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Issue A&A
Volume 372, Number 3, June IV 2001
Page(s) 755 - 767
Section Cosmology (including clusters of galaxies)
DOI 10.1051/0004-6361:20010484



A&A 372, 755-767 (2001)
DOI: 10.1051/0004-6361:20010484

Anisotropic inverse Compton scattering in powerful radio galaxies: The case of 3C 295

G. Brunetti1, 2, M. Cappi3, G. Setti1, 2, L. Feretti2 and D. E. Harris4

1  Dipartimento di Astronomia, via Ranzani 1, 40126 Bologna, Italy
2  Istituto di Radioastronomia del CNR, via Gobetti 101, 40129 Bologna, Italy
3  Istituto TeSRE-CNR, Via Gobetti 101, 40129 Bologna, Italy
4  Harvard-Smithsonian Center for Astrophysics, 60 Garden st., Cambridge, MA 02138, USA

(Received 11 December 2000 / Accepted 29 March 2001)

Abstract
Inverse Compton (IC) scattering of nuclear photons with relativistic electrons in the lobes of powerful radio galaxies and quasars can give detectable extended X-ray emission from the radio lobes if relativistic electrons with a Lorentz factor $\gamma < 300$ are present (Brunetti et al. 1997). In general these electrons are not detected since they emit synchrotron radiation at frequencies below the radio band, so that the study of this effect provides a unique tool to measure the energy distribution of the electron population in the radio lobes at $\gamma < 1000$ energies. In this paper we reanalyze the Chandra observation of the powerful and compact radio galaxy 3C 295 for which the IC scattering of nuclear photons is expected to be an important mechanism. We find strong evidence for extended and asymmetrical X-ray emission associated with the radio lobes in the energy band 0.1-2 keV. We show that both the luminosity and morphology of the extended X-ray emission associated with the radio lobes, not compatible with other X-ray mechanisms, can be best interpreted by the IC scattering with nuclear photons. We also show that the relativistic electron energy distribution obtained from the synchrotron radio emission can be extrapolated down to $\gamma \sim 100$ thus providing a first direct evidence on the electron spectrum in the lobes down to lower energies.


Key words: radiation mechanisms: non-thermal -- galaxies: active -- galaxies: individual: 3C 295 -- galaxies: magnetic fields -- radio continuum: galaxies -- X-rays: galaxies

Offprint request: G. Brunetti, gbrunetti@astbo1.bo.cnr.it

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