Oblique Shock

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Mark Birkinshaw - One of the best experts on this subject based on the ideXlab platform.

  • x ray synchrotron emission from the Oblique Shock in the jet of the powerful radio galaxy 3c 346
    Monthly Notices of the Royal Astronomical Society, 2005
    Co-Authors: D M Worrall, Mark Birkinshaw
    Abstract:

    We report the first detection, with Chandra, of X-ray emission from the jet of the powerful narrow-line radio galaxy 3C 346. X-rays are detected from the bright radio and optical knot at which the jet apparently bends by approximately 70°. The Chandra observation also reveals a bright galaxy-scale atmosphere within the previously known cluster and provides a good X-ray spectrum for the bright core of 3C 346. The X-ray emission from the knot is synchrotron radiation, as seen in lower-power sources. In common with these sources, there is evidence of morphological differences between the radio/optical and X-ray structures, and the spectrum is inconsistent with a one-component continuous-injection model. We suggest that the X-ray-bright knot is associated with a strong Oblique Shock in a moderately relativistic, light jet, at ∼ 20° to the line of sight, and that this Shock is caused by the jet interacting with the wake in the cluster medium behind the companion galaxy of 3C 346. The general jet curvature can result from pressure gradients in the cluster atmosphere.

  • x ray synchrotron emission from the Oblique Shock in the jet of the powerful radio galaxy 3c 346
    arXiv: Astrophysics, 2005
    Co-Authors: D M Worrall, Mark Birkinshaw
    Abstract:

    We report the first detection, with Chandra, of X-ray emission from the jet of the powerful narrow-line radio galaxy 3C 346. X-rays are detected from the bright radio and optical knot at which the jet apparently bends by about 70 degrees. The Chandra observation also reveals a bright galaxy-scale atmosphere within the previously-known cluster, and provides a good X-ray spectrum for the bright core of 3C 346. The X-ray emission from the knot is synchrotron radiation, as seen in lower-power sources. In common with these sources, there is evidence of morphological differences between the radio/optical and X-ray structures, and the spectrum is inconsistent with a one-component continuous-injection model. We suggest that the X-ray-bright knot is associated with a strong Oblique Shock in a moderately relativistic, light jet, at about 20 degrees to the line of sight, and that this Shock is caused by the jet interacting with the wake in the cluster medium behind 3C 346's companion galaxy. The general jet curvature can result from pressure gradients in the cluster atmosphere.

A Meli - One of the best experts on this subject based on the ideXlab platform.

  • particle acceleration in ultra relativistic Oblique Shock waves
    Astroparticle Physics, 2003
    Co-Authors: A Meli, J J Quenby
    Abstract:

    Abstract We perform Monte Carlo simulations of diffusive Shock acceleration at highly relativistic Oblique Shock waves. High upstream flow Lorentz gamma factors ( Γ ) are used, which are relevant to models of ultra-relativistic particle Shock acceleration in active galactic nuclei (AGN) central engines and relativistic jets and gamma ray burst (GRB) fireballs. We investigate numerically the acceleration properties in the relativistic and ultra-relativistic flow regime ( Γ ∼10–10 3 ), such as angular distribution, acceleration time constant, particle energy gain versus number of crossings and spectral shapes. We perform calculations for sub-luminal and super-luminal Shocks. For the first case, the dependence on whether or not the scattering is pitch angle diffusion or large angle scattering is studied. The large angle model exhibits a distinctive structure in the basic power-law spectrum which is not nearly so obvious for small angle scattering. However, both models yield significant ‘speed-up’ or faster acceleration rates when compared with the conventional, non-relativistic expression for the time constant, or alternatively with the time scale r g / c where r g is Larmor radius. The Γ 2 energization for the first crossing cycle and the significantly large energy gain for subsequent crossings as well as the high ‘speed-up’ factors found, are important in supporting the Vietri and Waxman work on GRB ultra-high energy cosmic ray, neutrino and gamma-ray output. Secondly, for super-luminal Shocks, we calculate the energy gain for a number of different inclinations and the spectral shapes of the accelerated particles are given. In this investigation we consider only large angle scattering, partly because of computational time limitations and partly because this model provides the most favourable situation for acceleration. We use high gamma flows with Lorentz factors in the range 10–40, which are relevant to AGN accretion disks and jet ultra-relativistic Shock configurations. We closely follow the particle’s trajectory along the magnetic field lines during Shock crossings where the equivalent of a guiding centre approximation is inappropriate, constantly measuring its phase space co-ordinates in the fluid frames where E =0 . We find that a super-luminal ‘Shock drift’ mechanism is less efficient in accelerating particles to the highest energies observed, compared to the first order Fermi acceleration applying in the sub-luminal case, suggesting that the former cannot stand as a sole acceleration mechanism for the ultra-high energy cosmic rays observed.

