMB anisotropies. Two additional telescopes, the large millimetre telescope (LMT) in Mexico and the Fred Young Submillimeter Telescope (FYST) in Chile, could also be used in conjunction with COSMOCal, but this is not required to achieve our science goal.
Once precisely calibrated with COSMOCal, telescopes at the pilot observatories will allow us to map astrophysical sources with very high precision and then offer well determined reference for any other polarization experiment, such as the south pole telescope and the CMB space mission LiteBIRD, which cannot point at the COSMOCal source.
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