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The mixed-morphology class of supernova remnants (MMSNRs) comprises a substantial fraction of observed remnants, but there is no consensus on their origin as yet. A clue to their nature is the presence of regions that show X-ray evidence of recombining plasmas. Recent calculations of remnant evolution in a cloudy interstellar medium that included thermal conduction but not nonequilibrium ionization (NEI) showed promise in explaining observed surface brightness distributions but could not determine whether recombining plasmas were present. In this paper, we present numerical hydrodynamic models of MMSNRs in 2D and 3D, including explicit calculation of NEI effects. Both the spatial ionization distribution and temperature–density diagrams show that recombination occurs inside the simulated MMSNR and that both adiabatic expansion and thermal conduction cause recombination, albeit in different regions. Features created by the adiabatic expansion stand out in the spatial and temperature–density diagrams, but thermal conduction also plays a role. Thus, thermal conduction and adiabatic expansion both contribute significantly to the cooling of high-temperature gas. Realistic observational data are simulated with both spatial and spectral input from various regions. We also discuss the possibility of analyzing the sources of recombination and dominant hydrodynamic processes in observations using temperature–density diagrams and spatial maps. [ABSTRACT FROM AUTHOR]

We report our independent GeV γ-ray study of the young shell-type supernova remnant (SNR) Kes 73, which harbors a central magnetar, and CO-line millimeter observations toward the SNR. Using 7.6 years of Fermi-LAT observation data, we detected an extended γ-ray source (“source A”) with centroid on the west of the SNR, with a significance of 21σ in 0.1–300 GeV and an error circle of 5.′4 in angular radius. The γ-ray spectrum cannot be reproduced by a pure leptonic emission or a pure emission from the magnetar, and thus a hadronic emission component is needed. The CO-line observations reveal a molecular cloud (MC) at VLSR ∼ 90 km s−1, which demonstrates morphological correspondence with the western boundary of the SNR brightened in multiwavelength. The 12CO (J = 2 − 1)/12CO (J = 1 − 0) ratio in the left (blue) wing 85–88 km s−1 is prominently elevated to ∼1.1 along the northwestern boundary, providing kinematic evidence of the SNR-MC interaction. This SNR-MC association yields a kinematic distance 9 kpc to Kes 73. The MC is shown to be capable of accounting for the hadronic γ-ray emission component. The γ-ray spectrum can be interpreted with a pure hadronic emission or a magnetar+hadronic hybrid emission. In the case of pure hadronic emission, the spectral index of the protons is 2.4, very similar to that of the radio-emitting electrons, essentially consistent with the diffusive shock acceleration theory. In the case of magnetar+hadronic hybrid emission, a magnetic field decay rate ≳1036 erg s−1 is needed to power the magnetar’s curvature radiation. [ABSTRACT FROM AUTHOR]