# Evidence for bipolar explosions in Type IIP supernovae

**Authors:** T. Nagao, K. Maeda, S. Mattila, H. Kuncarayakti, M. Kawabata, K. Taguchi, T. Nakaoka, A. Cikota, M. Bulla, S. Vasylyev, C. P. Gutierrez, M. Yamanaka, K. Isogai, K. Uno, M. Ogawa, S. Inutsuka, M. Tsurumi, R. Imazawa, K. S. Kawabata  
**arXiv:** [2406.14057](https://arxiv.org/abs/2406.14057)  
**Date:** 2024-06-20  
**Summary page:** https://www.summarizepaper.com/en/paper/2406.14057v1/

## Key points

- Recent observations of core-collapse supernovae have shown the presence of aspherical explosions, emphasizing the need to understand globally aspherical structures in these events.
- The study by T. Nagao et al. focused on Type IIP SN 2021yja and compared its findings with other Type IIP SNe known for large-scale aspherical structures in their hydrogen envelopes (SNe 2012aw, 2013ej, and 2017gmr).
- High continuum polarization was observed during the plateau phase of SNe 2012aw and 2021yja, suggesting a bipolar explosion scenario with polar and equatorial components within the SN ejecta.
- The dominance of an aspherical axis created by the polar ejecta was noted early on, while a perpendicular axis along the equatorial ejecta emerged later stages after the receding of the photosphere in the polar ejecta.
- Additional observational properties, including time evolution of line velocities and shapes in nebular spectra, supported the interpretation of bipolar explosions in SNe 2012aw and 2021yja.

## Summary

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Recent observations of core-collapse supernovae (SNe) have revealed the presence of aspherical explosions, highlighting the importance of understanding globally aspherical structures in these explosive events. However, the specific geometries of these explosions, from the inner cores to the outer envelopes, remain poorly understood. In a recent study by T. Nagao et al., various observational techniques were used to investigate the Type IIP SN 2021yja and compare its findings with other Type IIP SNe known for their large-scale aspherical structures in their hydrogen envelopes, such as SNe 2012aw, 2013ej, and 2017gmr. During the plateau phase of SNe 2012aw and 2021yja, high continuum polarization was observed with two components displaying perpendicular polarization angles. This unique behavior led researchers to propose a bipolar explosion scenario for these supernovae. According to this model, the explosion is composed of a polar component (energetic) and an equatorial component (bulk) within the SN ejecta. The dominance of an aspherical axis created by the polar ejecta was noted during early phases, while a perpendicular axis along the equatorial ejecta emerged at later stages after the receding of the photosphere in the polar ejecta. The interpretation of bipolar explosions in SNe 2012aw and 2021yja was further supported by additional observational properties, including time evolution of line velocities and shapes in nebular spectra. Furthermore, polarization data from other Type IIP SNe exhibiting large-scale aspherical structures in their hydrogen envelopes (SNe 2013ej and 2017gmr) also aligned with this bipolar-explosion scenario. This comprehensive study conducted by Nagao et al., involving multiple observational techniques and comparisons with similar supernovae events, provides valuable insights into understanding complex explosion geometries in core-collapse supernovae. The findings contribute significantly to advancing our knowledge of supernova dynamics and may pave the way for further research into unraveling the mysteries surrounding these powerful cosmic events.