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Astronomy and astrophysics (Berlin), 2007-01, Vol.462 (1), p.29-41
Ort / Verlag
Les Ulis: EDP Sciences
Erscheinungsjahr
2007
Link zum Volltext
Quelle
Free E-Journal (出版社公開部分のみ）
Beschreibungen/Notizen
Aims.Our goal was to find important clues concerning particle acceleration in relativistic jets through the analysis of multi-wavelength observations of TeV blazars. Methods.Simultaneous observations of Mkn 421 were taken in very high energy γ-rays (>200 GeV, CAT experiment), X-rays (RXTE), and optical (KVA). Multi-day RXTE observations are also presented, allowing for detailed modelling of the spectral variability. Results.Short timescale (≈30 mn) variations in VHE γ-rays are found, correlated with X-rays, but not with the optical. The X-ray spectrum hardens with flux until the photon indices saturate above a threshold flux ≈10-9erg s-1 cm-2. The fractional variability decreases from X-rays to optical as a power law with $F_{\rm var}\propto E^{0.24\pm0.01}$. The full spectral energy distribution is well-fitted by synchrotron self-Compton emission from cooling electrons injected with a Maxwellian distribution of characteristic energy $\gamma_b$. Fluctuations in the injected power with $P_{\rm inj}\propto \gamma_b^4$ explain the observed variability. Conclusions.The spectral saturation and the power-law dependence of the fractional variability are novel results that may extend to other TeV blazars. The ability of Maxwellian injections to reproduce the observed features suggest second-order Fermi acceleration or magnetic reconnection may play the dominant role in particle acceleration.