A long life of excess: The interacting transient SN 2017hcc

TL;DR

This paper reports a five-year observational study of the long-lived type IIn supernova SN 2017hcc, revealing its interaction with dense circumstellar material, slow evolution, and dust formation processes.

Contribution

It provides the first detailed long-term follow-up of SN 2017hcc, highlighting its unique interaction with CSM and dust evolution over five years.

Findings

Long rise time and high luminosity indicate strong ejecta-CSM interaction.

Infrared excess suggests dust formation and light echo effects.

Spectral blueshifts diminish over time, indicating changing ejecta dynamics.

Abstract

In this study we present the results of a five-year follow-up campaign of the long-lived type IIn supernova SN 2017hcc, found in a spiral dwarf host of near-solar metallicity. The long rise time (57 $\pm$ 2 days, ATLAS $o$ band) and high luminosity (peaking at $-$20.78 $\pm$ 0.01 mag in the ATLAS $o$ band) point towards an interaction of massive ejecta with massive and dense circumstellar material (CSM). The evolution of SN 2017hcc is slow, both spectroscopically and photometrically, reminiscent of the long-lived type IIn, SN 2010jl. An infrared (IR) excess was apparent soon after the peak, and blueshifts were noticeable in the Balmer lines starting from a few hundred days, but appeared to be fading by around +1200 days. We posit that an IR light echo from pre-existing dust dominates at early times, with some possible condensation of new dust grains occurring at epochs >$\sim$+800 days.