The Search for Failed Supernovae with the Large Binocular Telescope: N6946-BH1, Still No Star

TL;DR

This study uses multi-wavelength observations to investigate the failed supernova candidate N6946-BH1, finding no evidence of a surviving star and supporting its classification as a failed supernova.

Contribution

It provides new observational data and analysis that strengthen the case for N6946-BH1 being a failed supernova, with no detectable surviving star in optical or infrared wavelengths.

Findings

No increase in optical luminosity after 2009

Source faded in near-IR and mid-IR, indicating no surviving star

Spectral energy distribution models are inconsistent with a surviving star

Abstract

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.