The bright long-lived Type II SN 2021irp powered by aspherical circumstellar material interaction (II): Estimating the CSM mass and geometry with polarimetry and light curve modeling

TL;DR

This study investigates the properties of the circumstellar material around the Type II supernova 2021irp, revealing an aspherical, massive CSM disk through polarimetry and light curve modeling, shedding light on stellar mass ejection processes.

Contribution

It provides the first detailed polarimetric and light curve modeling analysis of SN 2021irp, estimating the CSM mass and geometry, and proposing a binary interaction origin for the CSM disk.

Findings

SN 2021irp shows high intrinsic polarization (~0.8%), indicating an aspherical CSM interaction.

The CSM mass is estimated to be greater than 2 solar masses.

The CSM is modeled as a disk with a mass-loss rate of 0.035-0.1 M_sun/yr and a half-opening angle of 30-50 degrees.

Abstract

There is evidence for interaction between supernova (SN) ejecta and massive circumstellar material (CSM) in various types of SNe. The mass-ejection mechanisms that produce massive CSM are unclear, and studying interacting SNe and their CSM can shed light on these mechanisms and the final stages of stellar evolution. We aim to study the properties of the CSM in the bright, long-lived, hydrogen-rich (Type II) SN 2021irp, which is interacting with a massive aspherical CSM. We present imaging- and spectro-polarimetric observations of SN 2021irp. By modelling its polarisation and bolometric light curve, we derive the mass and distribution of the CSM. SN 2021irp shows a high intrinsic polarisation of $\sim0.8$%. This high continuum polarisation suggests an aspherical photosphere created by an aspherical CSM interaction. Based on the bolometric light curve evolution and the high polarization, SN 2021irp can be explained as a typical Type II SN interacting with a CSM disk with a corresponding mass-loss rate and half-opening angle of $\sim0.035$ - $0.1$ M$_{\odot}$ yr$^{-1}$ and $\sim30$ - $50^{\circ}$, respectively. The total CSM mass derived is $\gtrsim 2$ M$_{\odot}$. We suggest that this CSM disk was created by some process related to binary interaction, and that SN 2021irp is the end product of a typical massive star (i.e. with Zero-Age-Main-Sequence mass of $\sim 8-18$ M$_{\odot}$) that has a separation and/or mass ratio with its companion star that led to an extreme mass ejection within decades of explosion. Based on the observational properties of SN 2021irp and similar SNe, we propose a general picture for the spectroscopic properties of Type II SNe interacting with a massive disk CSM.