Observations of the post-shock break-out emission of SN 2011dh with XMM-Newton

Context. After the occurrence of the type cIIb SN 2011dh in the nearby spiral galaxy M 51 numerous observations were performed with different telescopes in various bands ranging from radio to gamma-rays. Aims. We analysed the XMM-Newton and Swift observations taken 3 to 30 days after the SN explosion to study the X-ray spectrum of SN 2011dh. Methods. We extracted spectra from the XMM-Newton observations, which took place similar to 7 and 11 days after the SN. In addition, we created integrated Swift/XRT spectra of 3 to 10 days and 11 to 30 days. Results. The spectra can be well-fitted with a power-law spectrum absorbed with Galactic foreground absorption. In addition, we find a harder spectral component in the first XMM-Newton spectrum taken at t approximate to 7 d. This component is also detected in the first Swift spectrum of t = 3-10 d. Conclusions. While the persistent component can be explained as inverse Compton emission from radio synchrotron emitting electrons or emission of the reverse shock, the harder component is most likely bremsstrahlung emission from the shocked stellar wind. Therefore, the harder X-ray emission that fades away after t approximate to 10 d can be interpreted as emission from the shocked circumstellar wind of SN 2011dh.