The Plasma Structure of the Cygnus Loop from the Northeastern Rim to the Southwestern Rim

TL;DR

This study uses XMM-Newton observations to analyze the plasma structure of the Cygnus Loop, revealing a complex, asymmetric ejecta distribution and variations in the cavity wall, supporting a cavity explosion origin.

Contribution

It provides detailed spatially-resolved X-ray spectral analysis of the Cygnus Loop, identifying multiple plasma components and their distribution, and inferring explosion asymmetry and progenitor mass.

Findings

Low-kTe component surrounds high-kTe ejecta due to projection effects.

Ejecta metals show non-uniform, asymmetric distribution.

Evidence of a blowout in the cavity wall in the southwest region.

Abstract

The Cygnus Loop was observed from the northeast to the southwest with XMM-Newton. We divided the observed region into two parts, the north path and the south path, and studied the X-ray spectra along two paths. The spectra can be well fitted either by a one-component non-equilibrium ionization (NEI) model or by a two-component NEI model. The rim regions can be well fitted by a one-component model with relatively low \kTe whose metal abundances are sub-solar (0.1--0.2). The major part of the paths requires a two-component model. Due to projection effects, we concluded that the low kTe (about 0.2 keV) component surrounds the high kTe (about 0.6 keV) component, with the latter having relatively high metal abundances (about 5 times solar). Since the Cygnus Loop is thought to originate in a cavity explosion, the low-kTe component originates from the cavity wall while the high-kTe component originates from the ejecta. The flux of the cavity wall component shows a large variation along our path. We found it to be very thin in the south-west region, suggesting a blowout along our line of sight. The metal distribution inside the ejecta shows non-uniformity, depending on the element. O, Ne and Mg are relatively more abundant in the outer region while Si, S and Fe are concentrated in the inner region, with all metals showing strong asymmetry. This observational evidence implies an asymmetric explosion of the progenitor star. The abundance of the ejecta also indicates the progenitor star to be about 15 M_sun.