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We report on two XMM-Newton observations of the planetary host star HD189733.The system has a close in planet and it can potentially affect the coronalstructure via interactions with the magnetosphere. We have obtained X-rayspectra and light curves from EPIC and RGS on board XMM-Newton which we haveanalyzed and interpreted. We reduced X-ray data from primary transit andsecondary eclipse occurred in April 17th 2007 and May 18th 2009, respectively.In the April 2007 observation only variability due to weak flares isrecognized. In 2009 HD189733 exhibited a X-ray flux always larger than in the2007 observation. The average flux in 2009 was higher than in 2007 observationby a factor of 45%. During the 2009 secondary eclipse we observed a softeningof the X-ray spectrum significant at level of ~3 sigma. Further, we observedthe most intense flare recorded at either epochs. This flare occurred 3 ksafter the end of the eclipse.The flare decay shows several minor ignitionsperhaps linked to the main event and hinting for secondary loops that emittriggered by the main loop. Magneto-Hydro-Dynamical (MHD) simulations show thatthe magnetic interaction between planet and star enhances the density and themagnetic field in a region comprised between the planet and the star because oftheir relative orbital/rotation motion. X-ray observations and modelpredictions are globally found in agreement, despite the quite simple MHD modeland the lack of precise estimate of parameters including the alignment and theintensity of stellar and planetary magnetic fields. Future observations shouldconfirm or disprove this hypothesis, by determining whether flares aresystematically recurring in the light curve at the same planetary phase.

XMM-Newton observations of HD189733 during planetary transits