Puzzle of [Ar II] 7 mcm line broad component of SN 1987A

TL;DR

This paper investigates the origin of the broad [Ar II] 7 μm line component in SN 1987A, proposing dust scattering and proton ionization as key factors influencing the line profile and emission characteristics.

Contribution

It introduces a model explaining the broad line wings through dust scattering and ionization effects, providing new insights into the ejecta's physical conditions.

Findings

Line broadening explained by dust scattering with specific grain sizes.

Red wing flux excess attributed to scattering off optically thin dust.

Additional heating possibly due to ionization losses of relativistic protons.

Abstract

We explore the origin of the broad component of the [Ar II] 7 mcm line emission related to the ejecta excitation by the neutron star of SN 1987A. We argue that the line broad wings are emitted at the tmperature of $\sim300$ K. The flux excess in the red wing of [Ar II] line is reproduced by the line photons scattering off the optically thin uniform dust component with the grain size of 1 - 2 mcm and the total mass of $\mbox{(several)}\times10^{-3}\,M{\odot}$. The dusty opaque clumps containing almost all the dust of SN~1987A have a low occultation optical depth and line photon scattering on dusty clumps do not contribute noticeably in the red wing. The additional heating might be related to ionization losses of relativistic protons.