Direct evidence for shock-powered optical emission in a nova

Abstract

Classical novae are thermonuclear explosions that occur on the surfaces of white dwarf stars in interacting binary systems(1). It has long been thought that the luminosity of classical novae is powered by continued nuclear burning on the surface of the white dwarf after the initial runaway(2). However, recent observations of gigaelectronvolt gamma-rays from classical novae have hinted that shocks internal to the nova ejecta may dominate the nova emission. Shocks have also been suggested to power the luminosity of events as diverse as stellar mergers(3), supernovae(4) and tidal disruption events(5), but observational confirmation has been lacking. Here we report simultaneous space-based optical and gamma-ray observations of the 2018 nova V906 Carinae (ASASSN-18fv), revealing a remarkable series of distinct correlated flares in both bands. The optical and gamma-ray flares occur simultaneously, implying a common origin in shocks. During the flares, the nova luminosity doubles, implying that the bulk of the luminosity is shock powered. Furthermore, we detect concurrent but weak X-ray emission from deeply embedded shocks, confirming that the shock power does not appear in the X-ray band and supporting its emergence at longer wavelengths. Our data, spanning the spectrum from radio to gamma-ray, provide direct evidence that shocks can power substantial luminosity in classical novae and other optical transients. Simultaneous optical and gamma-ray observations of nova V906 Carinae reveal correlated flares in both wavelength ranges that can be linked to shocks in the nova ejecta. Weak X-ray emission suggests that the shocks are deeply embedded, but they contribute substantially to the luminosity of the nova.