  • particle acceleration in ultra relativistic Oblique Shock waves
    arXiv: Astrophysics, 2002
    Co-Authors: A Meli, J J Quenby
    Abstract:

    We perform Monte Carlo simulations of diffusive Shock acceleration at highly relativistic Oblique Shock waves. High upstream flow Lorentz gamma factors are used, which are relevant to models of ultra relativistic particle Shock acceleration in Active Galactic Nuclei (AGN) central engines and relativistic jets and Gamma Ray Burst (GRB) fireballs. We investigate numerically the acceleration properties -in the ultra relativistic flow regime of $\Gamma \sim 10-10^{3}$- such as angular distribution, acceleration time constant, particle energy gain versus number of crossings and spectral shapes. We perform calculations for sub-luminal and super-luminal Shocks, using two different approaches respectively. The $\Gamma^{2}$ energization for the first crossing cycle and the significantly large energy gain for subsequent crossings as well as the high 'speed up' factors found, are important in supporting the Vietri and Waxman models on GRB ultra-high energy cosmic ray, neutrino, and gamma-ray output.

Peter L Biermann - One of the best experts on this subject based on the ideXlab platform.

  • active galactic nuclei jets and multiple Oblique Shock acceleration starved spectra
    Astronomy and Astrophysics, 2013
    Co-Authors: Athina Meli, Peter L Biermann
    Abstract:

    Context. Shocks in jets and hot spots of active galactic nuclei (AGN) are one prominent class of possible sources of very high-energy cosmic-ray particles (above 10 18 eV). Extrapolating their spectrum to their plausible injection energy from some Shock implies an enormous hidden energy for a spectrum of index ∼−2. Some analyses suggest the particles’ injection spectrum at source to be as steep as −2. 4t o−2.7, which exacerbates the problem, by a factor of 10 6 . Nevertheless, it seems implausible that more than at the very best 1/3 of the jet energy goes into the required flux of energetic particles, thus one would need to allow for the possibility that there is an energy problem, which we would like to address in this work. Aims. Sequences of consecutive Oblique Shock features, or conical Shocks, have been theoretically predicted and eventually observed in many AGN jets. Based on that, we use by analogy the Comptonization effect and propose a scenario of a single injection of particles consecutively accelerated by several Oblique Shocks along the axis of an AGN jet. Methods. We developed a test-particle approximation Monte Carlo simulations to calculate particle spectra by acceleration at such a Shock pattern while monitoring the efficiency of acceleration by calculating differential spectra. Results. We find that the first Shock of a sequence of Oblique Shocks establishes a low-energy power-law spectrum with ∼E −2.7 .T he following consecutive Shocks push the spectrum up in energy, rendering flatter distributions with steep cut-offs, and characteristic depletion at low energies, which could explain the puzzling apparent extra source power. Conclusions. Our numerical calculations show a variation of spectral indices, a general spectral flattening, and starved spectra, which connect to the relativistic nature of the Shocks, the multiple Shock acceleration conditions, and the steepness of the magnetic field to the Shock normal. This helps in understanding the jet-magnetic field geometry and the irregular or flat spectra observed in many AGN jets (e.g., CenA, 3C 279, PKS 1510-089). Furthermore, the E −2.4 − E −2.7 ultra-high-energy cosmic-ray injected source spectra claimed by many authors might be explained by the superposition of several, perhaps many, emission sources, all of which end their particle Shock-acceleration sequence with flatter, starved spectra produced by two or more consecutive Oblique Shocks along their jets. It might also imply a mixed component of the accelerated particles above 10 19 eV. Moreover, the present acceleration model can

