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We present Hubble Space Telescope (HST) imaging of the site of SN 2015bh inthe nearby spiral galaxy NGC 2770 taken between 2017 and 2019, nearly fouryears after the peak of the explosion. In 2017-2018, the transient fadessteadily in optical filters before declining more slowly to $F814W = -7.1$ magin 2019, $\approx$4 mag below the level of its eruptive luminous blue variable(LBV) progenitor observed with HST in 2008-2009. The source fades at a constantcolor of $F555W - F814W = 0.4$ mag until 2018, similar to SN 2009ip andconsistent with a spectrum dominated by interaction of the ejecta withcircumstellar material (CSM). A deep optical spectrum obtained in 2021 lackssignatures of ongoing interaction ($L_{\mathrm{H}\alpha} \lesssim 10^{38}$ ergs$^{-1}$ for broadened emission $\lesssim$2000 km s$^{-1}$), but indicates thepresence of a nearby H II region ($\lesssim$300 pc). The color evolution of thefading source makes it unlikely that emission from a scattered-light echo orbinary OB companion of the progenitor contributes significantly to theflattening of the late-time light curve. The remaining emission in 2019 mayplausibly be attributed an evolved/inflated companion or an unresolved($\lesssim$3 pc), young stellar cluster. Importantly, the color evolution of SN2015bh rules out scenarios in which the surviving progenitor is obscured bynascent dust and does not clearly indicate a transition to a hotter, opticallyfaint state. The simplest explanation is that the massive progenitor did notsurvive. SN 2015bh likely represents a remarkable example of the terminalexplosion of a massive star preceded by decades of end-stage eruptivevariability.

Hubble Space Telescope Imaging Reveals That SN 2015bh Is Much Fainter than Its Progenitor