Three-dimensional modeling of the asymmetric blast wave from the 2006 outburst of RS Ophiuchi: Early X-ray emission

TL;DR

This study combines 3-D hydrodynamic simulations with Chandra X-ray observations to reveal the asymmetric structure and origin of early X-ray emission in the 2006 outburst of RS Ophiuchi, highlighting the role of equatorial density enhancements.

Contribution

The paper introduces a detailed 3-D hydrodynamic model that reproduces observed X-ray line asymmetries and profiles, providing new insights into the blast wave-CSM interaction in recurrent novae.

Findings

Model reproduces observed asymmetric, blue-shifted X-ray lines.

X-ray emission mainly from a small region behind the interaction front.

Asymmetries caused by absorption of red-shifted emission by ejecta.

Abstract

Chandra/HETG observations of the recurrent nova RS Ophiuchi at day 13.9 of its 2006 outburst reveal a spectrum covering a large range in plasma temperature and characterized by asymmetric and blue-shifted emission lines. We investigate the origin of these asymmetries and broadening of emission lines. We perform 3-D hydrodynamic simulations of the blast wave from the 2006 outburst, propagating through the inhomogeneous CSM. The model takes into account the thermal conduction (including the effects of heat flux saturation) and the radiative cooling. From the simulations, we synthesize the X-ray emission and derive the spectra as they would be observed with Chandra/HETG. Our model reproduces the observed X-ray emission in a natural way if the CSM in which the outburst occurred is characterized by an equatorial density enhancement. Our ``best-fit'' model predicts that most of the early X-ray emission originates from a small region propagating in the direction perpendicular to the line-of-sight and localized just behind the interaction front between the blast wave and the equatorial density enhancement. The model predicts asymmetric and blue-shifted line profiles remarkably similar to those observed. These asymmetries are due to substantial X-ray absorption of red-shifted emission by ejecta material. The comparison of high quality data of Chandra/HETG with detailed hydrodynamic modeling has allowed us to unveil, for the first time, the details of the structure emitting in the X-ray band in early phases of the outburst evolution, contributing to a better understanding of the physics of interactions between nova blasts and CSM in recurrent novae. This may have implications for whether or not RS Ophiuchi is a Type Ia SN progenitor system.