Evidence for late-time dust formation in the ejecta of supernova SN~1995N from emission-line asymmetries

TL;DR

This study provides evidence for late-time dust formation in supernova SN 1995N's ejecta, based on emission-line asymmetries and infrared observations, suggesting dust formed hundreds of days post-explosion.

Contribution

It presents the first detailed evidence of dust formation occurring significantly later than typical in a supernova, revising the estimated explosion date accordingly.

Findings

Infrared emission at 14-15 years is due to newly formed dust, not an echo.

Spectral line asymmetries indicate dust absorption within ejecta.

Approximately 0.4 solar masses of amorphous carbon dust are present.

Abstract

We present a study of the dust associated with the core-collapse supernova SN~1995N. Infrared emission detected 14--15 years after the explosion was previously attributed to thermally echoing circumstellar material associated with the SN progenitor. We argue that this late-time emission is unlikely to be an echo, and is more plausibly explained by newly formed dust in the supernova ejecta, indirectly heated by the interaction between the ejecta and the CSM. Further evidence in support of this scenario comes from emission line profiles in spectra obtained 22 years after the explosion; these are asymmetric, showing greater attenuation on the red wing, consistent with absorption by dust within the expanding ejecta. The spectral energy distribution and emission line profiles at epochs later than $\sim$5000 days are both consistent with the presence of about 0.4~M$_\odot$ of amorphous carbon dust. The onset of dust formation is apparent in archival optical spectra, taken between 700 and 1700 days after the assumed explosion date. As this is considerably later than most other instances where the onset of dust formation has been detected, we argue that the explosion date must be later than previously assumed.