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.

We studied all blazars of known redshift detected by the Fermi satellite during its first three months survey. For the majority of them, pointed Swift observations ensures a good multiwavelength coverage, enabling us to to reliably construct their spectral energy distributions (SED). We model the SEDs using a one-zone leptonic model and study the distributions of the derived interesting physical parameters as a function of the observed gamma-ray luminosity. We confirm previous findings concerning the relation of the physical parameters with source luminosity which are at the origin of the blazar sequence. The SEDs allow to estimate the luminosity of the accretion disk for the majority of broad emitting line blazars, while for the line-less BL Lac objects in the sample upper limits can be derived. We find a positive correlation between the jet power and the luminosity of the accretion disk in broad line blazars. In these objects we argue that the jet must be proton-dominated, and that the total jet power is of the same order of (or slightly larger than) the disk luminosity. We discuss two alternative scenarios to explain this result.Comment: 23 pages, 20 figures, accepted for publication in MNRAS. Very minosr change

We consider the constraints on the physical parameters of a homogeneous SSC model that can be derived from the spectral shape and variability of TeV blazars. Assuming that the relativistic electron spectrum is a broken power law, where the break energy $\gamma_b$ is a free parameter, we write the analytical formulae that allow to connect the physical parameters of the model to observable quantities. The constraints can be summarized in a plane where the coordinates are the Doppler factor and the magnetic field. The consistency between the break energy and the balance between cooling and escape and the interpretation of the soft photon lags measured in some sources as radiative cooling times are treated as additional independent constraints. We apply themethod to the case of three well known blazars, PKS 2155-304, Mrk 421 and Mrk 501.Comment: 36 pages, incl. 6 figures in PS format, AAS LaTeX, to be published in ApJ, Dec 199

Theoretical models for the production of relativistic jets from active galactic nuclei predict that jet power arises from the spin and mass of the central black hole, as well as the magnetic field near the event horizon 1 . The physical mechanism mechanism underlying the contribution from the magnetic field is the torque exerted on the rotating black hole by the field amplified by the accreting material. If the squared magnetic field is proportional to the accretion rate, then there will be a correlation between jet power and accretion luminosity. There is evidence for such a correlation 2-8 , but inadequate knowledge of the accretion luminosity of the limited and inhomogeneous used samples prevented a firm conclusion. Here we report an analysis of archival observations of a sample of blazars (quasars whose jets point towards Earth) that overcomes previous limitations. We find a clear correlation between jet power as measured through the γ-ray luminosity, and accretion luminosity as measured by the broad emission lines, with the jet power dominating over the disk luminosity, in agreement with numerical simulations 9 . This implies that the magnetic field threading the black hole horizon reaches the maximum value sustainable by the accreting matter 10 .The jet power is predicted 1 to depend on (aMB) 2 , where a and M are respectively the spin and mass of the black hole and B is the magnetic field at its horizon. Seed magnetic fields are amplified by the accretion disk up to equipartition with the mass energy density ∼ ρc 2 of the matter accreting at the rateṀ . A greaterṀ implies a larger ρ, that can sustain a larger magnetic field, which in turn can tap a larger amount of the black hole rotational energy. The magnetic field is thus a catalyst for the process. Increasing the spin of the black hole shrinks the innermost stable orbit, increasing the accretion efficiency η (defined by η = L disk /Ṁc 2 ) (L disk accretion disk luminosity) to a maximum value 11 η = 0.3.We use a well designed sample of blazars that have been detected in the γ-ray band by the Fermi Large Area Telescope (LAT) that have been spectroscopically observed in the optical 12, 13 (see Methods). They have been classified as BL Lac objects or Flat Spectrum Radio Quasars (FSRQs) according if the rest frame equivalent width of their broad emission lines was greater (FSRQ) or smaller (BL Lacs) than 5Å (rest frame). The sample contains 229 FSRQs, and 475 BL Lacs. Of the latter, 209 have a spectroscopically measured redshift. We considered all FSRQs with enough multi-wavelength data to have a Spectral Energy Distribution (SED) that allows to establish the bolometric luminosity. The considered FSRQs amount to 191 objects. Instead, for BL Lacs, we consider only the 26 sources with detected broad emission lines. This makes them the low disk luminosity tail of of the full 1 blazar sample. This choice is dictated by our will to measure the accretion luminosity, together with the jet power. Through the visible broad emission lines we reconstruct, through a t...