Low R_v from circumstellar dust around supernovae

TL;DR

This study uses Monte-Carlo simulations to analyze how circumstellar dust affects the extinction law around supernovae, revealing a lower R_v value consistent with observations of Type Ia supernova colors.

Contribution

It provides a detailed simulation-based analysis of circumstellar dust's impact on supernova light extinction, highlighting the semi-diffusive propagation and resulting low R_v values.

Findings

Typical R_v values of 1.5-2.5 from simulations

Steepening of extinction law toward near-UV

Consistency with observed supernova color data

Abstract

The effective extinction law for supernovae surrounded by circumstellar dust is examined by Monte-Carlo simulations. Grains with light scattering properties as for interstellar dust in the Milky-Way (MW) or the Large Magellanic Clouds (LMC), but surrounding the explosion site would cause a semi-diffusive propagation of light up to the edge of the dust shell. Multiple scattering of photons predominantly attenuates photons with shorter wavelengths, thus steepening the effective extinction law as compared to the case of single scattering in the interstellar medium. Our simulations yield typical values for the total to selective extinction ratio $R_V\sim 1.5-2.5$, as seen in recent studies of Type Ia supernova colors, with further stiffening differential extinction toward the near-UV.