Unveiling the Nature of SN 2011fh: a Young and Massive Star Gives Rise to a Luminous SN 2009ip-like Event

TL;DR

This study presents a decade of observations of SN 2011fh, revealing it as a young, massive star undergoing energetic outbursts, with spectral and photometric features similar to SN 2009ip, and suggests super-Eddington winds as a mass-loss mechanism.

Contribution

It provides detailed observational evidence linking SN 2011fh to a young, massive star with super-Eddington winds, advancing understanding of luminous blue variable-like supernova progenitors.

Findings

SN 2011fh exhibited multiple brightening events with spectra dominated by Balmer lines.

Progenitor estimated to be a 35-80 M_sun star, likely a luminous blue variable.

Progenitor exceeded the Eddington limit prior to outburst, indicating strong super-Eddington winds.

Abstract

In recent years, many Type IIn supernovae have been found to share striking similarities with the peculiar SN 2009ip, whose true nature is still under debate. Here, we present 10 years of observations of SN 2011fh, an interacting transient with spectroscopic and photometric similarities to SN 2009ip. SN 2011fh had a M$_r \sim -16$ mag brightening event, followed by a brighter M$_r \sim -18$ mag luminous outburst in August 2011. The spectra of SN 2011fh are dominated by narrow to intermediate Balmer emission lines throughout its evolution, with P Cygni profiles indicating fast-moving material at $\sim 6400 \ \textrm{km s}^{-1}$. HST/WFC3 observations from October of 2016 revealed a bright source with M$_{F814W} \approx -13.3$ mag, indicating that we are seeing the ongoing interaction of the ejecta with the circumstellar material or that the star might be going through an eruptive phase five years after the luminous outburst of 2011. Using HST photometry of the stellar cluster around SN 2011fh, we estimated an age of $\sim 4.5$ Myr for the progenitor, which implies a stellar mass of $\sim 60$ M$_\odot$, using single-star evolution models, or a mass range of $35 - 80 \ \textrm{M}_\odot$, considering a binary system. We also show that the progenitor of SN 2011fh exceeded the classical Eddington limit by a large factor in the months preceding the luminous outburst of 2011, suggesting strong super-Eddington winds as a possible mechanism for the observed mass-loss. These findings favor an energetic outburst in a young and massive star, possibly a luminous blue variable.