A response to Rubin & Heitlauf: "Is the expansion of the universe
  accelerating? All signs still point to yes"
  We have shown (Colin et al., 2019) that the acceleration of the Hubble
expansion rate inferred from Type Ia supernovae (SNe Ia) is, at $3.9\sigma$
significance, a dipole approximately aligned with the CMB dipole, while its
monopole component, which can be interpreted as due to a Cosmological Constant
or dark energy, is consistent with zero at $1.4\sigma$. This has been
challenged by Rubin & Heitlauf (2019) who assert that the dipole arises because
we made an incorrect assumption about the SNe Ia light-curve parameters (viz.
took them to be sample- and redshift independent), and did not allow for the
motion of the Solar system (w.r.t. the 'CMB frame' in which the CMB dipole
supposedly vanishes). In fact what has an even larger impact on our finding is
that we reversed the inconsistent "corrections" made for the peculiar
velocities of the SNe Ia host galaxies w.r.t the CMB frame, which in fact serve
to bias the lever arm of the Hubble diagram towards higher inferred values of
the monopole. We demonstrate that even if all such corrections are made
consistently and both sample- and redshift-dependence is allowed for in the
standardisation of supernova light curves, the evidence for isotropic
acceleration rises to just $2.8\,\sigma$. Thus the criticism of Rubin &
Heitlauf serves only to highlight that "corrections" must be made to the SNe Ia
data assuming the standard $\Lambda$CDM model, in order to recover it from the
data.
