Bulk Lorentz Factor (bulk + lorentz_factor)

Distribution by Scientific Domains


Selected Abstracts


A structure and energy dissipation efficiency of relativistic reconfinement shocks

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2009
Krzysztof Nalewajko
ABSTRACT We present a semi-analytical hydrodynamical model for the structure of reconfinement shocks formed in astrophysical relativistic jets interacting with external medium. We take into account exact conservation laws, both across the shock front and in the zone of the shocked matter, and exact angular relations. Our results confirm a good accuracy of the approximate formulae derived by Komissarov & Falle. However, including the transverse pressure gradient in the shocked jet, we predict an absolute size of the shock to be about twice larger. We calculate the efficiency of the kinetic energy dissipation in the shock and show a strong dependence on both the bulk Lorentz factor and opening angle of the jet. [source]


Extragalactic MeV ,-ray emission from cocoons of young radio galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
M. Kino
ABSTRACT Strong ,-ray emission from cocoons of young radio galaxies is predicted for the first time. Considering the process of adiabatic injection of the shock dissipation energy and mass of the relativistic jet in active nuclei into the cocoon, while assuming thermalizing electron plasma interactions, we find that the thermal electron temperature of the cocoon is typically predicted to be of the order of , MeV, and is determined only by the bulk Lorentz factor of the relativistic jet. Together with the time-dependent dynamics of the cocoon expansion, we find that young cocoons can yield thermal bremsstrahlung emissions at energies ,MeV. [source]


Extended X-ray emission in the high-redshift quasar GB 1508+5714 at z= 4.3

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2003
W. Yuan
ABSTRACT We report the discovery of extended X-ray emission around the powerful high-redshift quasar GB 1508+5714 at z= 4.3, revealed in a long Chandra ACIS observation. The emission feature is 3,4 arcsec away from the quasar core, which corresponds to a projected distance of about 25 kpc. The X-ray spectrum is best fitted with a power law of photon index 1.92 0.35 (90 per cent confidence limit). The X-ray flux and luminosity reach 9.2 10,15 erg cm,2 s,1 (0.5,8 keV) and 1.6 1045 erg s,1 (2.7,42.4 keV rest frame, ,,= 0.73, ,m= 0.27, H0= 71 km s,1 Mpc,1), which is about 2 per cent of the total X-ray emission of the quasar. We interpret the X-ray emission as inverse Compton scattering of cosmic microwave background photons. The scattering relativistic electron population could either be a quasi-static diffuse cloud fed by the jet, or an outer extension of the jet with a high bulk Lorentz factor. We argue that the lack of an obvious detection of radio emission from the extended component could be a consequence of Compton losses on the electron population, or of a low magnetic field. Extended X-ray emission produced by inverse Compton scattering may be common around high-redshift radio galaxies and quasars, demonstrating that significant power is injected into their surroundings by powerful jets. [source]


High energy emission from AGN cocoons in clusters of galaxies

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
M. Kino
Abstract Gamma-ray emission from cocoons of young radio galaxies is predicted. Considering the process of adiabatic injection of the shock dissipation energy and mass of the relativistic jet into the cocoon, we find that the thermal electron temperature of the cocoon is typically predicted to be of the order of ,MeV, and is determined only by the bulk Lorentz factor of the jet. Together with the time-dependent dynamics of the cocoon expansion, we find that young cocoons can yield thermal bremsstrahlung emissions at energies ,MeV. Hotter cocoons (i.e., GeV) for younger sources are also discussed ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Bulk motion of ultrarelativistic conical blazar jets

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006
Gopal-Krishna
ABSTRACT Allowing for the conical shape of ultrarelativistic blazar jets with opening angles of a few degrees on parsec-scales, we show that their bulk Lorentz factors and viewing angles can be much larger than the values usually inferred by combining their flux-variability and proper-motion measurements. This is in accord with our earlier finding that such ultrarelativistic (Lorentz factor, , > 30) conical jets can reconcile the relatively slow apparent motions of Very Long Baseline Interferometry (VLBI) knots in TeV blazars with the extremely fast flows implied by their rapid ,-ray variability. This jet geometry also implies that de-projected jet opening angles will typically be significantly underestimated from VLBI measurements. In addition, de-projected jet lengths will be considerably overestimated if high Lorentz factors and significant opening angles are not taken into account. [source]