Alphabetical List of People Presenting Work with Abstracts:

Juan Carlos Algaba
(poster)
Investigations of Correlations between the Radio and Optical Polarization of AGN.

Fathallah Alouani Bibi
Impact of supersonic AGN jet on non homogeneous intracluster medium
Abstract: We performed a series of three dimensional AMR hydrodynamic simulations of AGN jet interaction with cooling flow clusters. We analyzed the impact of heat flux and viscosity on the redistribution of jet energy throughout the intracluster medium. Preliminary estimates of the effect of magnetic field on transverse heat flux and viscosity coefficients are made. The limits of the applicability of the classical Spitzer theory for heat flux in the intracluster gas and the thermal inhibition within such environment due to the shape of the electron distribution function are discussed.

Jonathan Arons
Beam Filamentation Instability of Interacting Current Sheets in Striped Relativistic Winds: The Origin of Low Sigma?
Abstract: Several lines of evidence suggest that relativistic winds from pulsars have flow energy dominated by kinetic energy at their termination, even though they emerge from the light cylinder as Poynting flux dominated flows. The wind sources are oblique rotators, thus the winds are ``striped'' - composed of interleaved sectors of oppositely directed ${\boldsymbol B} $ in a wide sector of latitude around the rotational equator. The electric current in the sheets separating the oppositely directed magnetic fields of the stripes, which provide the star's electric return current, is composed of a high energy particle beam, propagating across the magnetic field in an almost unmagnetized channel of thickness comparable to the particles' formal Larmor radius. The beams in neighboring sheets have opposite propagation directions, and interact across the stripes through the long range electromagnetic field. Thus the beams are subject to an electromagnetic shear instability which has strong kinship to Weibel beam filamentation instabilities in unmagnetized plasmas.
I outline the physics of this instability, apply it to the pair dominated winds from pulsars, both in the case when the return current is composed of ions or high energy positrons (angle between the angular velocity and the magnetic moment less than 90 degrees, an "acute" pulsar) and also in the electron beam return current case (angle between the angular velocity and the magnetic moment greater than 90 degrees, an "obtuse" pulsar). I argue that the instability saturates through magnetic trapping, which leads to the appearance of an anomalous resistance in the pulsar circuit, and show that this resistance can account for the reduction of the striped component of the winds' magnetic fields, through broadening of the current layers until they merge and the stripes disappear. I discuss some possible observational consequences of this magnetic dissipation in the apparently dark region between the light cylinder and the winds' termination shocks.

Maxim Barkov
Magnetic acceleration of relativistic jets
Abstract: In this work we describe computer simulations of axisymmetric isentropic magnetically driven relativistic jets. The overall collimation of the jets, that is the shape of the jet boundary, is imposed via suitable boundary conditions and varies from conical to paraboloidal ($z \propto r^a$) with the collimation index $a=3$. The external pressure, that is needed for confining of the jets, is close to the power law, $p\propto z^{-s}$, with the power index varying from 1.1 to 3.5 and thus covering most of the astrophysically interesting conditions. At the inlet these jets are sub-Alfvenic and magnetically dominated with the ratio of the Poynting flux to the total particle energy flux reaching $\simeq 15$. All the jets show effective acceleration and conversion of the Poynting flux into the kinetic energy of the flow. The ratio of the particle energy to the electromagnetic energy becomes as high as 4 in the most distant parts of the jets and continues to grow. At the same time the Lorentz factor approaches its highest theoretically possible value, up to $\Gamma=15$ in these simulations. The rate of conversion is higher for flows with lower collimation index so that the most effective acceleration is reached by the conical flow; this case corresponds to a jet confined by a nonrelativistic adiabatic wind. These results provide strong support both to the model of particle-dominated flow for relativistic AGN and galactic jets and to the magnetohydrodynamic model of their origin.

Tony Bell
Cosmic rays, magnetic field, spirals, cavities and beams
Abstract: Cosmic rays (CR) gain energy from diffusive shock acceleration by crossing and re-crossing the shock. High energy CR form an extended precursor to the shock. The high energy CR interact with the background plasma upstream of the shock through the jxB force of the electric current j carried by the CR crossing the magnetic field B frozen into the background plasma. The consequences of the interaction in the precursor are:

Magnetic field lines are stretched resulting in magnetic field amplification.

The amplified magnetic field strongly scatters CR enabling acceleration to high energy.

The amplified magnetic field adopts an expanding spiral structure which encloses cavities of low magnetic field and low plasma density.

The CR current is focused into the cavities producing CR beams and filaments.

Large scale CR-MHD interactions are possible if the shock expands into a circumstellar wind carrying a magnetic field in the configuration of a Parker spiral. CR drifts can carry the highest energy CR to the poles where cavities are created by the large CR pressure. We can further speculate that CR escape through the polar cavities as relativistic beams.

Vasily Beskin
Effective particle acceleration in relativistic and nonrelativistic outflows
Abstract: Effective particle acceleration in the paraboloidal magnetic field demonstrates only the possibility of the almost full energy transformation from electromagnetic field to outgoing relativistic plasma. We discuss whether the necessary conditions can be realized in reality. For non-relativistic outflow it is demonstrated that near the base of the cylindrical jet the shock wave is to take place.

Geoffrey Bicknell
Linkage between Accretion Disks and Blazars
Abstract: Magnetic Fields mediate both turbulent accretion into black holes and the launching of relativistic jets. Using a theory for magnetized accretion developed by Kuncic and Bicknell one can estimate the magnetic field in an accretion disk as a function of the accretion rate. One can then extrapolate this magnetic field to the high energy emission region of a blazar using a model for the initial propagation of a relativistic, Poynting-dominated jet. The comparison of these two estimates provides us with checks on the physics of magnetic accretion, jet propagation and blazar emission. Models for blazar emission also involve different assumptions on the source of the soft photons that are upscattered to high energies. In this paper, estimates of the magnetic fields in a number of blazars obtained from Synchrotron Self Compton (SSC) and Local Inverse Compton (LIC) models are compared with the disk extrapolated values. (LIC emission is a variant of External Inverse Compton emission in which soft photons external to the high energy electrons are generated locally.) Internal consistency with the magnetic field extrapolated from the disk is obtained when the blazar emission is LIC emission.

G.S. Bisnovatyi-Kogan
Jet confinement by magneto-torsional oscillations.
Abstract: Many quasars and active galactic nuclei (AGN) appear in radio, optical, and X-ray maps, as a bright nuclear sources from which emerge single or double long, thin jets. When observed with high angular resolution these jets show structure with bright knots separated by relatively dark regions. High percentages of polarization, sometimes more then 50\% in some objects, indicates the nonthermal nature of the radiation which is well explained as the synchrotron radiation of the relativistic electrons in an ordered magnetic field. We consider magnetic collimation, connected with torsional oscillations of a cylinder with elongated magnetic field. The cylinder has a periodically distributed initial rotation around the cylinder axis. The stabilizing azimuthal magnetic field is created here by torsional oscillations. Approximate simplified model is developed. Ordinary differential equation is derived, and solved numerically, what gives a possibility to estimate quantitatively the range of parameters where jets may be stabilized by torsional oscillations.

Sergey Bogovalov
(poster)
We present a detailed hydrodynamical study of properties of the flow produced by a collision of ultrarelativistic pulsar wind with environment in binary systems. Obtained results show that the collision should result in formation of an "unclosed" (at spatial scales comparable to the binary system size) pulsar wind termination shock even in a case when the stellar wind ram pressure exceeds significantly the pulsar wind kinetical pressure. Moreover, the post-shock flow propagates in a rather narrow region, with very high bulk Lorentz factor. This flow acceleration is related to so-called adiabatical losses, which are purely hydrodynamical effect. Interestingly, in this case, no magnetic field is required for formation of an ultrarelativistic bulk outflow. The obtained results might provide new interpretation of orbital variability of radio, X-ray and gamma-ray signals detected from binary pulsar system PSR~1259-63/SS2883.

Katherine Blundell
Outflows from radio-quiet quasars
Abstract: We present a new model for the radio emission from radio-quiet quasar nuclei. We show that a thermal origin for the high brightness temperature, flat spectrum point sources (known as radio ``cores'') is possible provided the emitting region is hot and optically-thin. We hence demonstrate that optically-thin bremsstrahlung from a slow, dense disk wind can make a significant contribution to the observedlevels of radio core emission. This is a much more satisfactory explanation, particularly for sources where there is no evidence of a jet, than a sequence of self-absorbed synchrotron components which collectively conspire to give a flat spectrum. Furthermore, such core phenomena are already observed directly via milli-arcsecond radio imaging of the Galactic microquasar SS433 and the active galaxy NGC\,1068. We contend that radio-emitting disk winds must be operating at some level in radio-loud quasars and radio galaxies as well (although in these cases, observations of the radio cores are frequently contaminated/dominated by synchrotron emission from jet knots). This interpretation of radio core emission mandates mass accretion rates that are substantially higher than Eddington. Moreover, acknowledgment of this mass-loss mechanism as an AGN feedback process has important implications for the input of energy and hot gas into the IGM since it is considerably less directional than that from jets.

Markus Boettcher
The WEBT Campaign on 3C279 in 2006
Abstract: The quasar 3C~279 was the target of an extensive multiwavelength monitoring campaign from January through March 2006. An optical-IR-radio monitoring campaign by the Whole Earth Blazar Telescope (WEBT) collaboration was organized around Target of Opportunity X-ray and soft $\gamma$-ray observations with {\it Chandra} and {\it INTEGRAL}, which were carried out in mid-January 2006, with additional X-ray coverage by {\it RXTE} and {\it Swift} XRT. In this paper we present the results of the WEBT campaign.
The source exhibited substantial variability of flux and spectral shape, in particular in the optical regime, with a characteristic time scale of a few days. The variability patterns throughout the optical BVRI bands were very closely correlated with each other, while there was no obvious correlation between the optical and radio variability. After the trigger flux level for the {\it Chandra} and {\it INTEGRAL} ToOs was reached on Jan. 5, 2006, the flux decayed quasi-exponentially by about one magnitude until the end of the time frame of the X-ray and $\gamma$-ray observations, with a decay time scale of $\tau_d \sim 12.8$~d.
In intriguing contrast to the findings in other (in particular, BL~Lac type) blazars, a discrete correlation function analysis beetween different optical (BVRI) bands indicates a lag of shorter-wavelength behind longer-wavelength variability throughout the well sampled optical bands, with a time delay increasing with increasing frequency difference. This appears to go in tandem with an occasional incidation of counterclockwise spectral hysteresis in a color-intensity diagram (B-R vs. R). Thus, spectral hardening during flares appears delayed with respect to a rising total (optical) flux. This, in combination with the very steep IR-optical continuum spectral index of $\alpha_o \sim 1.75$, may indicate a highly oblique magnetic field configuration near the base of the jet, leading to inefficient particle acceleration and a very steep electron injection spectrum.
As the emission region propagates along the jet, a gradual hardening of the primarily injected ultrarelativistic electron distribution may be caused by the gradual build-up of hydromagnetic turbulence, which would lead to a gradually increasing contribution of second-order Fermi acceleration.
An alternative explanation of this phenomenon may be a slow acceleration mechanism by which relativistic electrons are accelerated on a time scale of several days. However, even though this model can plausibly explain the observed variability trends and overall luminosity of the source, it requires an unusually low magnetic field in the emitting region of $B \lesssim 0.2$~G, about an order of magnitude lower than inferred from previous analyses of simultaneous SEDs of 3C~279 and other flat-spectrum radio quasars with similar properties.

