Suzaku diagnostics of the energetics in the lobes of the giant radio galaxy 3C 35

Abstract

The Suzaku observation of a giant radio galaxy 3C 35 revealed faint extended X-ray emission, associated with its radio lobes and/or host galaxy. After careful subtraction of the X-ray and non-X-ray background and contaminating X-ray sources, the X-ray spectrum of the faint emission was reproduced by a sum of the power-law (PL) and soft thermal components. The soft component was attributed to the thermal plasma emission from the host galaxy. The photon index of the PL component, $\Gamma =1.35_{-0.86}^{+0.56}$${}_{-0.10}^{+0.11}$ where the first and second errors represent the statistical and systematic ones, was found to agree with the synchrotron radio index from the lobes, ${\Gamma }_{\mathrm{R}}=1.7$. Thus, the PL component was attributed to the inverse Compton (IC) X-rays from the synchrotron electrons in the lobes. The X-ray flux density at 1 keV was derived as $13.6\pm 5.4_{-3.6}^{+4.0}$ nJy with the photon index fixed at the radio value. The X-ray surface brightness from these lobes ($\sim 0.2$ nJy arcmin${}^{-2}$) is lowest among the lobes studied through the IC X-ray emission. In combination with the synchrotron radio flux density, $7.5\pm 0.2$ Jy at 327.4 MHz, the electron energy density spatially averaged over the lobes was evaluated to be the lowest among those radio galaxies, as $u_{\mathrm{e}}=(5.8\pm 2.3_{-1.7}^{+1.9})\times 10^{-14}$ ergs cm${}^{-3}$ over the electron Lorentz factor of $10^3$ -- $10^5$. The magnetic energy density was calculated as $u_{\mathrm{m}}=(3.1_{-1.0}^{+2.5}$${}_{-0.9}^{+1.4})\times 10^{-14}$ ergs cm${}^{-3}$, corresponding to the magnetic field strength of $0.88_{-0.16}^{+0.31}$${}_{-0.14}^{+0.19}$ $\mu$G. These results suggest that the energetics in the 3C 35 lobes are nearly consistent with equipartition between the electrons and magnetic fields.

10 pages, 8 figures, accepted for ApJ

References in corpus (2)

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• Radio Lobes of Pictor A: an X-ray spatially resolved Study

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