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The violent merger of two carbon-oxygen white dwarfs has been proposed as aviable progenitor for some Type Ia supernovae. However, it has been argued thatthe strong ejecta asymmetries produced by this model might be inconsistent withthe low degree of polarisation typically observed in Type Ia supernovaexplosions. Here, we test this claim by carrying out a spectropolarimetricanalysis for the model proposed by Pakmor et al. (2012) for an explosiontriggered during the merger of a 1.1 M$_{\odot}$ and 0.9 M$_{\odot}$carbon-oxygen white dwarf binary system. Owing to the asymmetries of theejecta, the polarisation signal varies significantly with viewing angle. Wefind that polarisation levels for observers in the equatorial plane are modest($\lesssim$ 1 per cent) and show clear evidence for a dominant axis, as aconsequence of the ejecta symmetry about the orbital plane. In contrast,orientations out of the plane are associated with higher degrees ofpolarisation and departures from a dominant axis. While the particular modelstudied here gives a good match to highly-polarised events such as SN 2004dt,it has difficulties in reproducing the low polarisation levels commonlyobserved in normal Type Ia supernovae. Specifically, we find that significantasymmetries in the element distribution result in a wealth of strongpolarisation features that are not observed in the majority of currentlyavailable spectropolarimetric data of Type Ia supernovae. Future studies willmap out the parameter space of the merger scenario to investigate ifalternative models can provide better agreement with observations.

Type Ia supernovae from violent mergers of carbon-oxygen white dwarfs: polarisation signatures