Supernova explosions interacting with aspherical circumstellar material: implications for light curves, spectral line profiles, and polarization

TL;DR

This study uses 2D hydrodynamic simulations to explore how supernova ejecta interacting with aspherical circumstellar material affect observable features like light curves, spectral lines, and polarization, revealing diverse signatures based on CSM geometry.

Contribution

It provides detailed modeling of supernova interactions with various aspherical CSM structures, linking hydrodynamical phenomena to observable signatures and aiding interpretation of complex supernova observations.

Findings

Shock interactions cause fluctuating shock heating power.

Circumstellar disks and bipolar lobes produce high polarization and symmetric line profiles.

Colliding wind shells lead to asymmetric, evolving spectral lines with low polarization.

Abstract

Some supernova (SN) explosions show evidence for interaction with pre-existing non-spherically symmetric circumstellar medium (CSM) in their light curves, spectral line profiles, and polarization signatures. To better understand the connection with binary stars and to aid in the interpretation of observations, we perform two-dimensional axisymmetric hydrodynamic simulations where an expanding spherical SN ejecta initialized with realistic density and velocity profiles collide with various aspherical CSM distributions. We consider CSM in the form of a circumstellar disk, colliding wind shells in binary stars with different orientations and distances from the SN progenitor, and bipolar lobes representing a scaled down version of the Homunculus nebula of $\eta$~Car. We study how our simulations map onto observables, including approximate light curves, indicative spectral line profiles at late times, and estimates of polarization signature. We find that the SN--CSM collision layer is composed of normal and oblique shocks, reflected waves, and other hydrodynamical phenomena that lead to acceleration and shear instabilities. As a result, the total shock heating power fluctuates in time, although the emerging light curve might be smooth if the shock interaction region is deeply embedded in the SN envelope. SNe with circumstellar disks or bipolar lobes exhibit late-time spectral line profiles symmetric with respect to the rest velocity and relatively high polarization. In contrast, SNe with colliding wind shells naturally lead to line profiles with asymmetric and time-evolving blue and red wings and low polarization. Given the high frequency of binaries among massive stars, interaction of SN ejecta with a pre-existing colliding wind shell must occur and the observed signatures could be used to characterize the binary companion.