Constraints on the cluster environments and hot spot magnetic field strengths of the radio sources 3C 280 and 3C 254

Megan Donahue, Ruth A. Daly, Donald J. Horner

Research output: Contribution to journalReview articlepeer-review

29 Scopus citations


We present new Chandra Observatory observations together with archival Hubble Space Telescope (HST) and radio observations of 3C 254, a radio quasar at z = 0.734, and 3C 280, a radio galaxy at z = 0.996. We report the detection of X-ray and possible HST optical counterparts to the radio hot spots in 3C 280 and the detection of an X-ray counterpart to the western radio hot spot in 3C 254. We present constraints on the presence of X-ray clusters and on the magnetic field strengths in and around the radio hot spots for both targets. Both sources were thought to be in clusters of galaxies based on reports of significant extended emission in ROSAT PSPC and HRI images. The exquisite spatial resolution of the Chandra Observatory allows us to demonstrate that these sources are not in hot, massive clusters. The extended emission seen in ROSAT observations is resolved by Chandra into point sources and is likely to be X-ray emission associated with the radio hot spots of these sources, with possible additional contributions from unrelated point sources. The intergalactic medium around these sources could be dense, but it is demonstrably not dense and hot. We conclude that radio sources are not reliable signposts of massive clusters at moderately high redshifts. We present measurements of the X-ray and optical fluxes of source features and discuss what physical processes may give rise to them. X-ray synchrotron emission could explain the radio, optical, and X-ray hot spot fluxes in 3C 280; this would require continuous acceleration of electrons to high Lorentz factors since the synchrotron lifetime of relativistic electrons that could produce the X-ray emission would be of the order of a human lifetime. Synchrotron self-Compton emission with or without inverse Compton emission due to scattering of the cosmic microwave background radiation can also explain the X-ray emission from the hot spots, although this most likely would require that some other physical process be invoked to explain the optical emission seen in 3C 280. High spatial resolution radio data with broad frequency coverage of the radio hot spot regions are needed to determine which physical process is responsible for the detected X-ray emission and to provide much tighter constraints on the magnetic field strength of the hot spot plasma. We summarize our current constraints on the magnetic field strengths in and around the hot spots of 3C 254 and 3C 280.

Original languageEnglish (US)
Pages (from-to)643-656
Number of pages14
JournalAstrophysical Journal
Issue number2 I
StatePublished - Feb 20 2003

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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