Cosmoglobe DR1 results. III. First full-sky model of polarized synchrotron emission from all WMAP and LFI data

We present the first model of full-sky polarized synchrotron emission that is derived from all WMAP and LFI frequency maps. The basis of this analysis is the set of end-to-end reprocessed Data Release 1 (DR1) sky maps presented in a companion paper, which have significantly lower instrumental systematics than the legacy products from each experiment. We find that the resulting polarized synchrotron amplitude map has an average noise rms per $2^ full width at half maximum (FWHM) beam of $3.2\ K $ at 30\,GHz. This is 30\, lower than the recently released model that included only LFI+WMAP data, and 29\, lower than the WMAP map alone. The mean $B$-to-$E$ power spectrum ratio is $0.39 with amplitudes consistent with those measured previously by and QUIJOTE. Assuming a power law model for the synchrotron spectral energy distribution and using the $T$--$T$ plot method, we find a full-sky inverse noise-variance-weighted mean of the synchrotron polarized spectral index of $ s from the DR1 band and 30\,GHz, in good agreement with previous estimates. In summary, the novel DR1 synchrotron model is both more sensitive and systematically cleaner than similar previous models, and it has a more complete error description that is defined by a set of Monte Carlo posterior samples. We believe that these products are preferable over previous and WMAP products for all synchrotron-related scientific applications, including simulations, forecasting, and component separation.