The peculiar Type Ia supernova iPTF14atg: Chandrasekhar-mass explosion or violent merger? (1604.05730v1)

Abstract: iPTF14atg, a subluminous peculiar Type Ia supernova (SN Ia) similar to SN 2002es, is the first SN Ia for which a strong UV flash was observed in the early-time light curves. This has been interpreted as evidence for a single-degenerate (SD) progenitor system where such a signal is expected from interactions between the SN ejecta and the non-degenerate companion star. Here, we compare synthetic observables of multi-dimensional state-of-the-art explosion models for different progenitor scenarios to the light curves and spectra of iPTF14atg. From our models, we have difficulties explaining the spectral evolution of iPTF14atg within the SD progenitor channel. In contrast, we find that a violent merger of two carbon-oxygen white dwarfs with 0.9 and 0.76 solar masses, respectively, provides an excellent match to the spectral evolution of iPTF14atg from 10d before to several weeks after maximum light. Our merger model does not naturally explain the initial UV flash of iPTF14atg. We discuss several possibilities like interactions of the SN ejecta with the circum-stellar medium and surface radioactivity from a He ignited merger that may be able to account for the early UV emission in violent merger models.

Insights into the Nature of Peculiar Type Ia Supernova iPTF14atg: A Comprehensive Model Comparison

The paper by M. Kromer et al. titled "The peculiar Type Ia supernova iPTF14atg: Chandrasekhar-mass explosion or violent merger?" offers a detailed examination of the peculiar Type Ia supernova (SN Ia) iPTF14atg, which presents unique challenges to conventional supernova models. This paper evaluates the progenitor scenarios and explosion mechanisms to elucidate the nature of iPTF14atg by comparing state-of-the-art theoretical models with observations.

Key Observations and Claims

iPTF14atg, discovered in the galaxy IC 831, garnered attention due to its subluminous nature and distinctive early-time UV flash detected in its light curves. This UV emission was initially hypothesized to result from interaction between the SN ejecta and a companion star in a single-degenerate (SD) progenitor system. The authors conduct a comprehensive analysis using synthetic observables from multidimensional explosion models to test this hypothesis against alternative scenarios, such as a double-degenerate (DD) progenitor channel.

The paper emphasizes several critical observations:

• Difficulty in reconciling the spectral evolution of iPTF14atg within the traditional SD progenitor framework.
• The violent merger of two carbon-oxygen white dwarfs (CO WDs) with masses of 0.9 and 0.76 M☉ respectively, emerges as a promising model.
• This merger scenario aligns with the spectral evolution of iPTF14atg from 10 days before maximum light to several weeks post-maximum but does not naturally account for the initial UV flash.

Theoretical Implications

The investigation highlights the ongoing debate around SN Ia progenitors, traditionally dividing scenarios into SD and DD categories. The analysis of iPTF14atg contributes to this discourse by challenging established models and proposing adaptations in the violent merger framework. The match of synthetic observables to iPTF14atg characteristics provides compelling evidence for DD scenarios in certain subluminous SNe Ia, such as iPTF14atg, although the enigmatic early UV flash remains unresolved.

The implications of these findings are significant:

1. Progenitor Diversity: Suggests the necessity of broad consideration of progenitor systems beyond the conventional Chandrasekhar-mass models. High-resolution merger models could reveal nuances in surface radioactivity and CSM interactions impacting early-time features.
2. Surface Radioactivity and Circum-Stellar Interaction: Calls for future simulations to explore non-spherically symmetric CSM configurations or He ignited mergers that might shed light on the preliminary UV emissions observed in iPTF14atg.

Conclusion and Future Directions

The paper asserts that while current models struggle to encapsulate the full spectrum of iPTF14atg's properties, modifications to the DD merger theory, particularly considering low metallicity impacts, hold promising potential. Further investigations are advocated, requiring enhanced hydrodynamic and radiative transfer modeling to account for asymmetric geometries and interactions in SN Ia explosions.

As diverse SN characteristics continue to emerge, this research underscores the complexity inherent in supernova progenitor scenarios and the consequences for cosmological distance measurements. The exploration of 2002es-like supernovae through such detailed theoretical scrutiny paves the way for future advancements in astrophysical modeling and understanding of stellar evolution dynamics.