Fading Echoes of Interaction: Probing Centuries of Preexplosion Mass-Loss in Four Type IIn Supernovae

TL;DR

This study uses late-time X-ray and radio data of four Type IIn supernovae to reveal that their progenitors experienced lower mass-loss rates over centuries before explosion than previously estimated from optical data, indicating rapid progenitor evolution.

Contribution

It provides new constraints on pre-supernova mass-loss rates of Type IIn supernovae using late-time X-ray and radio observations, highlighting discrepancies with earlier optical estimates.

Findings

Mass-loss rates are 1-2 orders of magnitude lower than optical estimates.

Detected spectral inversion in KISS15s radio SED suggests a secondary shock or pulsar wind.

Progenitors experienced rapidly evolving mass-loss rates over centuries before explosion.

Abstract

Supernovae characterized by enduring narrow optical hydrogen emission lines (SNe IIn) are believed to result primarily from the core-collapse of massive stars undergoing sustained interaction with a dense circumstellar medium (CSM). While the properties of SN IIn progenitors have relatively few direct constraints, the ongoing ejecta-CSM interaction provides unique information about late-stage stellar mass-loss preceding core-collapse. We present late-time X-ray and radio observations of four $\geq$3000 day-old SNe IIn: SN 2013L, SN 2014ab, SN 2015da, and KISS15s. The radio and X-ray emission from KISS15s indicate a mass-loss rate of \eq{\dot M\sim4\times 10^{-3}~\rm{M_{\odot}\,yr^{-1}}} at $\sim$450 years pre-supernova -- 2 orders of magnitude below earlier optical estimates (which probed the mass loss immediately preceding the supernova). We find hints of a spectral inversion in the radio SED of KISS15s; a possible signature of a secondary shock due to a binary system or the emergence of a pulsar wind. For SN 2013L, we obtain a mass-loss rate of \eq{\dot M\sim2 \times 10^{-3}~\rm{M_{\odot}\,yr^{-1}}} at $\sim$400 years pre-explosion based on the X-ray detection. For SN 2014ab and SN 2015da, we find a upper limits on the mass-loss rates of \eq{\dot M<2\times10^{-3}~M_{\sun}\,yr^{-1}} explosion at $\sim$300 and 250 years pre-explosion, respectively. All four objects display mass-loss rates lower than estimates from earlier optical analyses by at least 1-2 orders of magnitude, necessitating a rapidly evolving progenitor process over the last centuries pre-explosion. Our analysis reveals how X-ray and radio observations can elucidate progenitor evolution when these objects have faded at optical wavelengths.