The search for failed supernovae with the Large Binocular Telescope: confirmation of a disappearing star

We present Hubble Space Telescope imaging confirming the optical disappearance of the failed supernova (SN) candidate identified by Gerke et al. (2015). This \(\sim 25~M_{\odot}\) red supergiant experienced a weak \(\sim 10^{6}~L_{\odot}\) optical outburst in 2009 and is now at least 5 magnitudes fainter than the progenitor in the optical. The mid-IR flux has slowly decreased to the lowest levels since the first measurements in 2004. There is faint (\(2000-3000~L_{\odot}\)) near-IR emission likely associated with the source. We find the late-time evolution of the source to be inconsistent with obscuration from an ejected, dusty shell. Models of the spectral energy distribution indicate that the remaining bolometric luminosity is \(>6\) times fainter than that of the progenitor and is decreasing as \(\sim t^{-4/3}\). We conclude that the transient is unlikely to be a SN impostor or stellar merger. The event is consistent with the ejection of the envelope of a red supergiant in a failed SN and the late-time emission could be powered by fallback accretion onto a newly-formed black hole. Future IR and X-ray observations are needed to confirm this interpretation of the fate for the star.