The Search for Failed Supernovae with the Large Binocular Telescope:
  N6946-BH1, Still No Star
  We present new Large Binocular Telescope, Hubble Space Telescope, and Spitzer
Space Telescope data for the failed supernova candidate N6946-BH1. We also
report an unsuccessful attempt to detect the candidate with Chandra. The
~300,000 Lsun red supergiant progenitor underwent an outburst in 2009 and has
since disappeared in the optical. In the LBT data from May 2008 through October
2019, the upper limit on any increase in the R-band luminosity of the source is
2000 Lsun. HST and Spitzer observations show that the source continued to fade
in the near-IR and mid-IR, fading by approximately a factor of 2 between
October 2015 and September 2017 to 2900 Lsun at H band (F160W). Models of the
spectral energy distribution are inconsistent with a surviving star obscured
either by an ongoing wind or dust formed in the transient. The disappearance of
N6946-BH1 remains consistent with a failed supernova.
