Wide band X-ray and optical observations of the BL Lac object 1ES 1959+650 in high state

The blazar 1ES 1959+ 650 was observed twice by BeppoSAX in September 2001 simultaneously with optical observations. We report here the X- ray data together with the optical, RC magnitude light curve since August 1995. The BeppoSAX observations were triggered by an active X- ray status of the source. The X- ray spectra are brighter than the previously published X- ray observations, although the source was in an even higher state a few months later, as monitored by the ASM onboard RossiXTE, when it was also detected to flare in the TeV band. Our X- ray spectra are well represented by a continuosly curved model up to 45 keV and are interpreted as synchrotron emission, with the peak moving to higher energies. This is also confirmed by the slope of the X- ray spectrum which is harder than in previous observations. Based on our optical and X- ray data, the synchrotron peak turns out to be in the range 0.1 - 0.7 keV. We compare our data with non- simultaneous radio to TeV data and model the spectral energy distribution with a homogeneous, one- zone synchrotron inverse Compton model. We derive physical parameters that are typical of low power High Energy peaked Blazars, characterised by a relatively large beaming factor, low luminosity and absence of external seed photons.