Probing the Transition Between the Synchrotron and Inverse-compton Spectral Components of 1ES 1959+650

E. Bottacini, M. Böttcher, P. Schady, A. Rau, X. -L. Zhang, M. Ajello, C. Fendt, J. Greiner

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12 Citations (SciVal)


1ES 1959+650 is one of the most remarkable high-peaked BL Lacertae objects (HBL). In 2002, it exhibited a TeV γ-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, the Swift X-Ray Telescope, and the UV-Optical Telescope, and nearly simultaneously with a ground-based optical telescope. The steep spectral component at X-ray energies is most likely due to synchrotron emission, while at soft γ-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 γ-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 ~ 1.85, possibly indicating the relevance of second-order Fermi acceleration.
Original languageEnglish
Pages (from-to)L162-L166
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 20 Aug 2010


  • BL Lacertae objects: individual: 1ES 1959+650, galaxies: jets, radiation mechanisms: non-thermal, X-rays: galaxies, Astrophysics - High Energy Astrophysical Phenomena


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