C. Boisson
(poster)
Broad band X-ray spectra of the Seyfert 1 Mkn 841

Pol Bordas
(poster)
Non-thermal emission from microquasar jets interacting with their surroundings
Abstract: We study the high energy processes involved when microquasar jets interact with the ISM, where thermal and non-thermal particle populations can be present. We model the jet/ISM interaction region as a self-similar structure, and we take into account particle acceleration both at the reverse and forward shocks. We focus on the non-thermal emission produced by synchrotron and Inverse Compton (IC) as well as relativistic Bremsstrahlung processes. Different regions of the parameter space are explored and broadband energy spectral distributions (SED) are computed. This allows us to specify under which conditions the multiwavelength radiation from the termination region of microquasar jets may be detectable.

Valenti Bosch-Ramon
On the X-ray/TeV connection in microquasars
Abstract: X-ray binaries with relativistic jets, sometimes referred to as microquasars, are objects in which very energetic phenomena take place. The likely occurrence of strong shocks powered by these outflows, and the presence of dense matter, magnetic and photon fields, render many of these sources very good candidates to produce non-thermal radiation at different wavelengths, as shown by observations. In the X-ray and TeV domain, it is common to look for correlations in the emission at these energies due to a likely physically linked origin: synchrotron and IC emission in leptonic models, neutral pion gamma-rays and secondary radiation in hadronic ones. In this talk, we want to go through the different mechanisms that encompass these keV--TeV connection, trying to give an overview on what may be expected when observing galactic jet sources at these energy bands.

Valenti Bosch-Ramon
Studying the interaction between microquasar jets and their environments
(poster)
Abstract: Collimated relativistic outflows or jets can interact strongly with their environments producing a plethora of observational effects, as those shown by gamma-ray bursts, many extragalactic and some galactic large-scale jets. In galactic sources, strong interactions between jets and stellar winds at binary system scales could occur in high-mass microquasars. We aim here at studying from a dynamical point of view the collision between a hydrodynamical supersonic jet moving mildly relativistically through a dense stellar wind. We have performed numerical 2-dimensional simulations of jets crossing the dense stellar material to study how the jet will be affected in the long term. From the simulation results, we find that jets form strong recollimation shocks where pressure balance with the wind is reached. We discuss on the physical properties of such shocks, and briefly comment on their possible radiative outcomes.

Rolf Buehler / Luigi Costamante
Unique TeV/X-ray flares of PKS 2155-304 in 2006
Abstract: The high-frequency-peaked BL Lac PKS 2155-304 is one of the brightest and best studied VHE gamma ray sources in the southern hemisphere. Since 2002 H.E.S.S. has monitored this source and found it to be in an unusually high state in 2006. On the nights of the 28th and 30th of July 2006, two major outburst occurred, with peak fluxes ~80 times the usual values and well-resolved structures with timescales down to ~200s. On the night of 30th July, six hours of simultaneous, continuous X-ray coverage with CHANDRA were obtained. Here we report on the VHE/X-ray observations of these two nights.

Nicolas Camus
(poster)
MHD origin of the Crab Nebula wisps
Abstract: We present the results of new high-resolution relativistic MHD simulations of Pulsar Wind Nebulae (PWN). The simulations reveal highly dynamic structure of the termination shock and the post-shock flow with small-scale vortexes being ejected in the equatorial direction. The most likely origin of the vortexes is the Kelvin-Helmholtz instability in the post-shock shear layers. The original perturbations are created via interaction with unsteady dynamic flow within PWN and they have quite large amplitude from the start. The synchrotron maps shows emission of moving wisps remarkably similar to the wisps of the Crab Nebula.

Christopher Carey
(poster)
MHD kink instability driven by differential rotation
Abstract: Recent observations of extragalactic outflows from active galactic nuclei suggest that some of these jets maintain a large scale helical magnetic structure [1]. The kink instability is known to create similar magnetic structures in laboratory plasmas. Thus, extragalactic jets may resemble a screw pinch topology and be susceptible to the current driven kink instability. We are conducting numerical MHD simulations which will address the issues of collimation and stability of the extragalactic jet system. In these simulations an initial seed field is twisted by a differentially rotating flow boundary condition. Three dimensional nonlinear calculations show that the magnetic column produced is kink unstable and that the instability saturates to a helical magnetic structure. The kink instability in the numerical system leads to conversion of the toroidal magnetic flux, which is injected by the differentially rotating boundary, to poloidal magnetic flux. Examination of this flux conversion process could lead to a better understanding of how the jet distributes magnetic energy to the medium which surrounds it. A synthetic diagnostic is implemented for calculating the synchrotron emission of the numerical jet. This synthetic synchrotron emission is compared to current jet observations, and predictions for future broad band spectroscopic observations of jets are made.

Pietro Cassaro
(poster)
The engine of outflowing in AGN: the role of turbulent physical viscosity
Abstract: Adopting the Smoothed Particle Hydrodynamics (SPH) numerical method we performed a grid of evolving models of a 3D axially symmetric physically viscous accretion disc around a Black Hole (BH) in an AGN. In such disc models, the role of the specific angular momentum $\lambda$ and of the turbulent physical viscosity parameter $\alpha$, according to the Shakura and Sunyaev prescription, are examined. One or two shock fronts develop in the radial inviscid flow, according to the assigned initial kinematic and thermodynamic conditions. Couples of ($\alpha$,$\lambda$) values determine radial periodical oscillations in the shock front. An outflowing can develop from the subsonic post shock region, close to the black hole in some cases. It is evident the link between the accretion disc and the fueling of a jet, through the presence of shock fronts in an accretion disc close to the centrifugal barrier.

Annalisa Celotti
Bulk Comptonization spectra in blazars
Abstract: We study the time dependent spectra produced via the bulk Compton process by a cold, relativistic shell of plasma moving (and accelerating) along the jet of a blazar, scattering on external photons emitted by the accretion disc and reprocessed in the broad line region. Bulk Comptonization of disc photons is shown to yield a spectral component contributing in the far UV band, and would then be currently unobservable. On the contrary, the bulk Comptonization of broad line photons may yield a significant feature in the soft X--ray band. Such a feature is time--dependent and transient, and dominates over the non thermal continuum only when: a) the dissipation occurs close to, but within, the broad line region; b) other competing processes, like the synchrotron self--Compton emission, yield a negligible flux in the X--ray band. The presence of a bulk Compton component may account for the X--ray properties of high redshift blazars that show a flattening (and possibly a hump) in the soft X--rays, previously interpreted as due to intrinsic absorption. We discuss why the conditions leading to a detectable bulk Compton feature might be met only occasionally in high redshift blazars, concluding that the absence of such a feature in the spectra of most blazars should not be taken as evidence against matter--dominated relativistic jets. The detection of such a component carries key information on the bulk Lorentz factor and kinetic energy associated to (cold) leptons. The work is presented in Celotti A., Ghisellini G., Fabian A.C., 2007, MNRAS, 375, 417

Philip Chang
The Long Term Evolution of Magnetic Turbulence in e+e- Shocks
Abstract: I discuss the long term evolution of magnetic fields generated by a collisionless relativistic $e^+e^-$ shock which is initially unmagnetized. Our 2D particle-in-cell numerical simulations show that downstream of such a Weibel-mediated shock, the magnetic energy density, which is initially $\sim (0.1-0.2)$ of the upstream kinetic energy within the shock transition rapidly decays driving the fields to much smaller values.
I explore the hypothesis that the observed damping is a variant of Landau damping in an unmagnetized plasma. Using linear kinetic theory applied to electromagnetic fields in an isotropic, relativistic Maxwellian plasma, we find a simple analytic form for the damping rates, $\gamma_k$, in two and three dimensions for small amplitude, subluminous electromagnetic fields. I discuss the comparison to simulations and limitations of the theory. These results put interesting constraints on synchrotron models for the prompt and afterglow emission from GRBs. We also comment on the relevance of these results for relativistic shocks in electron-ion plasmas.

Philip Chang
(poster)
Long Term Evolution of Magnetic Turbulence in Relativistic e+e- Collisionless Shocks
Abstract: We study the long term evolution of magnetic fields generated by a collisionless relativistic $e^+e^-$ shock which is initially unmagnetized. Our 2D particle-in-cell numerical simulations show that downstream of such a Weibel-mediated shock, particle distributions are close to isotropic, relativistic Maxwellians, and the magnetic turbulence is highly intermittent spatially, with the non-propagating magnetic fields forming relatively isolated regions with transverse dimension $\sim 10-20$ skin depths. These structures decay in amplitude, with little sign of downstream merging. The fields start with magnetic energy density $\sim (0.1-0.2)$ of the upstream kinetic energy within the shock transition, but rapid downstream decay drives the fields to much smaller values, below $10^{-3}$ of equipartition after $\sim 10^3$ skin depths.
In an attempt to construct a theory that follows field decay to these smaller values, we explore the hypothesis that the observed damping is a variant of Landau damping in an unmagnetized plasma. The model is based on the small value of the downstream magnetic energy density, which suggests that particle orbits are only weakly perturbed from straight line motion, if the turbulence is homogeneous. Using linear kinetic theory applied to electromagnetic fields in an isotropic, relativistic Maxwellian plasma, we find a simple analytic form for the damping rates, $\gamma_k$, in two and three dimensions for small amplitude, subluminous electromagnetic fields. We find that magnetic energy does damp due to phase mixing of current carrying particles as $(\omega_p t)^{-q}$ with $q \sim 1$. This overall decay compares well to that found in simulations, since it depends primarily on the longest wavelength modes, $kc/\omega_p \ll 1$. However, the theory predicts overly rapid damping of short wavelength modes. We speculate that magnetic trapping of a substantial fraction of the particles within the highly spatially intermittent downstream magnetic structures may be the origin of this discrepancy. In addition, trapping may form the basis for MHD-like behavior, permitting a small fraction of the initial magnetic energy to persist for times much greater than have been followed in the simulations.
We briefly speculate on other physical processes, which depend on the presence of suprathermal particles, that may cause the generation of longer wavelength magnetic fields that create a magnetized plasma ($kr_{Larmor} \ll 1$), in which the damping is not as fast. However, absent such additional physical processes, we conclude that initially unmagnetized relativistic shocks in electron-positron plasmas are unable to form persistent downstream magnetic fields. These results put interesting constraints on synchrotron models for the prompt and afterglow emission from GRBs. We also comment on the relevance of these results for relativistic shocks in electron-ion plasmas.