  • active galactic nuclei jets and multiple Oblique Shock acceleration starved spectra
    arXiv: High Energy Astrophysical Phenomena, 2012
    Co-Authors: Athina Meli, Peter L Biermann
    Abstract:

    Shocks in jets and hot spots of Active Galactic Nuclei (AGN) are one prominent class of possible sources of very high energy cosmic ray particles (above 10^18eV). Extrapolating their spectrum to their plausible injection energy from some Shock, implies an enormous hidden energy for a spectrum of index ~-2. Some analyzes suggest the particles' injection spectrum at source to be as steep as -2.4 to -2.7, making the problem much worse, by a factor of order 10^6. Nevertheless, it seems implausible that more than at the very best 1/3 of the jet energy, goes into the required flux of energetic particles thus, one would need to allow for the possibility that there is an energy problem, which we would like to address in this work. Sequences of consecutive Oblique Shock features, or conical Shocks, have been theorized and eventually observed in many AGN jets. Based on that, we use by analogy the 'Comptonisation' effect and we propose a scenario of a single injection of particles which are accelerated consecutively by several Oblique Shocks along the axis of an AGN jet. We use detailed test-particle approximation Monte Carlo simulations in order to calculate particle spectra by acceleration at such a Shock pattern while monitoring the efficiency of acceleration, calculating differential spectra. We find that the first Shock of a sequence of Oblique Shocks, establishes a low energy power-law spectrum with ~E^-2.7. The consecutive Shocks push the spectrum up in energy, rendering flatter distributions with steep cut-offs and characteristic depletion at low energies, an effect which could explain the puzzling apparent extra source power as well as the flat or inverted spectra from distant flaring sources.

J J Quenby - One of the best experts on this subject based on the ideXlab platform.

  • particle acceleration in ultra relativistic Oblique Shock waves
    Astroparticle Physics, 2003
    Co-Authors: A Meli, J J Quenby
    Abstract:

    Abstract We perform Monte Carlo simulations of diffusive Shock acceleration at highly relativistic Oblique Shock waves. High upstream flow Lorentz gamma factors ( Γ ) are used, which are relevant to models of ultra-relativistic particle Shock acceleration in active galactic nuclei (AGN) central engines and relativistic jets and gamma ray burst (GRB) fireballs. We investigate numerically the acceleration properties in the relativistic and ultra-relativistic flow regime ( Γ ∼10–10 3 ), such as angular distribution, acceleration time constant, particle energy gain versus number of crossings and spectral shapes. We perform calculations for sub-luminal and super-luminal Shocks. For the first case, the dependence on whether or not the scattering is pitch angle diffusion or large angle scattering is studied. The large angle model exhibits a distinctive structure in the basic power-law spectrum which is not nearly so obvious for small angle scattering. However, both models yield significant ‘speed-up’ or faster acceleration rates when compared with the conventional, non-relativistic expression for the time constant, or alternatively with the time scale r g / c where r g is Larmor radius. The Γ 2 energization for the first crossing cycle and the significantly large energy gain for subsequent crossings as well as the high ‘speed-up’ factors found, are important in supporting the Vietri and Waxman work on GRB ultra-high energy cosmic ray, neutrino and gamma-ray output. Secondly, for super-luminal Shocks, we calculate the energy gain for a number of different inclinations and the spectral shapes of the accelerated particles are given. In this investigation we consider only large angle scattering, partly because of computational time limitations and partly because this model provides the most favourable situation for acceleration. We use high gamma flows with Lorentz factors in the range 10–40, which are relevant to AGN accretion disks and jet ultra-relativistic Shock configurations. We closely follow the particle’s trajectory along the magnetic field lines during Shock crossings where the equivalent of a guiding centre approximation is inappropriate, constantly measuring its phase space co-ordinates in the fluid frames where E =0 . We find that a super-luminal ‘Shock drift’ mechanism is less efficient in accelerating particles to the highest energies observed, compared to the first order Fermi acceleration applying in the sub-luminal case, suggesting that the former cannot stand as a sole acceleration mechanism for the ultra-high energy cosmic rays observed.

