TeV Blazar Gamma-Ray Emission Produced by a Cooling Pileup Particle Energy Distribution Function

• Published in: The Astrophysical journal 2004-11, Vol.616 (1), p.136-146
• Main Authors: Saugé, Ludovic, Henri, Gilles
• Format: Article
• Language: English
• Subjects: Active and peculiar galaxies (including bl lacertae objects, blazars, seyfert galaxies, markarian galaxies, active galactic nuclei); Astronomy; Earth, ocean, space; Exact sciences and technology; Fundamental aspects of astrophysics; Fundamental astronomy and astrophysics. Instrumentation, techniques, and astronomical observations; Quasars. Active or peculiar galaxies, objects, and systems; Radiation mechanisms, polarization; Stellar systems. Galactic and extragalactic objects and systems. The universe
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/424905

We propose a time-dependent one-zone model based on a quasi-Maxwellian "pileup" distribution in order to explain the time-averaged high-energy emission of TeV blazars. The instantaneous spectra are the result of the synchrotron and synchrotron self-Compton emission of ultrarelativistic leptons. The particle energy distribution function is computed in a self-consistent way, taking into account an injection term of fresh particles, a possible pair creation term, and the radiative cooling of the particles. The source term is not a usual power law but rather a pileup distribution, which can result from the combination of stochastic heating via second-order Fermi processes and radiative cooling. To validate this approach, we have performed time-averaged fits of the well-known TeV emitter Mrk 501 during the 1997 flaring activity period, taking into account the attenuation of the high-energy component by cosmic diffuse infrared background and intrinsic absorption via the pair creation process. The model can reproduce very satisfactorily the observed spectral energy distribution. A high Lorentz factor is required to avoid strong pair production; in the case of smaller Lorentz factor, an intense flare in the GeV range is predicted because of the sudden increase of soft photon density below the Klein-Nishina threshold. The possible relevance of such a scenario is discussed.