Maria Chernyakova
Multiwavelength properties of gamma loud binary systems.
Abstract: Despite the variety of the X-ray binary systems, there are only three firmly established gamma-ray loud binary systems, namely PSR B1259-63, LSI +61 303 and LS 5039. In my talk I will discuss what can we learn from the timing and spectral properties of the broad band emission (from radio to TeV) from these systems.

Paolo Coppi
The Trouble with TeV Blazars
Abstract: In light of the results from recent multi-wavelength campaigns on TeV blazars, I critically re-examine current models for very high energy emission from blazars. I highlight some issues that may be addressed or become important during the upcoming era of combined GLAST-Cherenkov observations.

Paul Dempsey
Effect of Radiative Losses on Particle Acceleration at Relativistic Shocks
Abstract: We investigate the acceleration and simultaneous radiative losses of electrons in the vicinity of relativistic shocks. Particles undergo pitch angle diffusion, gaining energy as they cross the shock by the Fermi mechanism and also emitting synchrotron radiation in the ambient magnetic field. Using a semi-analytic approach we find that the cut-off energy differs greatly from the non-relativistic approximation. Our results also show that, while low energy particles remain nearly isotropic, high energy particles downstream of the shock have a large degree of anisotropy which increases with the Lorentz factor of the shock. The implications for the synchrotron emission of relativistic jets, such as those in microquasars and blazars, are discussed.

Evgeny Derishev
A new mechanism for particle acceleration in relativistic jets
Abstract: We compare different acceleration mechanisms in application to relativistic jets and show that the converter mechanism, suggested recently, is the least sensitive to the geometry of the magnetic field in accelerators and can routinely operate up to cosmic-ray energies close to the fundamental limit. The converter mechanism utilizes multiple conversions of charged particles into neutral ones (protons to neutrons and electrons/positrons to photons) and back by means of photon-induced reactions or inelastic nucleon-nucleon collisions. It works efficiently both in relativistic shocks and in shear flows under the conditions typical for Active Galactic Nuclei, Gamma-Ray Bursts, and microquasars, where it often outperforms the standard diffusive shock acceleration. The main advantages of the converter mechanism in such environments are that it greatly diminishes particle losses downstream and avoids the reduction in the energy gain factor, which normally takes place due to highly collimated distribution of accelerated particles. We also discuss the properties of gamma-ray radiation, which accompanies acceleration of cosmic rays via the converter mechanism and can provide an evidence for the latter. In particular, we point out the fact that the opening angle of the radiation beam-pattern is different at different photon energies, which is relevant to the observability of gamma-ray sources as well as to their timing properties.

Anton Dorodnitsyn
Absorption lines near compact objects. Gravitationally distorted P-Cygni profiles.
Abstract: The formation of spectral lines in an outflow near neutron star or a black hole can be strongly influenced by the gravitational field. We consider a scenario when a resonant absorption in a spectral line takes place in the outflowing plasma within several tens of Schwarzschild radii from the compact object. We compute line profiles from this rapidly moving plasma taking into account both Doppler and gravitational shifting of the photon's frequency. In the following a theory of "P-Cygni" profiles is reconsidered to incorporate the effects of strong gravitational field. In order to compute line profiles we reformulate a concept of equal frequency surfaces in order to account for the gravitational red-shifting. A different topology of such surfaces is found to be a consequence of the strong influence of the gravitational field of the compact object and is dramatically different from that of found in a theory of P-Cygni profiles for normal stars. Possibly the most interesting new feature found is that a spectral line may have multiple absorption and emission features depending on how far the region of interaction is from the compact object and what is the velocity law in the wind. This should be contrasted with the P-Cygni profile that has been widely accepted as a characteristic spectral signature of winds from normal hot stars and which typically consist of emission + blue-shifted absorption feature. We suggest that this property of the line profiles to have complicated absorption components can potentially serve as a tool to study spectroscopically the innermost parts of an outflow and thus to deduce. We discuss finally application of these studies to AGNs and X-ray bursters.

David Eichler
What is the Primary Energy Output in GRBs?
Abstract: A model of GRB is presented and reviewed in which the primary output is gamma radiation. The baryonic outflow is driven by the gamma rays. The model can account for several phenomenogical trends that have been reported

Andy Fabian
Implications of very rapid TeV variability in blazars
Abstract: Rapid, few-minute, variability has been discovered at TeV energies in PKS2155-304 and Mrk501 by the HESS and MAGIC telescopes respectively. The timescales are much shorter than the inferred light-crossing times at the event horizon of the black holes, suggesting that the variability involves enhanced emission in a small region within the outflowing jet. How this might happen, and the constraints imposed on the escape of radiation by photon-photon pair production, will be discussed (see astro-ph/0709.0540).

Christian Fendt
Relativistic MHD simulatioins of jet formation
Abstract: I will first discuss stationary state solutions for MHD jet formation in special and general relativistic MHD. Particular attention is given to the MHD condition in the solutions to the wind equation and how the black hole parameters affects the asymptotic speed of the flow.
I will then discuss results of time-dependent MHD simulation of jet formation from accretion disks applying the special relativistic PLUTO code. Preliminary results show for sufficiently highly magnetized matter launched from a Keplerian disks rotation with v/c = 0.4; jet velocities of v/c= 0.75 could be obtained.

Giovanni Fossati
Challenges to the model for blazar emission from x-ray/tev simultaneous observations
Abstract: Results from the week-long BeppoSAX and RossiXTE campaigns (accompanied by simultaneous TeV observations), and shorter but uninterrupted Chandra observations, depict a portrait of the variability of Mrk421 that is challenging several aspects of the "baseline" SSC model for emission and variability. We observed strong variations in both bands, which are highly correlated, with no evidence of a non-zero X/TeV lags, nor intraband X-ray lags.
During the best observed individual flares the gamma-rays flux scales approximately quadratically with X-ray flux. Moreover, the flux-flux paths during the outbursts decay follow closely those traced in the rising phase.
The synchrotron peak energy correlates very well with the luminosity, over the course of several outbursts. This finding may rule out the possibility that the multiple flares observed during the typical campaign can be modeled as independent "shots", and seems to suggest that in fact they are emitted by a longer-lived "active region" of the jet.
The unprecedented view of the relationships between X-ray and TeV fluxes and spectra afforded by these campaigns, offers a challenge for "mainstream" models, forcing them to new level of detail in the (time-dependent) representation of the source, possibly also towards more "exotic" physical conditions.

Denise Gabuzda
The Magnetic Field Structures of AGN Jets and Possible Connections to their High-Energy Emission
Abstract: The linear polarisation of the parsec-scale jets of Active Galactic Nuclei (AGNs) revealed by VLBI observations provide information about the magnetic (B) fields giving rise to the radio synchrotron radiation. There is now considerable evidence for the presence of helical B fields associated with the jets, which would come about in a natural way via the combined action of rotation of the central black hole/accretion disc and the jet outflow, suggesting an electromagnetic launch mechanism. There are also indications that some compact features in the relativistic flows may be associated with shock compression. In the standard view of the broadband emission of the jets, we might expect very high-energy emission to be generated closer to the active nucleus than the jet radio emission, and possibly to be correlated with the birth/ejection of new VLBI components; however previous studies have provided some evidence that gamma-ray flares detected by EGRET lag behind the extrapolated birth epochs of VLBI components, suggesting the gamma-rays are generated in the jet flow at a substantial distance from the centre of activity.

Neil Gehrels
Gamma Ray Burst Discoveries with SWIFT
Abstract: Gamma-ray bursts are among the most fascinating occurrences in the cosmos. They are thought to be the birth cries of black holes throughout the universe. There has been tremendous recent progress in our understanding of bursts with the new data from the SWIFT mission. SWIFT was launched in November 2004 and is an international multiwavelength observatory designed to determine the origin of bursts and use them to probe the early Universe. Findings from the mission will be presented with emphasis on the relativistic outflows from GRBs. A huge step forward has been made in our understanding of the mysterious short GRBs. High redshift bursts have been detected from enormous explosions early in the universe. GRBs have been found with giant X-ray flares occurring in their afterglow, challenging predictions of the fireball model. These, and other topics, will be discussed.

Gabriele Ghisellini
Emission and power of blazar jets.
Abstract: I will discuss some recent ideas about how and where the jet of blazars can produce the radiation we see, dissipating part of its bulk kinetic power. I will also discuss how these new ideas may be tested through observations, especially at high, MeV to TeV, energies.

Berrie Giebels
Very High Energy gamma-ray observations of Blazars
Abstract: The observational field of extragalactic gamma-ray astronomy has dramatically evolved in the past years, with the new generation of Atmospheric Cherenkov Telescopes (ACTs) such as H.E.S.S., MAGIC and VERITAS coming online, and probing the radiative properties of Active Galactic Nuclei (AGN) with improved levels of sensitivity and spectral resolution. Light curves now show evidence for minute time-scale variability in the very high energy (E>100 GeV) gamma-ray regime, and quality spectra of objects up to z~0.2 are measured, allowing unprecedented constraints to the intrinsic behaviour of these objects, or to the Extragalactic Background Light (EBL) they propagate through.

Jose Gracia
MHD models and synthetic synchrotron maps for the jet of M87
Abstract: In the first part we present a self-consistent MHD model for the jet of M87. The model consist of two distinct zones: an inner relativistic outflow, which we identify with the observed jet, and an outer cold disk-wind. While the former does not self-collimate efficiently due to its high effective inertia, the latter fulfills all the conditions for efficient collimation by the magneto-centrifugal mechanism. Given the right balance between the effective inertia of the inner flow and the collimation efficiency of the outer disk wind, the relativistic flow is magnetically confined into a well collimated beam for a wide range of parameters and matches the measurements of the opening angle of M87 over several orders of magnitude in spatial extent.
In the second part of the talk, we present synthetic synchrotron emission maps for our MHD models. Additional observational constraints break the degeneracy in the MHD parameter space. In principle the two-zone model can reproduce the morphological structure seen in radio observations, as central-peaked profiles across the jet close the the source, limb-bright further down the jet, and a bright knot close to the position of HST-1. However it is difficult to reconcile all features into a single set of parameters.

