Linking radio and gamma ray emission in Ap Librae

Ap Lib is one of the rare Low Synchrotron Peaked blazars detected so far at TeV energies. This type of source is not properly modelled by standard one-zone leptonic Synchrotron-self-Compton (SSC) emission scenarios. The aim of this paper is to study the relevance of additional components which should naturally occur in a SSC scenario for a better understanding of the emission mechanisms, especially at very high energies (VHE). Methods. We use simultaneous data from a multi-wavelength campaign of Planck, Swift-UVOT and Swift-XRT telescopes carried out in February 2010, as well as quasi-simultaneous data of WISE, Fermi and H.E.S.S. taken in 2010. The multi-lambda emission of Ap Lib is modelled by a blob-in-jet SSC scenario including the contribution of the base of the VLBI extended jet, the radiative blob-jet interaction, the accretion disk and its associated external photon field. We show that signatures of a strong parsec-scale jet and of an accretion disk emission are present in the SED. We can link the observationnal VLBI jet features from MOJAVE to parameters expected for a VHE emitting blob accelerated near the jet base. The VHE emission appears to be dominated by the inverse-Compton effect of the blob relativistic electrons interacting with the jet synchrotron radiation. In such scenario Ap Lib appears as an intermediate source between BL Lac objects and Flat Spectrum Radio Quasars. Ap Lib could be a bright representative of a specific class of blazars, in which the parsec-scale jet luminosity is no more negligible compared to the blob and contributes to the high energy emission via inverse Compton processes.Comment: 12 pages, 7 figures, Accepted for publication in A&

An innovative blazar classification based on radio jet kinematics

Blazars are usually classified following their synchrotron peak frequency ($\nu F(\nu)$ scale) as high, intermediate, low frequency peaked BL Lacs (HBLs, IBLs, LBLs), and flat spectrum radio quasars (FSRQs), or, according to their radio morphology at large scale, FR~I or FR~II. However, the diversity of blazars is such that these classes seem insufficient to chart the specific properties of each source. We propose to classify a wide sample of blazars following the kinematic features of their radio jets seen in very long baseline interferometry (VLBI). For this purpose we use public data from the MOJAVE collaboration in which we select a sample of blazars with known redshift and sufficient monitoring to constrain apparent velocities. We selected 161 blazars from a sample of 200 sources. We identify three distinct classes of VLBI jets depending on radio knot kinematics: class I with quasi-stationary knots, class II with knots in relativistic motion from the radio core, and class I/II, intermediate, showing quasi-stationary knots at the jet base and relativistic motions downstream. A notable result is the good overlap of this kinematic classification with the usual spectral classification; class I corresponds to HBLs, class II to FSRQs, and class I/II to IBLs/LBLs. We deepen this study by characterizing the physical parameters of jets from VLBI radio data. Hence we focus on the singular case of the class I/II by the study of the blazar BL Lac itself. Finally we show how the interpretation that radio knots are recollimation shocks is fully appropriate to describe the characteristics of these three classes.Comment: 12 pages, 13 figures, accepted by A&

The buried Balmer-edge signatures from quasars

In our previous paper, we have reported the detection of a Balmer edge absorption feature in the polarized flux of one quasar (Ton 202). We have now found similar Balmer edge features in the polarized flux of four more quasars (4C09.72, 3C95, B2 1208+32, 3C323.1), and possibly a few more, out of 14 newly observed with the VLT and Keck telescopes. In addition, we also re-observed Ton 202, but we did not detect such a dramatic feature, apparently due to polarization variability (the two observations are one-year apart). The polarization measurements of some quasars are affected by an interstellar polarization in our Galaxy, but the measurements have been corrected for this effect reasonably well. Since the broad emission lines are essentially unpolarized and the polarization is confined only to the continuum in the five quasars including Ton 202 in both epochs, the polarized flux is considered to originate interior to the broad emission line region. The Balmer edge feature seen in the polarized flux is most simply interpreted as an intrinsic spectral feature of the quasar UV/optical continuum, or the ``Big Blue Bump'' emission. In this case, the edge feature seen in absorption indeed indicates the thermal and optically-thick nature of the continuum emitted. However, we also discuss other possible interpretations.Comment: Accepted for publication in MNRAS; 31 pages, 38 figures with reduced resolutions; the paper with a full resolution is at http://www.roe.ac.uk/~mk/papers/04Ba_vk.ps.g

Hydrodynamics and Metzner-Otto correlation in stirred vessels for yield stress fluids

This paper investigates the hydrodynamics and power consumption in laminar stirred vessel flowusing numerical computation. The Metzner–Otto correlation was established for mixing in power-law fluids. This paper focuses on its application to yield stress fluids. Distributions of shear rates and their link to power consumption for helical and anchor agitators are discussed. Insight is sought from the analytical formula for Taylor–Couette flows. Laws are established for Bingham, Herschel-Bulkley and Casson fluids and reveal similar results. Fully or partially sheared flow situations with plug regions are considered. Depending on the fluid model, the concept is valid or constitutes a satisfactory approximation for fully sheared flows. When the flow is partially sheared, the expression depends on the Bingham number and the concept must be adapted. The results of the numerical simulations are interpreted in the light of this analysis and results from the literature

A mixed lepto-hadronic scenario for PKS 2155-304

The models developed to describe the spectral energy distribution (SED) of blazars can be divided into leptonic or hadronic scenarios, according to the particles responsible for the high-energy component. We have developed a new stationary code which computes all the relevant leptonic and hadronic processes, permitting the study of both leptonic and hadronic scenarios in a consistent way. Interestingly, mixed lepto-hadronic scenarios (in which both components contribute to the high energy emission) naturally arise in this framework. We present the first application to the well known BL Lac object PKS 2155-304.Comment: 4 pages, 1 figure; to appear in the proceedings of the Gamma 2012 conferenc

Le théâtre ou l’exhibition du monstre. La mise en scène des corps stigmatisés dans Giulio Cesare de Romeo Castellucci

Le spectacle Giulio Cesare de la Societas Raffaello Sanzio met en scène des acteurs aux corps stigmatisés, dont la vision déstabilise fortement les spectateurs. Mais le choc créé n’est pas gratuit. Intégré à l’ensemble de la représentation, il devient un moyen de jouer sur les structures profondes du théâtre. Si le stigmate souligne le corps de l’acteur de manière radicale, il permet également de transformer le statut de ce dernier. Ces corps stigmatisés viennent en fait redoubler et souligner un phénomène essentiel : la scène fait toujours de l’acteur un être exhibé et soumis aux regards, un être monstrueux, dont l’identité vacille avant d’être à nouveau symbolisée.In the play Giulio Cesare, by the Societas Raffaello Sanzio, the actors' stigmatised bodies strongly destabilized the audience. But the shock was not unmotivated. Being integrated into the performance as a whole, it becomes a mean to play on the underlying structures of theatre. The stigmata does not only emphasize the actor's body radically but it also transforms his status. These stigmatized bodies virtually enlight an essential phenomenon: on stage, the actor is always turned into an exhibited being, subject to the eye—a monstrous being, whom identity flickers until it is symbolized again