Did the progenitor of SN2011dh have a binary companion?

TL;DR

Late-time HST observations of SN 2011dh reveal a faint source inconsistent with a stellar origin, suggesting the progenitor's binary companion is not clearly detected, and the light curve has plateaued post-explosion.

Contribution

This study provides the first late-time UV and optical observations of SN 2011dh, clarifying the nature of the progenitor and its potential binary companion.

Findings

The late-time source is fainter than the pre-explosion progenitor.

The light curve has plateaued at all wavelengths.

The SED is inconsistent with a stellar source.

Abstract

We present late-time Hubble Space Telescope (HST) ultraviolet (UV) and optical observations of the site of SN 2011dh in the galaxy M51, ~1164 days post-explosion. At the SN location, we observe a point source that is visible at all wavelengths, that is significantly fainter than the spectral energy distribution (SED) of the Yellow Supergiant progenitor observed prior to explosion. The previously reported photometry of the progenitor is, therefore, completely unaffected by any sources that may persist at the SN location after explosion. In comparison with the previously reported late-time photometric evolution of SN 2011dh, we find that the light curve has plateaued at all wavelengths. The SED of the late-time source is clearly inconsistent with a SED of stellar origin. Although the SED is bright at UV wavelengths, there is no strong evidence that the late-time luminosity originates solely from a stellar source corresponding to the binary companion, although a partial contribution to the observed UV flux from a companion star can not be ruled out.