# The aspherical explosion of the Type IIP SN 2017gmr

## TL;DR

This paper reports an early polarization rise in SN 2017gmr, revealing extensive asymmetry in its explosion structure, which challenges existing models of core-collapse supernovae.

## Contribution

It presents the first observation of early polarization rise in a Type IIP supernova, indicating highly extended asphericity in the explosion structure.

## Key findings

- SN 2017gmr shows polarization rise 30 days before tail phase
- Asymmetries extend to outer hydrogen envelope
- Reveals intrinsic diversity in core-collapse supernova geometries

## Abstract

Type IIP supernovae (SNe IIP), which represent the most common class of core-collapse (CC) SNe, show a rapid increase in continuum polarization just after entering the tail phase. This feature can be explained by a highly asymmetric helium core, which is exposed when the hydrogen envelope becomes transparent. Here we report the case of a SN IIP (SN~2017gmr) that shows an unusually early rise of the polarization, $\gtrsim 30$ days before the start of the tail phase. This implies that SN~2017gmr is an SN IIP that has very extended asphericity. The asymmetries are not confined to the helium core, but reach out to a significant part of the outer hydrogen envelope, hence clearly indicating a marked intrinsic diversity in the aspherical structure of CC explosions. These observations provide new constraints on the explosion mechanism, where viable models must be able to produce such extended deviations from spherical symmetry, and account for the observed geometrical diversity.