2018MNRAS.480.1393C

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 γ-ray lines and that of the electron-positron annihilation line at 511keV. The shapes of γ-ray lines associated with the decay of ⁵⁶Co (e.g. lines at 847 and 1238keV) directly reflect the velocity distribution of ⁵⁶Co. On the other hand, the 511 keV line arises from the annihilation of positions, which are also produced by the ⁵⁶Co 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.