  We discuss gamma-ray signatures associated with an asymmetric explosion and
transport of positrons in SN Ia ejecta. In particular, Compton scattering of
gamma-ray line photons can induce polarization in the continuum, which would be
a direct probe of the asymmetries in the distribution of radioactive isotopes
and/or of the scattering medium. Even more interesting would be a comparison of
the shapes of $\gamma$-ray lines and that of the electron-positron annihilation
line at 511 keV. The shapes of $\gamma$-ray lines associated with the decay of
Co56 (e.g., lines at 847 and 1238 keV) directly reflect the velocity
distribution of Co56. On the other hand, the 511 keV line arises from the
annihilation of positions, which are also produced by the Co56 decay but can
propagate through the ejecta before they slow down and annihilate. Therefore,
the shape of the annihilation line might differ from other gamma-ray lines,
providing constraints on the efficiency of positrons propagation through the
ejecta and, as consequence, on the topology of magnetic fields in the ejecta
and on the fraction of positrons that escape to the interstellar medium. We
illustrate the above effects with two models aimed at capturing the main
predicted signatures.
