Blazar Times - No. 64 - September 2004
The Blazar Times
A Research Newsletter Dedicated to the BL Lac and Blazar Phenomena
No. 64 - September 2004 Editor: Travis A. Rector (


Journal Abstracts 1
Abstract Guidelines 3

Journal Abstracts
Are the jets accelerated from the disk coronas in some
active galactic nuclei?
Xinwu Cao
Shanghai Astronomical Observatory, Chinese Academy of
Sciences, 80 Nandan Road, Shanghai, 200030, China
We use a sample of radio-loud active galactic nuclei (AGNs) with estimated central black hole masses to explore their jet formation mechanisms. The jet power of AGNs is estimated from their extended radio luminosity. It is found that the jets in several AGNs of this sample are too powerful to be extracted from the standard thin accretion disks or rapidly spinning black holes surrounded by standard thin disks. If the advection dominated accretion flows (ADAFs) are present in these AGNs, their bright optical continuum luminosity cannot be produced by pure-ADAFs due to their low accretion rates and low radiation efficiency, unless the ADAFs transit to standard thin disks at some radii Rtr. If this is the case, we find that the dimensionless accretion rates [m\dot]=[M\dot]/[M\dot]Edd as high as 0.05 and transition from ADAFs to standard thin disks at rather small radii around ~ 20GMbh/c2 are required to explain their bright optical continuum emission. We propose that the disk-corona structure is present at least in some AGNs in this sample. The plasmas in the corona are very hot, and the pressure scale-height of the corona Hc ~ R. Powerful jets with Qjet ~ Lbol (bolometric luminosity) can form by the large-scale magnetic fields created by dynamo processes in the disk corona of some AGNs. The maximal jet power extractable from the corona Qjetmax 0.6Lc (Lc is the corona luminosity) is expected by this jet formation scenario. The statistic results on the sample of AGNs are consistent with the predictions of this scenario. Finally, the possibility that the jet is driven from a super-Keplerian rotating hot layer located between the corona and the cold disk is discussed. We find that, in principle, this layer can also produce a powerful jet with Qjet ~ Lbol.
Accepted by ApJ
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TV blazar gamma-ray emission produced by a cooling pile-up particle energy distribution function
Ludovic Saugé1 and Gilles Henri1
1 Laboratoire d'Astrophysique de Grenoble, Université Joseph-Fourier, BP 53, F-38041 Grenoble, France
We propose a time-dependent one-zone model based on a quasi-Maxwellian `pile-up' 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 (SSC) of ultra-relativistic leptons. The particle energy distribution function (EDF) is computed in a self-consistent way, taking into account an injection term of fresh particles, a possible pair creation term, and the particles radiative cooling. The source term is not a usual power-law but rather a `pile-up' distribution, which can result from the combination of a stochastic heating via second order Fermi process 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 (DIrB) and intrinsic absorption via the pair creation process. The model can reproduce very satisfactorily the observed spectral energy distribution (SED). 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 due to the sudden increase of soft photons density below the Klein-Nishina threshold. The possible relevance of such a scenario is discussed.
Accepted by ApJ
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Abstract Guidelines
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On 1 Aug 2004, 17:09.