Cosmic radio dipole from NVSS and WENSS
  We use linear estimators to determine the magnitude and direction of the
cosmic radio dipole from the NRAO VLA Sky Survey (NVSS) and the Westerbork
Northern Sky Survey (WENSS). We show that special attention has to be given to
the issues of bias due to shot noise, incomplete sky coverage and masking of
the Milky Way. We compare several different estimators and show that
conflicting claims in the literature can be attributed to the use of different
estimators. We find that the NVSS and WENSS estimates of the cosmic radio
dipole are consistent with each other and with the direction of the cosmic
microwave background (CMB) dipole. We find from the NVSS a dipole amplitude of
$(1.6 \pm 0.6) \times 10^{-2}$ in direction $(\mathrm{RA}, \mathrm{dec})=
(154^\circ \pm 21^\circ, -2^\circ \pm 21^\circ)$. This amplitude exceeds the
one expected from the CMB by a factor of about 3 and is inconsistent with the
assumption of a pure kinetic origin of the radio dipole at 99.5% CL.
