  Observations of cosmic microwave background polarisation, essential for
probing a potential phase of inflation in the early universe, suffer from
contamination by polarised emission from the Galactic interstellar medium. This
work combines existing observations from the WMAP and Planck space missions to
make a low-noise map of polarised synchrotron emission that can be used to
clean forthcoming CMB observations. We combine WMAP K, Ka and Q maps with
Planck LFI 30~GHz and 44~GHz maps using weights that near-optimally combine the
observations as a function of sky direction, angular scale, and polarisation
orientation. We publish well-characterised maps of synchrotron Q and U Stokes
parameters at nu = 30GHz and 1 degree angular resolution. A statistical
description of uncertainties is provided with Monte-Carlo simulations of
additive and multiplicative errors. Our maps are the most sensitive full-sky
maps of synchrotron polarisation to date, and are made available to the
scientific community on a dedicated web site.
