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Classical novae are thermonuclear explosions that occur on the surfaces ofwhite dwarf stars in interacting binary systems (Bode & Evans 2008). It haslong been thought that the luminosity of classical novae is powered bycontinued nuclear burning on the surface of the white dwarf after the initialrunaway (Gallaher & Starrfield 1978). However, recent observations of GeV$\gamma$-rays from classical novae have hinted that shocks internal to the novaejecta may dominate the nova emission. Shocks have also been suggested to powerthe luminosity of events as diverse as stellar mergers (Metzger & Pejcha 2017),supernovae (Moriya et al. 2018), and tidal disruption events (Roth et al.2016), but observational confirmation has been lacking. Here we reportsimultaneous space-based optical and $\gamma$-ray observations of the 2018 novaV906 Carinae (ASASSN-18fv), revealing a remarkable series of distinctcorrelated flares in both bands. The optical and $\gamma$-ray flares occursimultaneously, implying a common origin in shocks. During the flares, the novaluminosity doubles, implying that the bulk of the luminosity is shock-powered.Furthermore, we detect concurrent but weak X-ray emission from deeply embeddedshocks, confirming that the shock power does not appear in the X-ray band andsupporting its emergence at longer wavelengths. Our data, spanning the spectrumfrom radio to $\gamma$-ray, provide direct evidence that shocks can powersubstantial luminosity in classical novae and other optical transients.

Direct evidence for shock-powered optical emission in a nova