Probing the Transition Between the Synchrotron and Inverse-compton Spectral Components of 1ES 1959+650
Abstract
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2010
- DOI:
- 10.1088/2041-8205/719/2/L162
- arXiv:
- arXiv:1010.3259
- Bibcode:
- 2010ApJ...719L.162B
- Keywords:
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- BL Lacertae objects: individual: 1ES 1959+650;
- galaxies: jets;
- radiation mechanisms: non-thermal;
- X-rays: galaxies;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 5 pages, 2 postscript figures