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

L. E. H. Godfrey*, G. V. Bicknell, J. E. J. Lovell, D. L. Jauncey, J. Gelbord, D. A. Schwartz, H. L. Marshall, M. Birkinshaw, M. Georganopoulos, D. W. Murphy, E. S. Perlman, D. M. Worrall

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

38 Citations (Scopus)

Abstract

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 similar to 40 kpc from the active galactic nucleus. The isotropic X-ray luminosity of the hot spot, L(2-10) (keV) = 3 x 10(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 (alpha approximate to 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 gamma(min) approximate to 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 Gamma(jet) greater than or similar to 5.

Original languageEnglish
Pages (from-to)707-723
Number of pages17
JournalAstrophysical Journal
Volume695
Issue number1
DOIs
Publication statusPublished - 10 Apr 2009

Keywords

  • galaxies: active
  • galaxies: jets
  • quasars: individual (PKS 1421-490)
  • X-RAY-EMISSION
  • MAGNETOSONIC SHOCK-WAVES
  • POWERFUL RADIO GALAXIES
  • ACTIVE GALACTIC NUCLEI
  • PARTICLE-ACCELERATION
  • CYGNUS-A
  • CHANDRA OBSERVATIONS
  • PHYSICAL CONDITIONS
  • RELATIVISTIC JETS
  • OPTICAL-EMISSION

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