Abundance tomography of Type Iax SN 2011ay with tardis

Abstract We present a detailed spectral analysis of Type Iax SN 2011ay. Our spectra cover epochs between −3 and +19 d with respect to the maximum light in B band. This time range allows us to employ a so-called abundance tomography technique. The synthetic spectral fitting was made with the 1D Monte Carlo radiative transfer code tardis. In this paper, we describe our method to fit multiple epochs with a self-consistent, stratified atmospheric model. We compare our results to previously published syn++ models and the predictions of different explosion scenarios. Using a fixed density profile (exponential fit of W7), we find that a uniform abundance model cannot reproduce the spectral features before maximum light because of the emergence of excessively strong Fe lines. In our best-fitting tardis model, we find an abundance profile that separated into two different regimes: a well-mixed region under 10 000 km s−1 and a stratified region with decreasing IGE abundances above 10 000 km s−1. Based on a detailed comparative analysis, our conclusion is that the available pure deflagration models cannot fully explain either the observed properties of SN 2011ay or the results of our tardis modelling. Further examinations are necessary to find an adequate explanation for the origin of this object.