Mid-Infrared Dust Evolution and Late-time Circumstellar Medium Interaction in SN 2017eaw

TL;DR

Six years after explosion, SN 2017eaw shows stable mid-infrared dust emission and ongoing circumstellar medium interaction, indicating the presence of pre-existing dust rather than newly formed dust in the ejecta.

Contribution

This study provides the first detailed mid-infrared analysis of SN 2017eaw years after explosion, revealing stable dust properties and ongoing CSM interaction.

Findings

Detection of persistent cool dust component at 160 K with no evolution over a year.

Continued CSM-ejecta interaction observed in UV and IR emissions beyond 2000 days.

Evidence suggests the dust is primarily pre-existing rather than newly formed.

Abstract

We present JWST/MIRI and complementary ground-based near-infrared observations of the Type II SN 2017eaw taken 6 years post-explosion. SN 2017eaw is still detected out to 25 $\mu$m and there is minimal evolution in the mid-infrared spectral energy distribution (SED) between the newly acquired JWST/MIRI observations and those taken a year earlier. Modeling of the mid-infrared SED reveals a cool $\sim$160 K dust component of $5.5\times10^{-4}\ \mathrm{M}_\odot$ and a hot $\sim$1700 K component of $5.4\times10^{-8}\ \mathrm{M}_\odot$ both composed of silicate dust. Notably there is no evidence of temperature or mass evolution in the cool dust component in the year between JWST observations. We also present new and archival HST and ground-based ultraviolet (UV) and optical observations which reveal reduced but continued circumstellar medium (CSM)-ejecta interaction at $>$2000 days post-explosion. The UV and mid-infrared emission show similar decline rates, suggesting both probe the interface between the ejecta and CSM. Given this, the continued existence of boxy H$\alpha$ emission in the nebular spectra, the low inferred optical depth of the dust, and the lack of temperature and mass evolution, we suggest that the cool dust component in SN 2017eaw may be primarily due to pre-existing dust rather than newly-formed dust in the ejecta or cold dense shell.