A MULTIWAVELENGTH STUDY OF THE HIGH SURFACE BRIGHTNESS HOT SPOT IN PKS 1421-490

• Main Authors: Godfrey, L. E. H. (Author), Bicknell, G. V. (Author), Lovell, J. E. J. (Author), Jauncey, D. L. (Author), Gelbord, Jonathan (Author), Schwartz, D. A. (Author), Birkinshaw, M. (Author), Georganopoulos, Markos (Author), Murphy, David W. (Author), Perlman, E. S. (Author), Worrall, D. M. (Author), Marshall, Herman (Author)
• Other Authors: MIT Kavli Institute for Astrophysics and Space Research (Contributor), Marshall, Herman Lee (Contributor)
• Format: Article
• Language: English
• Published: Institute of Physics/American Astronomical Society, 2015-03-13T15:52:04Z.
• Subjects: Article
• Online Access: Get fulltext

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 = 3 × 10[superscript 44] ergs s-1, 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 gsim 5.
United States. National Aeronautics and Space Administration
National Science Foundation (U.S.)