Puzzle of [Ar II] 7 \(\mu\)m Line Broad Component of SN 1987A

Abstract

We explore the origin of the broad component of the [Ar II] 7 \(\mu\)m 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 temperature of \({\sim}300\) 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 \(\mu\)m and the total mass of \(\textrm{(several)}\times 10^{-3}\)  \(M_{\odot}\). 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.