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The hard TeV spectrum of 1ES 0229+200: new clues from Swift




The BL Lac object 1ES 0229+200 (z= 0.14) has been detected by the High Energy Stereoscopic System (HESS) during observations taking place in 2005–2006. The TeV spectrum, when corrected for the absorption of gamma-ray photons through the interaction with the extragalactic background light, is extremely hard, even if the most conservative level for the background is considered. The case of 1ES 0229+200 is very similar to that of 1ES 1101−232, for which a possible explanation, in the framework of the standard one-zone synchrotron-self Compton (SSC) model, is that the high-energy emission is SSC radiation of electrons distributed as a power law with a large value of the minimum energy. In this scenario, the hard TeV spectrum is accompanied by a very hard synchrotron continuum below the soft X-ray band. We will show that recent Swift observations of 1ES 0229+200 in the critical UV X-ray band support this model, showing the presence of the expected spectral break and hard continuum between the UV and the X-ray bands.