Volume 462, Number 1, January IV 2007
|Page(s)||29 - 41|
|Published online||02 November 2006|
Unveiling the X-ray/TeV engine in Mkn 421
Laboratoire Leprince-Ringuet, UMR 7638 CNRS, École Polytechnique, 91128 Palaiseau, France e-mail: firstname.lastname@example.org
2 Institut d'Astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie, Paris 6, 98 bis Bd. Arago, 75014 Paris, France
Accepted: 18 September 2006
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 . The full spectral energy distribution is well-fitted by synchrotron self-Compton emission from cooling electrons injected with a Maxwellian distribution of characteristic energy . Fluctuations in the injected power with 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.
Key words: acceleration of particles / radiation mechanisms: non-thermal / galaxies: active / BL Lacertae objects: individual: Mkn 421 / gamma rays: observations / X-rays: galaxies
© ESO, 2007
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