# Localized Recombining Plasma in G166.0+4.3: A Supernova Remnant with an Unusual Morphology

## TL;DR

This study analyzes Suzaku X-ray observations of supernova remnant G166.0+4.3, revealing localized recombining plasma likely formed by thermal conduction with nearby cool dense gas, supported by multi-wavelength data.

## Contribution

First detailed X-ray spectral analysis of G166.0+4.3 revealing localized recombining plasma and its possible formation mechanism via thermal conduction.

## Key findings

- Recombining plasma detected only in the northeastern region.
- The plasma has an electron temperature of about 0.46 keV.
- Evidence suggests interaction with a molecular cloud.

## Abstract

We observed the Galactic mixed-morphology supernova remnant G166.0+4.3 with Suzaku. The X-ray spectrum in the western part of the remnant is well represented by a one-component ionizing plasma model. The spectrum in the northeastern region can be explained by two components. One is the Fe-rich component with the electron temperature $kT_e = 0.87_{-0.03}^{+0.02}$ keV. The other is the recombining plasma component of lighter elements with $kT_e = 0.46\pm0.03$ keV, the initial temperature $kT_{init} = 3$ keV (fixed) and the ionization parameter $n_et = (6.1_{-0.4}^{+0.5}) \times 10^{11} \rm cm^{-3} s$. As the formation process of the recombining plasma, two scenarios, the rarefaction and thermal conduction, are considered. The former would not be favored since we found the recombining plasma only in the northeastern region whereas the latter would explain the origin of the RP. In the latter scenario, an RP is anticipated in a part of the remnant where blast waves are in contact with cool dense gas. The emission measure suggests higher ambient gas density in the northeastern region. The morphology of the radio shell and a GeV gamma-ray emission also suggest a molecular cloud in the region.