Jonathan Granot
Opacity Build-up in Impulsive Relativistic Sources
Abstract: Opacity effects in relativistic high-energy gamma-ray sources, such as gamma-ray bursts (GRBs) or Blazars, can probe the Lorentz factor of the outflow and the distance of the emission site from the source, and thus help constrain the composition of the outflow (protons, pairs, magnetic field) and the emission mechanism. While most previous works consider the opacity in steady state, we study the effects of the time dependence of the opacity to pair production ($\gamma\gamma \to e^+e^-$) in an impulsive relativistic source. This may be relevant for the prompt gamma-ray emission in GRBs or flares in Blazars. We present a simple, yet rich, semi-analytic model for the time and energy dependence of the optical depth, $\tau_{\gamma\gamma}$, in which a thin spherical shell expands ultra-relativistically and emits isotropically in its own rest frame over a finite range of radii, $R_0 \leq R \leq R_0 + \Delta R$. This is particularly relevant for GRB internal shocks. We find that in an impulsive source ($\Delta R \lesssim R_0$), while the instantaneous spectrum (which is typically hard to measure due to poor photon statistics) has an exponential cutoff above the photon energy $\epsilon_1(t)$ where $\tau_{\gamma\gamma}(\epsilon_1) = 1$, the time integrated spectrum (which is easier to measure) has a power-law high-energy tail above the photon energy $\epsilon_{1*} \sim \epsilon_1(\Delta t)$ where $\Delta t$ is the duration of the emission episode. Furthermore, photons with energies $\epsilon > \epsilon_{1*}$ are expected to arrive mainly near the onset of the spike in the light curve or flare, which corresponds to the short emission episode. This arises since in such impulsive sources it takes time to build-up the (target) photon field, and thus the optical depth $\tau_{\gamma\gamma}(\epsilon)$ initially increases with time and $\epsilon_1(t)$ correspondingly decreases with time, so that photons of energy $\epsilon > \epsilon_{1*}$ are able to escape the source mainly very early on while $epsilon_1(t) > \epsilon$. As the source approaches a quasi-steady state ($\Delta R \gg R_0$), the time integrated spectrum develops an exponential cutoff, while the power-law tail becomes increasingly suppressed.

Lorraine Hanlon
Properties of gamma-ray bursts observed by INTEGRAL
Abstract: INTEGRAL has localised ~50 gamma-ray bursts to date. We discuss the global characteristics of this sample, using IBIS and SPI data. Spectral properties are determined for a variety of spectral models, including Band, power-law+blackbody and simple power-law. Spectral lags have been determined from the burst time profiles for about half the sample, despite the extreme faintness of many INTEGRAL bursts. INTEGRAL’s sensitivity across the energy range of interest for the prompt burst emission allows us to investigate the hypothesis of a low-luminosity, nearby population of bursts. The azimuthal distribution of double-scatter events in SPI’s germanium detectors, in conjunction with a sophisticated spacecraft and instrument mass model, have been used to place limits on the percentage of polarised emission in the prompt emission of the brightest INTEGRAL bursts.

Sebastian Heinz
Energetics and Particle Content of Microquasar Jets Abstract: Thanks to recent observational advances and new efforts in modeling of large scale jet dynamics, a new framework is emerging within which microquasars appear just as efficient as supermassive black holes in making jets. This seems to hold not just for black holes but for accreting neutron stars as well. Several lines of arguments further suggest that a significant portion of the jet power is dark (i.e., not reflected in the synchrotron-bright leptonic and magnetic components). I will discuss the evidence and future lines of study, as well as the implications for high energy observations of microquasars.

Susumu Inoue
High Energy Emission from Gamma-Ray Bursts
Abstract: We discuss the prospects for prompt GeV-TeV emission from GRBs in view of ongoing and upcoming observations, with emphasis on proton-induced processes and the implications for probing ultra-high-energy cosmic ray acceleration. The related prompt optical emission is also mentioned. We also address how GRB high energy emission may potentially probe important cosmological issues, such as UV radiation fields in the cosmic reionization era, and the nature of magnetic fields in intergalactic voids.

Y. Istomin
(poster)
A two-step mechanism for particle acceleration in the magnetosphere of accreting black holes

Jun Kataoka
Suzaku View of Powerful Gamma-ray Quasars
Abstract: We present the results from multiwavelength campaigns of three powerful gamma-ray quasars, PKS1510-089, RBS315 and Swift J0746 recently organized with Suzaku. Thanks to its low instrumental background, the Suzaku observation provided one of the highes S/N X-ray spectra ever reported between 0.3 and 50 keV. For these quasars, the X-ray spectrum is well represented by an extremely hard power-law with photon index Gamma~ 1.2, but is augmented by an additional soft component apparent below 1 keV for PKS 1510-089, whereas strong deficit of soft photons are observed in RBS 315. We model the broadband spectra of these powerful quasars assuming that the high energy spectral component results from Comptonization of external radiation produced either by dusty torus or the broad line region. In the adopted internal shock scenario, the derived model parameters imply that the power of the jet is dominated by protons but with a number of electrons/positrons exceeding a number of protons by a factor ~10. We also argue that an extremely hard X-ray spectra may result from a double power-law form of the injected electrons, with the break energy G_brk ~ 1000 corresponding to the anticipated threshold of diffusive shock acceleration.

Marina Kaufman-Bernado
Magnetic Field Upper Limits for Jet Formation
Abstract: Very high magnetic fields at the surface of neutron stars or in the accretion disk of black holes inhibit the production of jets. We quantify here the magnetic field strength for the jet formation. By using, the Alfvén Radius, R_A, we study what we call the "basic condition", R_A / R_* = 1 or R_A / R_LSO = 1, in its dependency with the magnetic field strength and the mass accretion rate, and we analyse these results in a 3-D and 2-D plot in the case of neutron star and black hole accretor systems respectively. For this purpose, we did a systematic search of all available observational data of the magnetic field strength and the mass accretion rate. The association of a classical X-ray pulsar (i.e. B ~ 10^12 G) with jets is excluded even if accreting at the Eddington critical rate. Z-sources may develop jets for B ≤ 10^8.2 G whereas Atoll sources are potential sources for jets if B ≤ 10^7.7 G. It is not ruled out that a millisecond X-ray pulsar could develop jets, at least for those sources where B ≤ 10^7.5 G. In this case the millisecond X-ray pulsar could switch to a microquasar phase during its maximum accretion rate. For stellar-mass black hole X-ray binaries, the condition is that B ≤ 1.35 × 10^8 G and B ≤ 5 × 10^8 G at the last stable orbit for a Schwarzschild and a Kerr black hole respectively. For Active Galactic Nuclei it reaches B ≤ 10^5.4 G and B ≤ 10^5.9 G for each kind of black hole. Most of these general and theoretical results are in complete agreement with observational data. Radio emission in classical X-ray pulsars is up to now ruled out (Fender et al. 1997, Fender & Hendry 2000; Migliari & Fender 2006). The magnetic field strength has been determined in a Z-source (Scorpius X-1) using magnetoacoustic oscillations in kHz QPO reaching values of 10^7−8 G (Titarchuck et al. 2001). In the accreting millisecond X-ray pulsar SAX J1808.4-3658 hints for a radio jet have been found (Gaensler et al. 1999).

Stanislav Kelner
(poster)

Dmitry Khangulyan
On the physics of the VHE emission from LS 5039
Abstract: The recent detection of modulated very high energy (VHE) gamma-ray emission from the microquasar LS 5039 at very high energy (VHE) with the HESS array of atmospheric Cherenkov telescopes allows deep theoretical studies of radiation processes in this binary system. Assuming an inverse Compton (IC) origin of the VHE radiation, we performed detailed calculations of the temporal and spatial evolution of the accelerated electrons taking into account the real geometry of the source and asymmetry of the optical radiation of the stellar companion. These effects play crucial role in the formation of the gamma-radiation through the anisotropic Compton scattering and pair-production. We show that for a combination of model parameters we can approximately explain both the energy spectrum of gamma-rays extending to 20 TeV, and the observed modulation of the gamma-ray signal with the orbital period.

Preeti Kharb
Magnetic Fields in Blazar Parsec-scale jets - Possible Connection to Spin Rates of Central Blackholes ?
Abstract: Very long baseline interferometry (VLBI) polarization observations have indicated that while the pc-scale jets in Quasars tend to have magnetic (B) fields aligned with the jet direction, BL Lac objects show a propensity towards perpendicular fields. However, VLBI observations of the subpopulations of the above two classes, viz., the highly polarized quasars (HPQs) and the high-energy-peaked BL Lacs (HBLs) have revealed opposite trends in the B-field geometry. Although the jet polarization electric vectors are spread over 0--90 degrees with respect to the pc-scale jet direction, HPQ jets tend to have perpendicular inferred B-fields while HBL jets tend to possess aligned B-fields. Systematic differences in the total radio power between these subpopulations and their well-studied respective counterparts, viz., the low optically polarized radio quasars (LPRQs) and the low-energy-peaked BL Lacs (LBLs), has prompted us to explore possible connections between the B-field geometry and the spin rates of the central blackholes, which in turn could produce jets with different speeds and different jet velocity structures. We examine this connection using the 1-Jy, HEAO-1 and MOJAVE samples of blazars. We discuss the implications of the different-Spin scenario on the SEDs of these AGNs.

John Kirk
Relativistic shocks in very high brightness temperature sources
Abstract: The theoretical problems posed by sources of synchrotron radiation that appear to have very high brightness temperatures have been puzzling radio astronomers for nearly forty years. The most extreme examples are intra-day variable radio sources. In several cases the cause of the variability is now known to be extrinsic. Nevertheless, observations imply a brightness temperature in excess of 100 TK, well above the conventional inverse Compton limit of 1 TK. I will present a recently developed model based on conventional synchrotron theory applied to an electron distribution function suggested by the dynamics of relativistic shocks.

V.Kocharovsky
Self-consistent current sheets and filaments in relativistic astrophysical plasma.
Abstract: We find analytically a continuous set of stationary current sheets and filaments in collisionless multi-component relativistic plasma using integrals of two-dimensional motion of particles in the self-consistent magnetic field. In our solutions, the magnetic energy density can be comparable to that of particles, and the spatial scale can be arbitrary compared to typical gyroradius of the particles. We consider the properties of newly found stationary solutions and their possible applications to analysis of magnetic field configurations emerging in relativistic astrophysical shocks and jets.

Arieh Koenigl
Oscillatory Radiative Instability of Hydromagnetic Relativistic Shocks
Abstract: The stability of radiative relativistic shocks to global oscillations of the shock-front position and speed is investigated both analytically and numerically in the linear and nonlinear regimes, respectively. The shocks are taken to be plane-parallel and to propagate ultrarelativistically into a proton/electron and/or electron/positron plasma with a transverse magnetic field. The shock emission is assumed to be purely nonthermal and to involve synchrotron radiation and inverse-Compton scattering of the synchrotron photons and possibly also of an external radiation field by locally monoenergetic electrons and positrons. The full covariant equations, including an energy-momentum term for the radiative losses, are utilized in the analysis. The structure of the linear modes is presented and compared with that of the corresponding modes in nonrelativistic, thermally emitting shocks, and the dependence of the linear growth rates and frequencies of the lowest-order overstable modes on the main parameters of the problem is described. Potential applications to AGN jets and gamma-ray burst sources are outlined.

