Toward the Understanding of the Physical Origin of Recombining Plasma in the Supernova Remnant IC 443

TL;DR

This study conducts a detailed spatially resolved X-ray spectroscopic analysis of supernova remnant IC 443, revealing the widespread presence of recombining plasma components and their cooling mechanisms, especially near molecular clouds.

Contribution

First to report recombining plasma in multiple regions of IC 443, elucidating their temperature distribution and cooling processes through Suzaku observations.

Findings

Recombining plasma components are present throughout IC 443.

Electron temperatures decrease toward the southeast, indicating cooling.

Thermal conduction with molecular clouds likely causes plasma cooling.

Abstract

We perform a spatially resolved spectroscopic analysis of X-ray emission from the supernova remnant (SNR) IC 443 with Suzaku. All the spectra are well reproduced by a model consisting of a collisional ionization equilibrium (CIE) and two recombining plasma (RP) components. Although previous X-ray studies found an RP in the northeastern region, this is the first report on RPs in the other parts of the remnant. The electron temperature $kT_e$ of the CIE component is almost uniform at $\sim 0.2$ keV across the remnant. The CIE plasma has metal abundances consistent with solar and is concentrated toward the rim of the remnant, suggesting that it is of shocked interstellar medium origin. The two RP components have different $kT_e$: one in the range of 0.16$-$0.28 keV and the other in the range of 0.48$-$0.67 keV. The electron temperatures of both RP components decrease toward the southeast, where the SNR shock is known to be interacting with a molecular cloud. We also find the normalization ratio of the lower-$kT_e$ RP to higher-$kT_e$ RP components increases toward the southeast. Both results suggest the X-ray emitting plasma in the southeastern region is significantly cooled by some mechanism. One of the plausible cooling mechanisms is thermal conduction between the hot plasma and the molecular cloud. If the cooling proceeds faster than the recombination timescale of the plasma, the same mechanism can account for the recombining plasma as well.