  Recent studies have indicated that an anisotropic cosmic expansion may exist.
In this paper, we use three datasets of type Ia supernovae (SNe Ia) to probe
the isotropy of cosmic acceleration. For the Union2.1 dataset, the direction
and magnitude of the dipole are $(l=309.3^{\circ} {}^{+
15.5^{\circ}}_{-15.7^{\circ}} ,\ b = -8.9^{\circ} {}^{ +
11.2^{\circ}}_{-9.8^{\circ}} ),\ A=(1.46 \pm 0.56) \times 10^{-3}$. For the
Constitution dataset, the results are $(l=67.0^{\circ}{}^{+
66.5^{\circ}}_{-66.2^{\circ}},\ b=-0.6^{\circ}{}^{+
25.2^{\circ}}_{-26.3^{\circ}}),\ A=(4.4 \pm 5.0) \times 10^{-4}$. For the JLA
dataset, no significant dipolar deviation is found. We also explore the effects
of anisotropic distributions of coordinates and redshifts on the results using
Monte-Carlo simulations. We find that the anisotropic distribution of
coordinates can cause dipole directions and make dipole magnitude larger.
Anisotropic distribution of redshifts is found to have no significant effect on
dipole fitting results.