Elmar Koerding
Exploring the disc/jet connection of accreting white dwarfs and black holes
Abstract: I will present a method to estimate accretion power and jet power from the core radio emission of jets. This method allows us to estimate the expected radio luminosity of non-magnetic cataclysmic variables (CVs) in outburst. Radio emission at the predicted level is indeed found in our recent VLA and MERLIN observations of a dwarf novae. We argue that the radio emission originates from a jet, i.e. non-magnetic CVs do show jets unlike previously claimed. A comparison of the radio and optical lightcurve with previous studies of an outburst in the UV and X-rays suggest that the CV jet has the same disk/jet coupling found in outbursts of X-ray binaries. The implications for jet production from compact objects will be discussed. As an additional application of the method to derive accretion rates I will present accretion rate functions of jet emitting active galactic nuclei (AGN) and compare them to the bolometric luminosity function of AGN. Our findings can be explained by a simple model inspired from the analogy between X-ray binaries and AGN.

Serguei Komissarov
Magnetar-energized supernova explosions and GRBs
Abstract: In this talk we present the results of numerical simulations of the evolution of core-collapse supernova explosion following the birth of a magnetar with the dipolar magnetic field of $B=10^{15}$G and the rotational period of $2$ms, The supernova explosion is initiated via introducing into the initial solution the ``radiation bubble'', whose total thermal energy is comparable with the typical energy of supernova ejecta. The numerical models exhibit highly collimated magnetically-driven jets very early on. The jets are super-Alfv\'enic but remain sub-fast until the end of the simulations (t=0.2s). The power released in the jets is about $3\times10^{50}$erg/s which implies the spin-down time of $\simeq 37$s. The total rotational energy of the magnetar, $E\simeq 10^{52}$erg, is sufficient to drive a hypernova but it is not clear as to how large a fraction of this energy can be transfered to the stellar envelope. Given the observed propagation speed of the jets, $v_p\simeq 0.17c$, they are expected to traverse the progenitor in few seconds and after this most of the released rotational energy would be simply carried away by these jets into the surrounding space. Thus we have the first more or less self-consistent numerical model of a central engine capable of producing, in the supernova setting and on a long-term basis, collimated jets with sufficient power to explain long duration GRBs and their afterglows. Although the flow speed of our jets is relatively low, $v_j\simeq 0.5c$, cooling of proto-neutron star will eventually result in much higher magnetization of its magnetospheres and ultra-relativistic asymptotic speeds of the jets. Given the relatively long cooling time-scale we still expect the jets to be only weakly relativistic by the time of break out. This leads to a model of GRB jets with systematic longitudinal variation of Lorentz factor which may have specific observational signatures both in the prompt and the afterglow emission. The simulations also reveal quasi-periodic ejection of plasma clouds into the jet on a time-scale of 20ms related to the large-scale global oscillation of magnetar's magnetosphere caused by the opening-closing of the dead zone field lines. These kind of central engine variability may be partly responsible for the internal shocks of GRB jets and the short-time variability of their gamma-ray emission.

J.P. Lenain
(poster)
SSC scenario for TeV emission from non-blazar AGNs

Amir Levinson
Dissipation and Collimation of Relativistic Jets
Abstract: Opacity constraints imply that the Lorentz factor of the gamma-ray emitting zone in TeV blazars is typically high, in excess of ~ 100 in the most extreme cases. This appears to be in conflict with the much smaller pattern speeds inferred from radio observations. I will discuss the implications of those results to the dynamics of these systems. I will also discuss recent work on collimation of relativistic jets by the pressure and inertia of a surrounding medium, and the role it plays in the dissipation of the bulk energy. Such a mechanism may be an important dissipation channel in blazars microquasars and GRBs, and can naturally account for the presence of stationary radio features in highly relativistic flows. The application of this mechanism to M87, TeV blazars and gamma-ray bursts will be considered.

Alexander Lutovinov
Structure of the Galaxy in Hard X-rays
Abstract: We study a Galaxy structure in a hard X-ray energy band (>20 keV) using data of the INTEGRAL observatory. The increased sensitivity of the survey and very deep observations performed during four years of the observatory operation allow to detect about a hundred new sources significantly enlarged the sample of hard X-ray sources in the Galactic disk and bulge in a comparison with the previous studies. We used the data of ASCA, XMM-Newton, RXTE and INTEGRAL observatories to build the broadband spectra of sources and identified some of them with low or high-mass X-ray binaries. We built the distribution of hard X-ray sources in the Galaxy, constructed their luminosity function and surface density and found that ones are significantly different for the disk and bulge populations. The obtained results are discussed in terms of current models of the formation and evolution of the Galaxy.

Laura Maraschi
The spectral sequence of blazar SEDs revisited
Abstract: The idea that the Spectral Energy Distributions of blazars define a "spectral sequence", whereby the broad band spectral properties change systematically with "observed" radio luminosity was proposed a decade ago on the basis of the then available complete samples of blazars. Deeper surveys and surveys in different energy bands (e.g. hard X-rays) have revealed new blazars, sometimes with "extreme" broad band spectral properties. Thus we revisit the "spectral sequence" concept discussing these new objects also in view of the upcoming GLAST mission. We find that the high redshift, high luminosity blazars, discovered with the BAT/SWIFT and INTEGRAL surveys confirm and extend the "red, high luminosity end" of the spectral sequence. Similarly the new TeV detections confirm the broad band spectral properties of relatively low luminosity blazars (peak synchrotron luminosity below 10^(45) erg/sec). In the intermediate luminosity range, however, some newly discovered/studied blazars suggest a coexistence of different broad band spectral shapes with comparable powers.

Herman Marshall
Modeling the SS 433 Jet Bends
Abstract: We fit Chandra HETGS data obtained for the unusual X-ray binary SS 433. While line strengths and continuum levels hardly change, the jet Doppler shifts show aperiodic variations that probably result from shocks in interactions with the local environment. The X-ray and optical emission line regions are found to be related but not coincident as the optical line emission persists for days while the X-ray emission lines fade in less than 5000 s. The X-ray spectrum of the blue-shifted jet shows over two dozen emission lines from plasma at a variety of temperatures. The emission measure distribution derived from the spectrum can be used to test jet cooling models.

Apostolos Mastichiadis
Compton dragged supercritical piles: The prompt and afterglow scenario
Abstract: We examine the prompt and afterglow emission within the context of the Supercritical Pile model for GRBs. For this we have performed self-consistent calculations by solving three time-dependent kinetic equations for protons, electrons and photons in addition to the usual mass and energy conservation equations. We follow the evolution of the RBW as it sweeps up circumstellar matter and assume that the swept-up electrons and protons have energies no larger than the Lorentz factor of the flow. While the electrons radiate their energies through synchrotron and inverse Compton radiation on short timescales, the protons, at least initially, start accumulating without any dissipation. However, as the accumulated mass of relativistic protons increases they can become supercritical to the `proton-photon pair-production - synchrotron radiation' network, and, as a consequence, they transfer explosively their stored energy to secondary electron-positron pairs and radiation. This results in a burst which has many features similar to the ones observed in GRB prompt emission. At the same time the back-reaction of the radiation on the flow can decelerate it on timescales which are much faster than the ones related to the usual adiabatic/radiative ones. As a result the emission exhibits a steep drop just after the prompt phase, in agreement with the Swift afterglow observations. We show that the above scenario is likely to occur for circumstellar densities not exceeding those expected from a wind of a Wolf-Rayet star. Finally we discuss other features expected within the context of the model like the emission of high energy photons and neutrinos as well as the possibility to account for multiple bursts.

Andrew Melatos
Energy transport and instabilities in wave-like relativistic outflows
Abstract: We review recent theoretical work on the electrodynamics of wave-like relativistic outflows emitted by a rapidly spinning compact object. Particle-in-cell simulations show that a coherent, large-amplitude electromagnetic wave propagates stably within the outflow under a range of conditions, transporting most of the wind energy in the form of oscillatory Poynting flux rather than mechanical energy. Contrary to first expectations, there exist a number of viable formation scenarios if the wave is injected far above the cut-off frequency into an ultrarelativistically streaming plasma. The particles and fields achieve phase coherence within the launch zone without excessive thermalization, via a process that can be understood in terms of adiabatic changes in the plane-wave constants of the motion. (Near the cut-off, electrostatic thermalization disrupts coherence.) The electromagnetic field spectrum and particle distribution function depend on the polarization (linear versus circular) of the "antenna" (i.e. the near zone of the magnetosphere). As the outflow travels away from its source, the Poynting flux is converted gradually to kinetic energy flux by adiabatic mode conversion without significant radiation losses. This offers a possible resolution of the sigma paradox in the Crab pulsar wind. Under certain conditions, parametric instabilities can disrupt this "silent" energy conversion. An observational test of these ideas has been carried out recently with X-ray timing data from the relativistic double pulsar J0737-3039. The absence of orbital modulation of X-rays from the pulsar wind termination shock indicates a high-sigma outflow at the shock, unlike in the Crab pulsar wind. This is consistent with theoretical predictions from the wave-like wind picture. The results are applied briefly to gamma-ray-burster models where the central engine is a rapidly spinning magnetar.

Peter Meszaros
Gamma Ray Bursts as VHE-UHE sources

Sergey Moiseenko
Outflows from magnetorotational supernovae
Abstract: We present results of systematic 2D simulations of core collapse magnetorotational supernovae. The shape and amount of the ejected matter during magnetorotational explosion depends on the initial configuration of the magnetic field, the mass of the core and initial rotation. Increase of the core mass leads to the amplification of the ejected mass and energy during magnetorotational core collapse supernova explosion.

Kostas Moraitis
(poster)
Particle acceleration and gamma-ray emission from AGN jets
Abstract: We study particle acceleration and radiation in the jets of active galactic nuclei (AGN). Although the jet outflow is relativistic, we make the assumption that electrons are accelerated in a shock-front that is moving non-relativistically in the jet frame. Acceleration and energy losses are treated self-consistently through a kinetic equation which also includes particle injection and escape. As a first step we consider only losses from inverse Compton scattering (ICS) of the high energy electrons on the disc photons. The disc model we adopt is of a standard, multi-temperature Shakura-Sunyaev type. The particle distribution function resulting from the solution of the kinetic equation, is convolved with the single particle emissivity for ICS using the full Klein-Nishina cross-section and the emitted spectrum at each height of the jet is obtained. The total spectrum is calculated by integrating the contribution from all heights and then it is compared to high-energy AGN observations.

Gareth Murphy
(poster)
Magnetic Reconnection Phenomenae
Abstract: Magnetic reconnection plays a critical role in many astrophysical processes where high energy emission is observed, e.g. particle acceleration, relativistic accretion powered outflows, pulsar winds and probably in dissipation of Poynting flux in GRBs. The magnetic field acts as a reservoir of energy and can dissipate its energy to thermal and kinetic energy in the tearing mode instability. We have performed 3d nonlinear MHD simulations of the tearing mode instability in a current sheet. Results from a temporal stability analysis in both the linear regime and weakly nonlinear (Rutherford) regime are compared to the numerical simulations. We observe magnetic island formation, island merging and oscillation once the instability has saturated. The growth in the linear regime is exponential in agreement with linear theory. In the second, weakly nonlinear stage (Rutherford stage) the island width grows linearly with time. We find that thermal energy produced in the current sheet strongly dominates the kinetic energy. Finally preliminary analysis indicates a P(k) ~ -4.8 power law for the power spectral density which suggests that the tearing mode vortices play a role in setting up an energy cascade.

