Another Abundance Inhomogeneity in the South East Limb of the Cygnus Loop

TL;DR

This study uses Suzaku observations to reveal significant metal abundance inhomogeneity along the Cygnus Loop's SE limb, with variations from half to 0.2 times solar, indicating complex plasma conditions and challenging previous assumptions.

Contribution

It provides the first detailed spatially-resolved spectroscopic analysis of the Cygnus Loop's SE limb, highlighting abundance inhomogeneity and its independence from radio emission features.

Findings

Abundance at the limb edge is about half solar.

Inner regions show about 0.2 times solar abundance.

Abundance inhomogeneity is similar to the NE limb, indicating widespread complexity.

Abstract

We have observed the south-east (SE) limb of the Cygnus Loop with {\it Suzaku}. Our spatially-resolved spectroscopic study shows that a one-$kT_\mathrm{e}$ non-equilibrium ionization model represents our spectra fairly well. We find that the metal abundances obtained are all depleted relative to the solar values with a positional dependency along the radial direction of the Cygnus Loop. The abundances in the very edge of the limb shows about half the solar value, whereas other regions inside the Loop show about 0.2 times the solar value which has been believed as a typical value for the Cygnus Loop limb. The "enhanced" abundance in the very edge in the SE limb is quite similar to that found in the north-east (NE) limb of the Loop, and thus this is another evidence of abundance inhomogeneity in the limb regions of the Loop. The radio map shows a quite different feature: the NE limb is in the radio bright region while the SE limb shows almost no radio. Therefore, the metal abundance variation in the SE limb can not attribute to the non-thermal emission. The abundance inhomogeneity as well as the metal depletion down to 0.2 times the solar value still remain an open question.