Wide band X-ray and optical observations of the BL Lac object 1ES 1959+650 in high state
Tagliaferri, G. ; Ravasio, M. ; Ghisellini, G. ; ...Giommi, P. ; et al.
Dec - 2003
DOI: 10.1051/0004-6361:20034051
ISSN : 0004-6361 ;
journal : Astronomy and Astrophysics

Issue : 3
type: Article Journal

Abstract
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, \R\_\\backslash rm C\\ 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.

keywords : P. Giommi: ASI author,X-rays: galaxies,galaxies: BL Lacertae objects: general,galaxies: BL Lacertae objects: individual: 1ES 195