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Issue A&A Volume 432, Number 2, March III 2005 Page(s) 401 - 410 Section Extragalactic astronomy DOI 10.1051/0004-6361:20041404

A&A 432, 401-410 (2005)
DOI: 10.1051/0004-6361:20041404

Structured jets in TeV BL Lac objects and radiogalaxies

Implications for the observed properties

G. Ghisellini¹, F. Tavecchio¹ and M. Chiaberge<sup>2

1</sup>  INAF - Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate, Italy
    e-mail: gabriele@merate.mi.astro.it
²  IRA/CNR, via Gobetti 101, 40129, Bologna, Italy

(Received 3 June 2004 / Accepted 28 October 2004 )

Abstract
TeV BL Lacertae objects require extreme relativistic bulk motions in the gamma-ray emission region, but at the VLBI scale their radio knots hardly move. The same sources show evidence, in radio, of a structure made of a fast spine plus a slow layer. We propose that this structure exists even on the spatial scale of regions responsible for the gamma-ray emission. One component sees the (beamed) radiation produced by the other, and this enhances the inverse Compton emission of both components. In addition, this allows the magnetic field to be nearly in equipartition with the emitting particles. The inverse Compton emission of the spine is anisotropic in its frame, possibly producing a deceleration of the spine by the Compton rocket effect. In this scenario, the slow layer is also a relatively strong high-energy emitter, and thus radiogalaxies become potentially detectable by GLAST.

Key words: galaxies: jets -- galaxies: BL Lacertae objects: general -- radio continuum: galaxies -- radiation mechanisms: non-thermal -- gamma-rays: theory

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© ESO 2005

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