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 similar to 300 000 L-circle dot red supergiant progenitor underwent an outburst in 2009 and has since disappeared in the optical. In the LBT data from 2008 May through 2019 October, the upper limit on any increase in the R-band luminosity of the source is 2000 L-circle dot. 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 2015 October and 2017 September to 2900 L-circle dot 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, but the post-failure phenomenology requires further theoretical study.

Automated summary

New data from the Large Binocular Telescope, Hubble Space Telescope, and Spitzer Space Telescope are presented for the failed supernova candidate N6946-BH1. Attempts to detect the candidate with Chandra were unsuccessful. Observations show that the source disappeared in optical, and continued to fade in near-IR and mid-IR, suggesting a failed supernova, but the post-failure phenomenology requires further theoretical study.