An XMM-Newton study of the mixed-morphology supernova remnant W28 (G6.4-0.1)

Abstract

We have performed an XMM-Newton imaging and spectroscopic study of supernova remnant (SNR) W28, a prototype mixed-morphology or thermal composite SNR, believed to be interacting with a molecular cloud. The observed hot X-ray emitting plasma is characterized by low metal abundances, showing no evidence of ejecta. The X-rays arising from the deformed northeast shell consist of a thermal component with a temperature of $\sim 0.3$ keV plus a hard component of either thermal (temperature $\sim 0.6$ keV) or non-thermal (photon index $=0.9$-2.4) origin. The X-ray emission in the SNR interior is blobby and the corresponding spectra are best described as the emission from a cold ($kT\sim 0.4$ keV) plasma in non-equilibrium ionization with an ionization timescale of $\sim 4.3\times 10^{11}$ cm${}^{-3}$ s plus a hot ($kT\sim 0.8$ keV) gas in collisional ionization equilibrium. Applying the two-temperature model to the smaller central regions, we find non-uniform interstellar absorption, temperature and density distribution, which indicates that the remnant is evolving in a non-uniform environment with denser material in the east and north. The cloudlet evaporation mechanism can essentially explain the properties of the X-ray emission in the center and thermal conduction may also play a role for length scales comparable to the remnant radius. A recombining plasma model with an electron temperature of $\sim 0.6$ keV is also feasible for describing the hot central gas with the recombination age of the gas estimated at $\sim 2.9\times 10^4$ yr.

arXiv comment16 pages, 7 figures, 5 tables, ApJ in press

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• CTIO, ROSAT HRI and Chandra ACIS Observations of the Archetypical Mixed-Morphology Supernova Remnant W28 (G6.4-0.1)
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• Spatially-Resolved Study of Recombining Plasma in W49B Using XMM-Newton
• Chandra observations of the HII complex G5.89-0.39 and TeV gamma-ray source HESSJ1800-240B
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