Confronting the Superbubble Model with X-Ray Observations of 30 Doradus C

We present an analysis of XMM-Newton observations of the superbubble 30 Dor C and compare the results with the predictions from the standard wind-blown bubble model. We find that the observed X-ray spectra cannot be fitted satisfactorily with the model alone and that there is evidence for nonthermal X-ray emission, which is particularly important at ≳4 keV. The combination of the bubble model and a power law gives a reasonable fit to the observed spectra. The thermal pressure and central temperature of the bubble are 3.3 × 10^-11 dynes cm^-2 and 7.4 × 10⁶ K, respectively, and we infer that for a bubble age of t ~ 4 × 10⁶ yr the ambient density is n₀ ≃ 38 cm^-3, the mechanical luminosity is L_mech ~ 10³⁷ ergs s^-1, and the coefficient of thermal conductivity is ~0.05 of the Spitzer value. The total unabsorbed 0.1-10 keV luminosities of the eastern and western parts of the bubble are ≃3 × 10³⁶ and ≃5 × 10³⁶ ergs s^-1, respectively. The unabsorbed 0.1-10 keV luminosity of the bubble model is ~4 × 10³⁶ ergs s^-1, and so the power-law component contributes between and of the total unabsorbed luminosity in this energy band. The nature of the hard nonthermal emission is not clear, although recent supernovae in the bubble may be responsible. We expect that about one or two core-collapse supernovae could have occurred and are required to explain the enrichment of the hot gas, as evidenced by the overabundance of α-elements by a factor of ≳3, compared to the mean value of ~0.5 solar for the interstellar medium in the Large Magellanic Cloud. As in previous studies of various superbubbles, the amount of energy currently present in 30 Dor C is significantly less than the expected energy input from the enclosed massive stars over their lifetime. We speculate that a substantial fraction of the input energy may be radiated in the far-infrared by dust grains, which are mixed with the hot gas because of the thermal conduction and/or dynamic mixing.