The XMM-Newton observation of the nearby FR-II radio galaxy 3C 98 is reported .
In two exposures on the target , faint diffuse X-ray emission associated with the radio lobes was significantly detected , together with a bright X-ray active nucleus , of which the 2 – 10 keV intrinsic luminosity is ( 4 – 8 ) \times 10 ^ { 42 } erg s ^ { -1 } .
The EPIC spectra of the northern and southern lobes are reproduced by a single power law model modified by the Galactic absorption , with a photon index of 2.2 _ { ~ { } -0.5 } ^ { ~ { } +0.6 } and 1.7 _ { ~ { } -0.6 } ^ { ~ { } +0.7 } respectively .
These indices are consistent with that of the radio synchrotron spectrum , 1.73 \pm 0.01 .
The luminosity of the northern and southern lobes are measured to be 8.3 _ { ~ { } -2.6 } ^ { ~ { } +3.3 } \times 10 ^ { 40 } erg s ^ { -1 } and 9.2 _ { ~ { } -4.3 } ^ { ~ { } +5.7 } \times 10 ^ { 40 } erg s ^ { -1 } , respectively , in the 0.7 – 7 keV range .
The diffuse X-ray emission is interpreted as an inverse-Compton emission , produced when the synchrotron-emitting energetic electrons in the lobes scatter off the cosmic microwave background photons .
The magnetic field in the lobes is calculated to be about 1.7 ~ { } \mu G , which is about 2.5 times lower than the value estimated under the minimum energy condition .
The energy density of the electrons is inferred to exceed that in the magnetic fields by a factor of 40 – 50 .