SUZAKU DIAGNOSTICS OF THE ENERGETICS IN THE LOBES OF THE GIANT RADIO GALAXY 3C 35

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(-0.86-0.10)(+0.56+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(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 +/- 5.4(-3.6)(+4.0) nJy with the photon index fixed at the radio value. The X-ray surface brightness from these lobes (similar to 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 +/- 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(e) = (5.8 +/- 2.3(-1.7)(+1.9)) x 10(-14) erg cm(-3) over the electron Lorentz factor of 10(3) - 10(5). The magnetic energy density was calculated as u(m) = (3.1(-1.0-0.9)(+2.5+1.4)) x 10(-14) erg cm(-3), corresponding to the magnetic field strength of 0.88(-0.16-0.14)(+0.31+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.