A systematic comparison of ionization temperatures between ionizing and recombining plasmas in supernova remnants

TL;DR

This paper compares ionization and electron temperatures in supernova remnants, revealing different plasma states and proposing a new evolutionary scenario for ionizing and recombining SNRs based on Suzaku observations.

Contribution

It introduces a new scenario explaining the temperature evolution and morphology differences between ionizing and recombining supernova remnants.

Findings

Recombining plasmas have higher ionization temperatures than electron temperatures.

Observed temperature profiles support the proposed evolutionary scenario.

Suzaku data provides new insights into plasma state transitions in SNRs.

Abstract

The temperatures of the plasma in the supernova remnants (SNRs) are initially very low just after the shock heating. The electron temperature (kT_{e}) increases quickly by Coulomb interaction, and then the energetic electrons gradually ionize atoms to increase the ionization temperature (kT_{i}). The observational fact is that most of the young and middle-to-old aged SNRs have lower kT_{i} than kT_{e} after the shock heating. The temperature evolution in the shell-like SNRs has been explained by this ionizing plasma (IP) scenario. On the other hand, in the last decade, a significant fraction of the mixed morphology SNRs was found to exhibit a recombining plasma (RP) with higher kT_{i} than kT_{e}. The origin and the evolution mechanism of the RP SNRs have been puzzling. To address this puzzle, this paper presents the kT_{e} and kT_{i} profiles using the observed results by follow-up Suzaku observations, and then proposes a new scenario for the temperature and morphology evolutions in the IP and RP SNRs.