Multi-wavelength Study of the Supernova Remnant Kes 79 (G33.6+0.1): On Its Supernova Properties and Expansion into a Molecular Environment

Abstract

Kes 79 (G33.6+0.1) is an aspherical thermal composite supernova remnant (SNR) observed across the electromagnetic spectrum and showing an unusual highly structured morphology, in addition to harboring a central compact object (CCO). Using the CO J = 1-0, J = 2-1, and J = 3-2 data, we provide the first direct evidence and new morphological evidence to support the physical interaction between the SNR and the molecular cloud in the local standard of rest velocity ∼ 105 {km} {{{s}}}^-1. We revisit the 380 ks XMM-Newton observations and perform a dedicated spatially resolved X-ray spectroscopic study with careful background subtraction. The overall X-ray-emitting gas is characterized by an under-ionized ({τ }_{{c}}∼ 6× {10}¹¹ {{cm}}^-3) cool ({{kT}}_{{c}}≈ 0.20 keV) plasma with solar abundances, plus an under-ionized ({τ }_{{h}}∼ 8× {10}¹⁰ {{cm}}^-3) hot ({{kT}}_{{h}}≈ 0.80 keV) plasma with elevated Ne, Mg, Si, S, and Ar abundances. The X-ray filaments, spatially correlated with the 24 μ {{m}} IR filaments, are suggested to be due to the SNR shock interaction with dense gas, while the halo forms from SNR breaking out into a tenuous medium. Kes 79 appears to have a double-hemisphere morphology viewed along the symmetric axis. Projection effect can explain the multiple-shell structures and the thermal composite morphology. The high-velocity, hot ({{kT}}_{{h}}∼ 1.4{--}1.6 keV) ejecta patch with high metal abundances, together with the non-uniform metal distribution across the SNR, indicate an asymmetric SN explosion of Kes 79. We refine the Sedov age to 4.4-6.7 kyr and the mean shock velocity to 730 {km} {{{s}}}^-1. Our multi-wavelength study suggests a progenitor mass of ∼15-20 solar masses for the core-collapse explosion that formed Kes 79 and its CCO, PSR J1852+0040.