Anisotropy of the Universe via the Pantheon supernovae sample revisited
  We employ the hemisphere comparison (HC) method and the dipole fitting (DF)
method to investigate the cosmic anisotropy in the recently released Pantheon
sample of type Ia supernovae (SNe Ia) and five combinations among Pantheon. For
the HC method, we find the maximum anisotropy level in the full Pantheon sample
is $\mathrm{AL}_{max}=0.361\pm0.070$ and corresponding direction
$(l,b)=({123.05^{\circ}}^{+11.25^{\circ}}_{-4.22^{\circ}},
{4.78^{\circ}}^{+1.80^{\circ}}_{-8.36^{\circ}})$. A robust check shows the
statistical significance of maximum anisotropy level is about $2.1\sigma$. We
also find that the Low-$z$ and SNLS subsamples have decisive impact on the
overall anisotropy while other three subsamples have little impact. Moreover,
the anisotropy level map significantly rely on the inhomogeneous distribution
of SNe Ia in the sky. For the DF method, we find the dipole anisotropy in the
Pantheon sample is very weak. The dipole magnitude is constrained to be less
than $1.16\times10^{-3}$ at $95\%$ confidence level. However, the dipole
direction is well inferred by MCMC method and it points towards
$(l,b)=({306.00^{\circ}}^{+82.95^{\circ}}_{-125.01^{\circ}},
{-34.20^{\circ}}^{+16.82^{\circ}}_{-54.93^{\circ}})$. This direction is very
close to the axial direction to the plane of SDSS subsample. It may imply that
SDSS subsample is the decisive part to the dipole anisotropy in the full
Pantheon sample. All these facts imply that the cosmic anisotropy found in
Pantheon sample significantly rely on the inhomogeneous distribution of SNe Ia
in the sky. More homogeneous distribution of SNe Ia is necessary to search for
a more convincing cosmic anisotropy.