Ken-Ichi Nishikawa
Particle acceleration, magnetic field generation, and associated emission in collisionless relativistic jets
Abstract: Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that acceleration occurs within the downstream jet. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The ``jitter'' radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

Michal Ostrowski
Particle acceleration in relativistic jets - shocks, shear layers, ...
Abstract: I will shortly review constraints for the Fermi I acceleration processes in relativistic shocks resulting from the recent modeling by Niemiec et al. (2006a,b). Next I will comment on boundary shear layer acceleration. I also plan to make reference to our observational study of electron acceleration in Cyg A hot spots (Stawarz et al. 2007), may be adding some new staff if ready.

Shane O'Sullivan
(poster)
Parsec-Scale Investigation of the 3D Magnetic Field Structure of Several AGN Jets
Abstract: Preliminary VLBA polarisation results on 6 \u201cblazars\u201d from 6.5-cm to 7- mm are presented here. Observing at several different wavelengths, separated by short and long intervals, enabled reliable information about the magnetic (B) field structure to be obtained and for the effect of Faraday Rotation to be determined and corrected. For all sources the magnitude of the core Rota- tion Measure (RM) derived from the shorter wavelength data was greater than that derived from the longer wavelength data, consistent with a higher elec- tron density and/or B-field strength closer to the central engine. A transverse RM gradient was detected in the jet of 0954+658, providing evidence for the presence of a helical B-field surrounding the jet. The RM in the core region of 2200+420 (BL Lac) displays sign changes in different wavelength intervals (on different spatial scales); we suggest an explanation for this in terms of modest bends in a helical B-field surrounding the jet.

Josep M. Paredes
VHE Gamma Rays from Galactic Binary Systems
Abstract: The detection of TeV gamma-rays by HESS from LS 5039 and the binary pulsar PSR B1259-63 and by MAGIC from LSI+61303 and the black hole Cygnus X-1, provide a clear evidence of very efficient acceleration of particles to multi-TeV energies in X-ray binaries. These observations demonstrate the richness of non-thermal phenomena in compact galactic objects containing relativistic outflows or winds produced near black holes and neutron stars. I review here some of the main observational results on VHE emission from X-ray binaries as well as some of the proposed scenarios to explain the production of very high-energy gamma-rays.

Guy Pelletier
New developments in Fermi acceleration at Relativistic Shocks, UHECRs generation and their possible gamma-ray signature
Abstract: The Fermi cycles at relativistic shocks do not work repeatedly unless an intense MHD turbulence is generated upstream at short scales (usual turbulence cascades from large scales to short scales do not help at all!). Instabilities either in subluminal regime or in superluminal regime will be presented that amplify the magnetic field at short scale and should hopefully allow the Fermi cycles and the formation of the expected power law distribution.
Analysis of the migration of the synchrotron spectrum of GRBs with GLAST together with an Amati's type law should provide interesting constrains on the magnetic field parameters (intensity, decay index, turbulence index and degree of turbulence) during the prompt emission phase. The plausible values based on existing data are already interesting and lead to successful fits of the spectra and light curves. This provides fairly precise informations on the performances of GRBs as particle accelerators. Thus the issue of UHECRs generation during the prompt emission, at the reverse and at the external shocks will be adressed again. A possible gamma diagnosis of the UHECR generation will be proposed.

Jerome Petri
Magnetic reconnection at the termination shock in a striped pulsar wind
Abstract: Most of the rotational luminosity of a pulsar is carried away by a relativistic magnetised wind in which the matter energy flux is negligible compared to the Poynting flux. Near the equatorial plane of an obliquely rotating pulsar magnetosphere, the magnetic field reverses polarity with the pulsar period, forming a wind with oppositely directed field lines. This structure is called a striped wind; dissipation of alternating fields in the striped wind is the object of our study.
The aim of this paper is to study the conditions required for magnetic energy release at the termination shock of the striped pulsar wind. Magnetic reconnection is considered via analytical methods and 1D relativistic PIC simulations.
An analytical condition on the upstream parameters for partial and full magnetic reconnection is derived from the conservation laws of energy, momentum and particle number density across the relativistic shock. Furthermore, by using a 1D relativistic PIC code, we study in detail the reconnection process at the termination shock.
We found a very simple criterion for dissipation of alternating fields at the termination shock, depending on the upstream parameters of the flow. 1D relativistic PIC simulations are in agreement with our criterion. Thus, alternating magnetic fields annihilate easily at relativistic highly magnetised shocks.

Jerome Petri
(poster)
Pulsed high-energy emission and phase-resolved spectral variability in the pulsar striped wind model
Abstract: To date, seven gamma-ray pulsars are known, showing a pulsed emission observed up to tenth of GeV and associated lightcurves with a double-pulse structure. We study this pulsed high-energy emission in the framework of the striped wind model. By numerical integration of the time-dependent emissivity in the current sheet, we compute the phase-dependent spectral variability of the synchrotron and inverse Compton radiation. Several light curves and spectra with phase-resolved dependence are presented. The change in the pulse shape when switching from lower to higher energies is also shown. Pulses are a direct consequence of relativistic beaming. Our model is able to explain some of the high-energy (keV-GeV) spectral features and behavior of several gamma-ray pulsars, like the Crab, Geminga and Vela.

Juri Poutanen
Photon breeding in relativistic jet of blazars: astrophysical implications
Abstract: High-energy photons propagating in the magnetised medium with large velocity gradients can mediate energy and momentum exchange. Conversion of these photons into electron-positron pairs in the field of soft photons with the consequent isotropization and emission of new high-energy photons by Compton scattering can lead to the avalanche of the high-energy photons and pairs fed by the bulk energy of the flow. This is the essence of the photon breeding mechanism.
We study the problem of high-energy emission of relativistic jets in blazars via photon breeding mechanism using 2D ballistic model for the jet with the detailed treatment of particle propagation and interactions. Our numerical simulations from the first principles demonstrate that a jet propagating in the soft radiation field of broad-emission line region can convert a significant fraction of its total power into radiation. The photon breeding mechanism produces a population of high-energy electrons (and positrons) and, therefore, alleviate the need for alternative (Fermi-type) particle acceleration mechanisms that have not yet been shown to produce high-energy leptons self-consistently. The mechanism reproduces basic spectral features observed in blazars including the blazar sequence (shift of spectral peaks towards lower energies at higher luminosities). The significant deceleration of the jet at sub parsec scales reconciles the discrepancy between the high Doppler factors determined by the fits to the spectra of TeV blazars and low apparent velocities observed at VLBI scales. The mechanism produces significantly broader angular distribution of radiation than that predicted by simple model assuming an isotropic emission in the jet frame. This helps to reconcile the observed statistics of FR I and BL Lac objects with the large Lorentz factors of the jets.
We also discuss other possible sites of operation of the photon breeding mechanism and demonstrate that the accretion disc radiation at the scale of about 100 Schwarzschild radii, the dust at a parsec scale, the stellar infrared radiation at kpc scale and the cosmic microwave radiation at 100 kpc scale can serve as targets for photon breeding.

Alexei Pozanenko
Late time afterglow re-brightening of GRB030329: model and observations
Title: Late time afterglow re-brightening of GRB030329: model and observations Abstract: We discuss late time re-brightening of GRB030329 afterglow (jitter episode) starting on about 50th day as an echo results from gamma-rays conversion in a dense molecular cloud. Previously unreleased observations as well as published data in R and B-bands of May-July 2003 are used to fit observed light curve with the model of the dense molecular clouds. In particular we constrain geometry, jet parameters and isotropic energy of the burst. Late time observations of GRB afterglow can be a powerful tool for diagnostic of GRB environment as well as independently restrict jet parameters.

Martin Raue
The new distant TeV blazars: pushing the VHE gamma-ray horizon
Abstract: The discovery of several distant TeV blazars (redshift up to z~0.2 and possibly z~0.5) with the new generation Cherenkov telescopes HESS and MAGIC enables to set strong limits on the extragalactic background light (EBL) in the near to mid-infrared region. These upper limits are only a factor of two to three higher than the lower limits derived from source counts and several theoretical models could already be excluded. Such a low level of the EBL implies that the universe is much more transparent to VHE gamma-rays than previously anticipated. Here we summarize the recent results and discuss future prospects.

Brian Reville
Ion neutral damping of the non-resonant current driven instability
Abstract: We investigate the so-called non-resonant cosmic ray streaming instability, first determined by Bell (2004). We determine the effects of thermal damping and ion-neutral collisions on the growth of this instability. Limits on the growth of the non-resonant mode in SN1006 and RX J1713.7-3946 are presented.

Frank Rieger
Energetic particle acceleration close to the supermassive black hole: the case of M87
Abstract: HESS observations have shown M87 to be a rapidly (time scales of days) variable TeV emitting source. Due to its very low bolometric luminosity, the nucleus of M87 may already be transparent to TeV gamma-rays. We analyse the centrifugal acceleration of charged particles at the base of a rotating jet magnetospheres. It is shown that electrons may be a accelerated to very high Lorentz factors in the vicinity of the light cylinder, allowing inverse Compton upscattering of accretion disk photons to the very high energy domain. The results are compared to the observed spectrum and time variability.

Javier Rico
Observations of microquasar candidates with the MAGIC telescope in the TeV domain
Abstract: MAGIC is a telescope for Very High Energy (VHE, E>100GeV) astronomy. During the first two years of observations it has observed several microquasar candidates. In this talk we will review the most important experimental results obtained, namely, the discovery and detailed study of LS I +61 303 and the evidence of VHE emission from the black-hole X-ray binary Cygnus X-1

Mario Riquelme
Generation of Magnetic Fields by Cosmic Ray Streaming Near Shocks
Abstract: The presence of cosmic rays in the upstream region of astrophysical shocks is expected to substantially amplify the upstream magnetic fields, as inferred from X-ray and radio observations of supernova remnant shocks. Such turbulent fields should further influence the cosmic ray scattering and acceleration in shocks. In this work we present the results of ab-initio numerical simulations of cosmic rays streaming through a magnetized upstream plasma. Using a relativistic Particle-in-Cell (PIC) plasma simulation, we study the growth of magnetic fluctuations in an initially charge and current-neutral plasma consisting of electrons, ions and energetic cosmic rays in one and two dimensions. We find that the dominant mode is a short-wavelength, nonresonant, exponentially growing wave, driven by the current of cosmic rays. We find that this wave can grow from noise and that its growth rate, velocity and polarization are consistent with the linear MHD calculations of Bell (2004, 2005), and, in the relativistic regime, with the kinetic dispersion relation of Reville et al (2007). In 1D, the field growth saturates only when the Larmor radius of cosmic rays becomes comparable to the wavelength of the wave, which would translate to enormous field amplifications in the astrophysical context. In multi-dimensions, however, we find that the instability saturates earlier by the filamentation of the plasma, where cosmic rays are confined to low density cavities surrounded by loops of magnetic field. We discuss the astrophysical implications of these results in the context of magnetic field generation in supernova remnants and in the external shocks of GRBs.

