Inference of the cosmic rest-frame from supernovae Ia
  We determine the proper motion of the Solar system from the Pantheon sample
of supernovae (SNe) of type Ia. The posterior distribution of the Solar system
proper velocity, its direction and relevant cosmological parameters are
obtained based on the observed distance moduli, heliocentric redshifts, and
positions of SNe by means of a Markov Chain Monte Carlo method. We account for
the unknown peculiar motion of SNe by including their expected covariance from
linear theory. We find that the Solar system moves with $v_o = 249 \pm 51$ km/s
towards $RA = 166 \pm 16$ deg, $Dec = 10 \pm 19$ deg (J2000) (all at 68\%
C.L.). The direction of motion agrees with the direction of the dipole observed
in the cosmic microwave background (CMB) ($RA = 166$ deg, $Dec = -7$ deg). The
inferred velocity is $2.4 \sigma$ smaller than the value inferred from a purely
kinematic interpretation of the CMB dipole ($370$ km/s). Assuming a flat
$\Lambda$ cold dark matter model, we find no degeneracy of Solar proper motion
with other cosmological parameters. The dimensionless matter density is
$\Omega_M = 0.305 \pm 0.022$, in excellent agreement with CMB measurements. We
also find no degeneracy of the Solar proper motion with the SN calibration
nuisance parameter. We conclude that a larger sample of SNe will allow an
independent and robust test of the kinematic nature of the CMB dipole.
