1ES 1959+650 is one of the most remarkable high-peaked BL Lacertae objects ( HBL ) .
In 2002 it exhibited a TeV \gamma –ray flare without a similar brightening of the synchrotron component at lower energies .
This orphan TeV flare remained a mystery .
We present the results of a multifrequency campaign , triggered by the INTEGRAL IBIS detection of 1ES 1959+650 .
Our data range from the optical to hard X-ray energies , thus covering the synchrotron and inverse-Compton components simultaneously .
We observed the source with INTEGRAL , Swift /XRT , and UV-Optical Telescope , and nearly simultaneously with ground-based optical telescope .
The steep spectral component at X-ray energies is most likely due to synchrotron emission , while at soft \gamma -ray energies the hard spectral index may be interpreted as the onset of the high-energy component of the blazar spectral energy distribution ( SED ) .
This is the first clear measurement of a concave X-ray – soft \gamma -ray spectrum for an HBL .
The SED can be well modeled with a leptonic synchrotron- self-Compton model .
When the SED is fitted this model requires a very hard electron spectral index of q \sim 1.85 , possibly indicating the relevance of second-order Fermi acceleration .