Chandra discovery of extended non-thermal emission in 3C 207 and the spectrum of the relativistic electrons

Free access article

Issue		A&A Volume 381, Number 3, January III 2002


Page(s)		795 - 809
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20011462

A&A 381, 795-809 (2002)
DOI: 10.1051/0004-6361:20011462

Chandra discovery of extended non-thermal emission in 3C 207 and the spectrum of the relativistic electrons

G. Brunetti^{1, 2}, M. Bondi², A. Comastri³ and G. Setti^{1, 2}

¹ Dipartimento di Astronomia, via Ranzani 1, 40127 Bologna, Italy
² Istituto di Radioastronomia del CNR, via Gobetti 101, 40129 Bologna, Italy
³ Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy

(Received 2 August 2001 / Accepted 18 October 2001)

Abstract
We report on the Chandra discovery of large scale non-thermal emission features in the double lobed SSRL quasar 3C 207 ( z=0.684). These are: a diffuse emission well correlated with the western radio lobe, a bright one sided jet whose structure coincides with that of the eastern radio jet and an X-ray source at the tip of the jet coincident with the hot spot of the eastern lobe. The diffuse X-ray structure is best interpreted as inverse Compton (IC) scattering of the IR photons from the nuclear source and provides direct observational support to an earlier conjecture (Brunetti et al. 1997) that the spectrum of the relativistic electrons in the lobes of radio galaxies extends to much lower energies than those involved in the synchrotron radio emission. The X-ray luminous and spatially resolved knot along the jet is of particular interest: by combining VLA and Chandra data we show that a SSC model is ruled out, while the X-ray spectrum and flux can be accounted for by the IC scattering of the CMB photons (EIC) under the assumptions of a relatively strong boosting and of an energy distribution of the relativistic electrons as that expected from shock acceleration mechanisms. The X-ray properties of the hot spot are consistent with a SSC model. In all cases we find that the inferred magnetic field strength are lower, but close to the equipartition values. The constraints on the energy distribution of the relativistic electrons, imposed by the X-ray spectra of the observed features, are discussed. To this aim we derive in the Appendices precise semi-analytic formulae for the emissivities due to the SSC and EIC processes.

Key words: radiation mechanisms: non-thermal -- galaxies: active -- quasars: individual: 3C 207 -- galaxies: jets -- radio continuum: galaxies -- X-rays: galaxies

Offprint request: G. Brunetti, gbrunetti@astbol.bo.cnr.it

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