Astrophys. J., 695, 707-723 (2009/April-2)
A multiwavelength study of the high surface brightness hot spot in PKS 1421-490.
GODFREY L.E.H., BICKNELL G.V., LOVELL J.E.J., JAUNCEY D.L., GELBORD J., SCHWARTZ D.A., MARSHALL H.L., BIRKINSHAW M., GEORGANOPOULOS M., MURPHY D.W., PERLMAN E.S. and WORRALL D.M.
Abstract (from CDS):
Long Baseline Array imaging of the z = 0.663 broadline radio galaxy PKS 1421-490 reveals a 400 pc diameter high surface brightness hot spot at a projected distance of ∼40 kpc from the active galactic nucleus. The isotropic X-ray luminosity of the hot spot, L_2-10 keV_= 3x1044 ergs/s, is comparable to the isotropic X-ray luminosity of the entire X-ray jet of PKS 0637-752, and the peak radio surface brightness is hundreds of times greater than that of the brightest hot spot in Cygnus A. We model the radio to X-ray spectral energy distribution using a one-zone synchrotron self-Compton model with a near equipartition magnetic field strength of 3 mG. There is a strong brightness asymmetry between the approaching and receding hotspots and the hot spot spectrum remains flat (α ~ 0.5) well beyond the predicted cooling break for a 3 mG magnetic field, indicating that the hotspot emission may be Doppler beamed. A high plasma velocity beyond the terminal jet shock could be the result of a dynamically important magnetic field in the jet. There is a change in the slope of the hotspot radio spectrum at GHz frequencies, which we model by incorporating a cutoff in the electron energy distribution at γmin~ 650, with higher values implied if the hotspot emission is Doppler beamed. We show that a sharp decrease in the electron number density below a Lorentz factor of 650 would arise from the dissipation of bulk kinetic energy in an electron/proton jet with a Lorentz factor Γjet≳ 5.
galaxies: active - galaxies: jets - quasars: individual: PKS 1421-490
Fig. 3: [GBL2009] HSN (Nos HS1, HS2), [GBL2009] JN (No. J1).
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