X-ray Emission from an Asymmetric Blast Wave and a Massive White Dwarf in the Gamma-ray Emitting Nova V407 Cyg

TL;DR

This study analyzes X-ray data from the 2010 nova V407 Cyg, revealing asymmetric shock interactions, a massive white dwarf, and connections between X-ray and gamma-ray emissions, enhancing understanding of nova explosions in symbiotic systems.

Contribution

It provides the first detailed X-ray analysis of V407 Cyg's nova outburst, highlighting asymmetries, the white dwarf's mass, and the shock dynamics linking X-ray and gamma-ray emissions.

Findings

Evidence of asymmetric plasma ionization states.

Detection of supersoft X-ray emission indicating a massive white dwarf.

Correlation between shock evolution and gamma-ray turn-off.

Abstract

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 50 days of the outburst that is consistent with supersoft emission from the nuclear burning white dwarf. The high temperature and short turn off time of this emission component, in addition to the observed breaks in the optical and UV lightcurves, indicate that the white dwarf in the binary is extremely massive. Finally, we explore the connections between the X-ray and GeV gamma-ray evolution, and propose that the gamma ray turn-off is due to the stalling of the forward shock as the ejecta reach the red giant surface.