Very Late-Time JWST and Keck Spectra of the Oxygen-Rich Supernova 1995N

TL;DR

This paper presents late-time JWST and Keck spectra of supernova 1995N, revealing ongoing dust emission, changes in dust properties, and unusual oxygen lines indicating a transition from supernova to remnant.

Contribution

It provides the earliest infrared spectra of SN 1995N over 10,000 days post-explosion, showing dust evolution and spectral changes indicative of a supernova remnant transition.

Findings

Dust heating persists but is reduced since 2009/2010.

Dust mass may have increased or heating source decreased.

Unusually strong oxygen forbidden lines suggest a transition to a supernova remnant.

Abstract

We present new {\it JWST}/MIRI MRS and Keck spectra of SN 1995N obtained in 2022--2023, more than 10,000 days after the supernova (SN) explosion. These spectra are among the latest direct detections of a core-collapse SN, both through emission lines in the optical and thermal continuum from infrared dust emission. The new infrared data show that dust heating from radiation produced by the ejecta interacting with circumstellar matter is still present, but greatly reduced from when SN 1995N was observed by the {\it Spitzer Space Telescope} and {\it WISE} in 2009/2010 and 2018, when the dust mass was estimated to be 0.4 M(Sun). New radiative-transfer modeling suggests that the dust mass and grain size may have increased between 2010 and 2023. The new data can alternatively be well fit with a dust mass of 0.4 M(Sun) and a much reduced heating source luminosity. The new late-time spectra show unusually strong oxygen forbidden lines, stronger than the H-alpha emission. This indicates that SN 1995N may have exploded as a stripped-envelope SN which then interacted with a massive H-rich circumstellar shell, changing it from intrinsically Type Ib/c to Type IIn. The late-time spectrum results when the reverse shock begins to excite the inner H-poor, O-rich ejecta. This change in the spectrum is rarely seen, but marks the start of the transition from SN to SN remnant.