Diagnosis of Circumstellar Matter Structure in Interaction-powered Supernovae with Hydrogen Line Feature

TL;DR

This paper uses radiative transfer simulations to link supernova spectral line shapes with the structure of surrounding circumstellar matter, helping to identify the mass-loss mechanisms shaping supernova environments.

Contribution

It introduces a method to distinguish steady from eruptive mass loss in supernovae by analyzing hydrogen line features in their spectra.

Findings

Narrow P-Cyg lines indicate eruptive mass loss.

Blue-shifted photon excess relates to shock velocity.

Spectroscopic diagnostics can reveal CSM formation mechanisms.

Abstract

Some supernovae (SNe) are powered by collision of the SN ejecta with a dense circumstellar matter (CSM). Their emission spectra show characteristic line shapes of combined broad emission and narrow P-Cyg lines, which should closely relate to the CSM structure and the mass-loss mechanism that creates the dense CSM. We quantitatively investigate the relationship between the line shape and the CSM structure by Monte Carlo radiative transfer simulations, considering two representative cases of dense CSM formed by steady and eruptive mass loss. Comparing the H$\alpha$ emission between the two cases, we find that a narrow P-Cyg line appears in the eruptive case while it does not appear in the steady case, due to the difference in the velocity gradient in the dense CSM. We also reproduce the blue-shifted photon excess observed in some Type IIn SNe, which is formed by photon transport across the shock wave and find the relationship between the velocity of the shocked matter and the amount of the blue shift of the photon excess. We conclude that the presence or absence of narrow P-Cyg lines can distinguish the mass loss mechanism, and suggest high-resolution spectroscopic observations with $\lambda/ \Delta \lambda \gtrsim 10^4$ after the light curve peak for applying this diagnostic method.