Gustavo E. Romero
LS I +61 303: microquasar or not microquasar?
Abstract: LS I +61 303 is a puzzling object detected from radio up to high-energy gamma-rays. Variability has recently been observed in its high-energy emission. The object is thought to be a binary system, with a compact object and a Be star as primary. The nature of secondary and the origin of the gamma-ray emission is not established at present. Recent VLBA radio data have been used to claim that the system is a Be/neutron star colliding wind binary, instead of a microquasar. We will review the main views on the nature of LS I +61 303 and we will present results of 3D SPH simulations that can shed some light on the nature of the system. Our results support an accretion powered source, compatible with a microquasar interpretation.

Gustavo E. Romero
(poster 1)
Models for gamma-ray production in low-mass microquasars
Abstract: Unlike high-mass systems, low mass microquasars lack external sources of radiation and matter that can help to produce high-energy emission through interactions with relativistic particles. As an alternative, in this work we consider the synchrotron emission of protons and leptons that populate the jet of a low-mass microquasar. Synchrotron photons serve then as a target field for proton-photon and synchrotron self-Compton interactions, yielding a high-energy tail to the spectrum. We also estimate the contribution of the secondary pairs injected through photopair production. Finally, we asses the importance of gamma-gamma absorption.

Gustavo E. Romero
(poster 2)
High-energy emission from massive young stellar objects
Abstract: It is widely established that massive stars are formed inside molecular clouds, but the details of the formation mechanism remain mostly unknown. Recent observations support a picture where there is accretion of matter onto a central protostar with the ejection of molecular outflows that can affect the surrounding medium.
The impact of a supersonic outflow on the ambient gas can produce a strong shock, which might accelerate particles up to relativistic energies. As a result, the jet termination region could be detectable as a non-thermal radio source.
In the present contribution, we study the possible high-energy emission due to the interaction of relativistic particles with the photon and matter fields inside a giant molecular cloud. Electrons lose energy via relativistic Bremsstrahlung and inverse Compton interactions, and protons cool mainly through inelastic collisions with atoms in the cloud. We calculate the spectral energy distribution resulting from all these processes in a particular setting and conclude that massive young stellar objects might be detectable at gamma-rays by forthcoming instruments.

Rita Sambruna
Chandra Jets in radio-loud AGN
Abstract: After 10 years, the Chandra legacy for jets in AGN continues to grow. Several classes of sources were observed so far, including FRIs, FRIIs, and a handful of BL Lacs. I will review the X-ray and multiwavelength properties of jets in these sources, with emphasis on a unified approach.

Reinhard Schlickeiser
Hadronic or primary leptonic origin of high-energy photon emission in compact luminous sources: Clues from spectra and multiwavelength light curves
Abstract: In powerful cosmic nonthermal radiation sources with dominant magnetic field self generation, the generation of magnetic fields at almost equipartition strength by relativistic plasma instabilities operates as fast as the acceleration or injection of ultra-high energy radiating particles in these sources. Consequently, the magnetic field strength becomes time-dependent and adjusts itself to the actual kinetic energy density of the radiating particles in these sources. This coupling of the magnetic field and the magnetic field energy density to the kinetic energy of the radiating particles changes both the synchrotron emissivity and the intrinsic temporal evolution of the relativistic particle energy spectrum after injection. In blazars the nonlinear synchrotron cooling of each particle under equipartition conditions then is orders of magnitude quicker than the linear cooling behaviour in constant magnetic field strength sources. Significant differences in the optically thin synchrotron spectral distributions at different times and in the synchrotron light curves at different frequencies are predicted. If the high-energy gamma-ray emission is produced by hadron synchrotron radiation, the characteristic nonlinear radiative cooling behaviour of hadrons may help to identify cosmic hadron accelerators.

Dan Schwartz
Chandra X-ray Observations of PKS 1055+201
Abstract: A deep, 240 ks observation of the z=1.11 quasar PKS 1055+201, has revealed exceptionally rich X-ray structure. In addition to the X-ray jet coincident with the radio jet, there is an extended X-ray "cocoon" around both the jet and counter jet; and quasi-symmetrical X-ray emission around the quasar. We interpret the latter as emission from gas filling a cluster of galaxies, although the cluster is not otherwise detected. Such a cluster might be responsible for the "swept-back" appearance of jet and counter-jet. A VLA P-band observation reveals 324 MHz emission in the region of the jet and counter-jet qualitatively consistent with the X-ray cocoon. X-ray emission continues at a very weak level to the north, where the radio jet seems to undergo two right angle bends at a terminal hotspot, and then form a diffuse lobe. Interpreting the X-ray emission as inverse Compton scattering on the cosmic microwave background implies that the jet is relativistically beamed toward our direction at an angle no more than 15 deg, and carries a kinetic energy flux about 5 E45 ergs/s if protons have equal energy to the relativistic electrons.

Aneta Siemiginowska
(poster)
X-ray Emission and Broad-Band Spectra of Compact Radio Source. Abstract: We discuss X-ray properties of Compact Radio Sources based on observations performed with Chandra and XMM-Newton. The X-ray spectrum could be related to the radio core or the few arcsec radio structure unresolved in the X-rays. We focus on separating the two emission components. We ale combine available multi-wavelenght data and construct a spectral energy distribution for the compact sources. We also discuss absorption properties in these sources.

Sasha Simic
(poster)
Investigation of element abundances in the surroundings of GRB afterglow Abstract: In the case of high energy collimated outflow it is important to know the density and structure of material through which jet propagate. Here we present a simple study of the environment of GRBs where the relativistic ejecta travel during the event. We use observed spectral lines in the afterglow of gamma ray bursts and by constructing the curve of growth for most red shifted lines, we extract the column densities and Doppler parameter. This can give us the overall picture of abundances in the vicinity of GRBs. Also, we compare this result with the spectral lines with lower redshift to examine the dependence of elemental abundances on the distance from GRB event.

Anatoly Spitkovsky
The Physics of Relativistic Collisionless Shocks
Abstract: Collisionless shocks hold the key to understanding the emission from nonthermal astrophysical sources, including GRBs, pulsar wind nebulae, jets and supernova remnants. I will present a summary of recent progress in first-principles simulations of relativistic collisionless shocks using particle-in-cell codes. The properties of shocks depend on the magnetization of the flow and its composition. I will discuss the internal structure of collisionless shocks in different magnetization regimes, the generation of transient magnetic fields in shocks, and the evolution of magnetic energy in the downstream region. For unmagnetized electron-ion shocks, simulations suggest efficient electron-ion temperature equilibration in the downstream, explaining the high electron energy fraction inferred in GRB afterglows. A particularly exciting result is the development of suprathermal tails due to the Fermi-type acceleration in long-term shock simulations. I will discuss the conditions that are required for the injection of particles into this acceleration process, and the constraints on the efficiency of shock acceleration that can be inferred from simulations.

Jan Staff
(poster)
A three-stage model of GRB inner engine activity in the context of accreting quark stars
Abstract: We describe a model within the ``Quark-nova'' scenario to interpret the recent observations of early X-ray afterglows of long Gamma-Ray Bursts (GRB) with the Swift satellite. This is a three-stage model within the context of a core-collapse supernova. STAGE 1 is an accreting (proto-) neutron star leading to a possible delay between the core collapse and the GRB. STAGE 2 is accretion onto a quark-star, launching an ultrarelativistic jet generating the prompt GRB. This jet also creates the afterglow as the jet interacts with the surrounding medium creating an external shock. Slower shells ejected from the quark star (during accretion), can re-energize the external shock leading to a flatter segment in the X-ray afterglow. STAGE 3, which occurs only if the quark-star collapses to form a black-hole, consists of an accreting black-hole. The jet launched in this accretion process interacts with the preceding quark star jet, and could generate the flaring activity frequently seen in early X-ray afterglows. Alternatively, a STAGE 2b can occur in our model if the quark star does not collapse to a black hole. The quark star in this case can then spins down due to magnetic braking, and the spin down energy may lead to flattening in the X-ray afterglow as well. This model seems to account for both the energies and the timescales of GRBs, in addition to the newly discovered early X-ray afterglow features.

Lukasz Stawarz
Radio Loudness of AGNs: Host Galaxy Morphology and the Spin Paradigm
Abstract: We investigate how the total radio luminosity of AGN-powered radio sources depends on their accretion luminosity and the central black hole mass. We find that AGNs form two distinct and well separated sequences on the radio-loudness - Eddington-ratio plane. We argue that these sequences mark the real upper bounds of radio-loudness of two distinct populations of AGNs: those hosted respectively by elliptical and disk galaxies. Both sequences show the same dependence of the radio-loudness on the Eddington ratio (an increase with decreasing Eddington ratio), which suggests that another parameter in addition to the accretion rate must play a role in determining the jet production efficiency in active galactic nuclei, and that this parameter is related to properties of the host galaxy. The revealed host-related radio dichotomy breaks down at high accretion rates where the dominant fraction of luminous quasars hosted by elliptical galaxies is radio quiet. We argue that the huge difference between the radio-loudness reachable by AGNs in disc and elliptical galaxies can be explained by the scenario according to which the spin of a black hole determines the outflow's power, and central black holes can reach large spins only in early type galaxies (following major mergers), and not (in a statistical sense) in spiral galaxies.

Katrien Steenbrugge
Detection of a relic counterjet in Cygnus A
Abstract: We will present a deep (200 ks co-added) Chandra image of Cygnus A. In particular, we will focus on the detection of a relic counterjet, i.e. the jet receding from the observer. The emission mechanism of the relic counterjet is inverse-Compton off the cosmic microwave background radiation. From the non-detection in X-rays of the relic approaching jet, together with the non-detection of the approaching and receding current radio jets in X-rays, and taking into account the light travel time we will derive the cooling time and other parameters of the jet plasma in Cygnus A. We will discuss the magnetic field strength derived for the relic counterjet and compare it to the previously derived magnetic field strengths for the lobe and hotspots in Cygnus A.