  • particle acceleration in ultra relativistic Oblique Shock waves
    arXiv: Astrophysics, 2002
    Co-Authors: A Meli, J J Quenby
    Abstract:

    We perform Monte Carlo simulations of diffusive Shock acceleration at highly relativistic Oblique Shock waves. High upstream flow Lorentz gamma factors are used, which are relevant to models of ultra relativistic particle Shock acceleration in Active Galactic Nuclei (AGN) central engines and relativistic jets and Gamma Ray Burst (GRB) fireballs. We investigate numerically the acceleration properties -in the ultra relativistic flow regime of $\Gamma \sim 10-10^{3}$- such as angular distribution, acceleration time constant, particle energy gain versus number of crossings and spectral shapes. We perform calculations for sub-luminal and super-luminal Shocks, using two different approaches respectively. The $\Gamma^{2}$ energization for the first crossing cycle and the significantly large energy gain for subsequent crossings as well as the high 'speed up' factors found, are important in supporting the Vietri and Waxman models on GRB ultra-high energy cosmic ray, neutrino, and gamma-ray output.

B W Van Oudheusden - One of the best experts on this subject based on the ideXlab platform.

  • a parametric study of laminar and transitional Oblique Shock wave reflections
    Journal of Fluid Mechanics, 2018
    Co-Authors: Rogier Giepman, F F J Schrijer, B W Van Oudheusden
    Abstract:

    High-resolution particle image velocimetry measurements were performed on laminar and transitional Oblique Shock wave reflections for a range of Mach numbers (M D 1:6-2:3), Reynolds numbers (Re xsh D 1.4×10 6 -3.5×10 6 ) and flow deflection angles (θ 1°-5° or p3=p1 D 1.11-1.64). The laminar interactions revealed a long, flat and triangular shaped separation bubble. For relatively strong interactions (p3=p1 g 1.2), the bubble grows linearly in the upstream direction with increasing Shock strength. Under these conditions, the boundary layer keeps an on average laminar velocity profile up to the Shock impingement location, followed by a quick transition and subsequent reattachment of the boundary layer. For weaker interactions (p3=p1 l 1.2), the boundary layer is able to remain laminar further downstream of the bubble, which consequently results in a later reattachment of the boundary layer. The pressure distribution at the interaction onset for all laminar cases shows excellent agreement with the free-interaction theory, therefore supporting its validity even for incipiently separated laminar Oblique Shock wave reflections.

  • flow control of an Oblique Shock wave reflection with micro ramp vortex generators effects of location and size
    Physics of Fluids, 2014
    Co-Authors: Rogier Giepman, F F J Schrijer, B W Van Oudheusden
    Abstract:

    This study investigates the influences of micro-ramp size and location on its effectiveness as a flow control device for Oblique Shock wave reflections. The effectiveness is measured in terms of the size of the Shock-induced separation bubble and the reflected Shock unsteadiness. Particle image velocimetry measurements were carried out on the interaction region and the mixing region between micro-ramp and interaction. The separation bubble is shown to be most sensitive to the momentum flux contained in the lower 43% of the incoming boundary layer. The momentum flux added to this region scales linearly with micro-ramp height and larger micro-ramps are shown to be more effective in stabilizing the interaction. Full boundary layer mixing is attained 5.7δ downstream of the micro-ramp and this forms a lower limit on the required distance between micro-ramp and the start of the interaction region. Typical reductions in the average separated area and the Shock unsteadiness of 87% and 51%, respectively, were recorded. Results, however, depend strongly upon the spanwise location, with the micro-ramp being most effective along its centerline.