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The failed supernova N6946-BH1 likely formed a black hole (BH); we age-datethe surrounding population and infer an age and initial mass for the progenitorof this BH formation candidate. First, we use archival Hubble Space Telescopeimaging to extract broadband photometry of the resolved stellar populationssurrounding this event. Using this photometry, we fit stellar evolution modelsto the color-magnitude diagrams to measure the recent star formation history(SFH). Modeling the photometry requires an accurate distance; therefore, wemeasure the tip of the red giant branch (TRGB) and infer a distance modulus of$29.47 \pm 0.079$ to NGC~6946, or a metric distance of $7.83 \pm 0.29$ Mpc. Toestimate the stellar population's age, we convert the SFH and uncertaintiesinto a probabilistic distribution for the progenitor's age. The region in theimmediate vicinity of N6946-BH1 exhibits the youngest and most vigorous starformation for several hundred pc. This suggests that the progenitor is not arunaway star. From these measurements, we infer an age for the BH progenitor of$10.6^{+14.5}_{-5.9}$ Myr. Assuming that the progenitor evolved effectively asa single star, this corresponds to an initial mass of $17.9^{+29.9}_{-7.6}$$M_{\odot}$. Previous spectral energy distribution (SED) modeling of theprogenitor suggests a mass of $\sim$27 $M_{\odot}$. Formally, the SED-derivedmass falls within our narrowest 68\% confidence interval; however, $91\%$ ofthe probability distribtuion function we measure lies below that mass, puttingsome tension between the age and the direct-imaging results.

The Progenitor Age and Mass of the Black-Hole-Formation Candidate N6946-BH1