Can Charge Exchange Explain Anomalous Soft X-ray Emission in the Cygnus Loop?

TL;DR

This study investigates whether charge exchange processes can explain the unexpected soft X-ray emission observed in the Cygnus Loop, finding that including charge exchange improves the model fit.

Contribution

The paper introduces a combined shock and charge exchange model to better explain X-ray emissions in the Cygnus Loop, highlighting the significance of charge exchange effects.

Findings

Charge exchange improves model fit to X-ray data.

A strong emission feature at 0.7 keV remains unexplained.

Charge exchange involving O7+ enhances the model significantly.

Abstract

Recent X-ray studies have shown that supernova shock models are unable to satisfactorily explain X-ray emission in the rim of the Cygnus Loop. In an attempt to account for this anomalously enhanced X-ray flux, we fit the region with a model including theoretical charge exchange (CX) data along with shock and background X-ray models. The model includes the CX collisions of $O^{8+}$, $O{7+}$, $N^{7+}$, $N^{6+}$, $C^{6+}$, and $C^{5+}$ with H with an energy of 1 keV/u (438 km/s). The observations reveal a strong emission feature near 0.7 keV that cannot fully be accounted for by a shock model, nor the current CX data. Inclusion of CX, specifically $O^{7+} + H$, does provide for a statistically significant improvement over a pure shock model.