X-ray emission from an asymmetric blast wave and a massive white dwarf in the gamma-ray emitting nova V407 Cyg

Classical nova events in symbiotic stars, although rare, offer a unique opportunity to probe the interaction between ejecta and a dense environment in stellar explosions. In this work, we use X-ray data obtained with Swift and Suzaku during the recent classical nova outburst in V407 Cyg to explore such an interaction. We find evidence of both equilibrium and non-equilibrium ionization plasmas at the time of peak X-ray brightness, indicating a strong asymmetry in the density of the emitting region. Comparing a simple model to the data, we find that the X-ray evolution is broadly consistent with nova ejecta driving a forward shock into the dense wind of the Mira companion. We detect a highly absorbed soft X-ray component in the spectrum during the first 50days of the outburst that is consistent with supersoft emission from the nuclear burning white dwarf. The high temperature and short turnoff time of this emission component, in addition to the observed breaks in the optical and UV light curves, indicate that the white dwarf in the binary is extremely massive. Finally, we explore the connections between the X-ray and GeV γ-ray evolution, and propose that the gamma-ray turnoff is due to the stalling of the forward shock as the ejecta reach the red giant surface.