Boris Stern
Gamma-ray emission of blazars as a supercritical process.
Abstract: Supercriticality of the same kind as that in a nuclear pile can take place in high energy astrophysics producing a number of impressive effects. For example, it could cause an explosive release of the energy of a cloud of ultrarelativistic protons into radiation. More certainly, supercriticality should be responsible for dissipation of very energetic relativistic fluids like ultrarelativistic shocks in gamma-ray bursts and jets from active galactic nuclei. In this case works so called converter mechanism which resembles Fermi acceleration with the difference that the momentum is transported back and forth across the boundary between the fluid and external environment in the form of high energy photons rather than charged particles. The mechanism involves such physical processes as photon-photon pair production and Compton scattering which provide the particle reflection from one media back to the other. Under certain conditions which should be satisfied in powerful AGNs the converter mechanism becomes supercritical: high energy photons breed exponentially until their feedback on the fluid change its velocity pattern. Then the system comes to a self-adjusting near-critical steady state. Monte-Carlo simulations with detailed treatment of particle propagation and interactions demonstrate that a jet with Lorentz factor 20 can radiate up to a half of its total energy and up to 80 per cent at Lorentz factor 40. Outer layers of the jet decelerate down to a moderate Lorentz factor (2 - 4) while the center of the jet has the final Lorentz-factor in the range 10 - 20 independently on initial $\Gamma$. Such sharp deceleration under the impact of radiation must cause a number of interesting phenomena like formation of internal shocks and an early generation of turbulence.

Fumio Takahara
A Wien fireball model of relativistic outflows in AGNs
Abstract: We present a new mechanism of the production of relativistic outflows in active galactic nuclei. When copious pair production occurs in a hot accretion flow, optically thin to absorption but optically thick to scattering, the free energy per electron or positron can easily exceed its rest mass. Then, if pairs can escape, they produce an outflow of a large bulk Lorentz factor. We have shown analytically and numerically that this picture holds for spherically symmetric flows of pure pairs. We further simulate outflows of pairs from normal electron-proton plasmas. Using multi-fluid approximation and a Monte Carlo method of radiative transfer, we obtain spherically symmetric, steady solutions of radiation and pair outflows, taking Coulomb scattering into account. We show that powerful but mildly relativistic flow is realized and discuss several possibilities to realize a relativistic flow.

Tadayuki Takahashi
Suzaku Satellites and Observations of High Energy Jet Sources
Abstract: Suzaku is the fifth in a series of Japanese X-ray astronomy satellite with important US instrument contributions. Its scientific payload consists of two kinds of co-aligned instruments, the X--ray Imaging Spectrometers (XIS) and the Hard X--ray Detector (HXD). The HXD extends the bandpass of the observatory to much higher energies with its 10-600 keV bandpass. The detectors onboard Suzaku show the lowest instrumental background, compared with previous missions and thus provides broad band spectra from 0.3 and 50 keV with high S/N ratio in short observation time. During the Peripheral Verification phase and the first AO phase, we have observed high energy peaked and low energy peaked blazars. Here we reports the performance of Suzaku, and the results of blazar observations. Particularly, we present the results of four TeV blazars, Mrk 421, Mrk 501, 1ES1218+304, and 1ES1426+428. Strategy of the keV/TeV campaign for other jet sources, such as micro QSO, will also be presented

Joni Tammi
Wave transmission and hard particle spectra from parallel shocks
Abstract: I review recent results concerning the effects relativistic parallel shocks can have on particle-scattering turbulence, and how this in turn can change the properties of particle acceleration in such shocks. I discuss the possibility of increased compression ratio due to this kind of turbulence transmission, and consider the effects of this additional compression to the efficiency of the first-order Fermi acceleration, and the energy spectra of the accelerated particles. Emphasis is put on the possibility of producing spectral indices that are significantly harder than what are usually expected from the first-order Fermi mechanism, but required by a number of observations. The physical requirements, and their plausibility in real astronomical objects, for this mechanism to have notable effects are also discussed.

Andrew Taylor
(poster)
High-Energy Neutrinos from Astrophysical Accelerators of Cosmic Ray Nuclei
Abstract: Ongoing experimental efforts to detect cosmic sources of high energy neutrinos are guided by the expectation that astrophysical accelerators of cosmic ray protons would also generate neutrinos through interactions with ambient matter and/or photons. However there will be a reduction in the predicted neutrino flux if cosmic ray sources accelerate not only protons but also significant number of heavier nuclei, as is indicated by recent air shower data. We consider plausible extragalactic sources such as active galactic nuclei, gamma-ray bursts and starburst galaxies and demand consistency with the observed cosmic ray composition and energy spectrum at Earth after allowing for propagation through intergalactic radiation fields. This allows us to calculate the expected neutrino fluxes from the sources, normalised to the observed cosmic ray spectrum. We find that the likely signals are still within reach of next generation neutrino telescopes such as IceCube.

Olga Toropina
(poster)
MHD simulations of accretion to a magnetized neutron star in the "propeller" regime
Abstract: We investigate accretion to a rotating magnetized star in the "propeller" regime using axisymmetric resistive magnetohydrodynamic simulations. The regime is predicted to occur if the magnetospheric radius is larger than the corotation radius and smaller than the light cylinder radius. We consider two cases: slow moving star and supersonic moving star. In both case simulations show that accreting matter is expelled from the equatorial region of the magnetosphere and that it moves away from the star in a supersonic, disk-shaped outflow. At larger radial distances the outflow slows down and becomes subsonic. Simulations for supersonic moving neutron star indicate that magnetized star spin-down rapidly due to interaction with interstellar medium, faster than for the case of a non-moving star. From many simulation runs we have derived an approximate scaling laws for the angular momentum loss rate.

Yasunobu Uchiyama
Multiwavelength analysis of the large-scale emission in quasar jets
Abstract: We present results from Spitzer infrared observations of relativistic jets in quasars and radio galaxies, and discuss implications for particle acceleration processes operating in AGN jets in the light of multiwavelength analysis. A particular emphasis is placed on discussing our multiwavelength (with VLA, Spitzer, Hubble, and Chandra) analysis of the kiloparsec-scale jet in the well-known quasar 3C 273, which offers new insights into the controversial origin of the X-ray emission seen in many quasar jets. Our analysis suggests that X-rays are produced by the synchrotron process rather than inverse-Compton scattering of CMB photons. We argue that sensitive polarization measurements in the optical will be able to confirm (or reject) this idea.

Susanna Vergani
The interplay of the prompt and afterglow emission in GRB 06041
Abstract: We present simultaneous multi-frequency observations of the afterglow emission of GRB 060418. Thanks to the simultaneous coverage at optical, X-ray and gamma-ray wavelengths, we can detect both the external shock emission (in the optical) and the central engine activity (at higher energies). The two components are clearly distinguished based on temporal and spectral properties. The optical detection of the afterglow onset allow the determination of fundamental fireball properties as the initial fireball Lorentz factor. The X-ray flare closely resemble the prompt emission gamma-ray pulses in their temporal profiles, being wider at low energies and showing lags between the hard and soft bands. The optical-to-gamma-ray SED shows a sharp spectral break, which pinpoint the position of the synchrotron peak frequency and constrains the physical properties of the emitting region.

Susanna Vergani
(poster 1)
Have all short GRBs an associated host galaxy? The case of GRB 070707
Abstract: We present observational results of the MISTICI collaboration on the INTEGRAL GRB 070707. The afterglow light-curve of this short GRB shows a very steep decay after 1-2 days from the trigger, inexplicable by a jetted or high latitude emission. Thanks to very deep ESO-VLT observations, a very faint host galaxy has been detected in R-band with m = 27.3 +/- 0.13. This result confirms that for each short GRB there is an associated host, even if not all the hosts could be detected with ground based observations.

Susanna Vergani
(poster 2)
GRB 070311: a direct link between the prompt emission and the afterglow.
Abstract: We present prompt gamma-ray, early NIR/optical, late optical and X-ray observations of the peculiar GRB 070311 discovered by INTEGRAL, in order to gain clues on the mechanisms responsible for the prompt gamma-ray pulse as well as for the early and late multi-band afterglow of GRB 070311. Notably, the time profile of the late rebrightening can be described as the combination of a time-rescaled version of the prompt gamma-ray pulse and an underlying power law. This result supports a common origin for both prompt and late X-ray/optical afterglow rebrightening of GRB 070311 within the external shock scenario. The main fireball would be responsible for the prompt emission, while a second shell would produce the rebrightening when impacting the leading blastwave in a refreshed shock.

Vasilii Vitrishchak
(poster)
Multi-frequency Circular Polarization Measurements of the VLBI Cores of AGN
Abstract: Apart from the single-epoch, 5 GHz results of Homan, Attridge & Wardle (2001), most parsec-scale measurements of the circular polarization of AGN have been obtained at 15 GHz; results at this latter frequency are now available for about 135 sources, with about 40 having detectable circular polarization on VLBI scales. The parsec-scale circular polarization is nearly always located in the VLBI core region, though several objects with detectable circular polarization in their VLBI jets have also been found. It is generally believed that the circular polarization is likely produced via the Faraday conversion of linear to circular polarization, and recent results of Gabuzda et al. (submitted to MNRAS) suggest that the circular polarization may arise due to this mechanism operating in a helical magnetic-field geometry in the VLBI jets. However, little is known about the frequency dependence of the circular polarization - information that is crucial to understanding the origin of the circular polarization. We present the results of circular polarization measurements for about 40 AGN obtained simultaneously at 15 and 22 GHz using the Very Long Baseline Array.

Nektarios Vlahakis
MHD modeling of relativistic outflows
Abstract: The main characteristics of relativistic, steady, ideal magnetohydrodynamic (MHD) outflows are discussed, focusing on their bulk acceleration and collimation.

Indrek Vurm
(poster)
Title: Electron thermalization and photon emission from compact sources Abstract: We present detailed calculations of the electron thermalization by synchrotron self-absorption accounting for cooling by Compton scattering. For the first time, we solve coupled kinetic equations for electrons and photons without any approximations on the relevant cross-sections and compute self-consistently the resulting electron and photon distributions. Our results may be applied to the magnetized coronae around black hole accretion disks as well as the energetic relativistic outflows that take place in gamma-ray bursts and active galactic nuclei.

Stefan Wagner
Scaling relations for ultrafast gamma-ray flares in Blazars

Victor Zabalza
(poster)
Constraining the orbital variability of LS 5039 through Chandra observations
Abstract: We present the analysis of two 2004 Chandra observations of LS 5039 performed in two different orbital phases during the same orbital cycle. Our results show clear flux variability, showing an increase of flux from orbital phase 0.2 to 0.7, similar to what has been found in other observations within one orbital cycle. We suggest that the X-ray variations are linked to orbital changes of the intrinsic properties of the emitter, and explore its implications on possible emission models taking into account the present multiwavelength knowledge of the source.

Zhibin Zhang
(poster)
Tests for a new GRB luminosity relation
Abstract: We have tested a relative spectral lag (RSL) method suggested earlier as a luminosity/redshift (or distance) estimator, using the generalized method by Schaefer \& Collazzi. We find that behaviors of the luminosities (or redshifts) calculated by the luminosity/redshift-RSL (L/R-RSL) relation are comparable with those of observations. Having applied the luminosity-RSL relation to two different GRB samples, we also find that there exist no violating sources. That is, the relation passes the generalized test successfully including Nakar \& Piran test and Li test. We therefore conclude that the L/R-RSL relation can be a potential tool for cosmological study.