SIMBAD references

We present X-ray observations with the X-ray Multi-Mirror Mission Newton telescope of three double-double radio galaxies (DDRGs). We have detected the core, lobes, and environment of our sample DDRGs in X-rays. We examine the relationships between the radio and X-ray emission and attribute the X-ray emission from the lobes to the inverse Compton scattering of cosmic microwave background photons against the leptons of the radio lobes. The magnetic field strength of the lobes is close to the equipartition value. The X-ray spectrum of the cores of the DDRGs consists of an unabsorbed soft power-law component and no sign of hard power-law components. The soft unabsorbed component is likely to be related to the radio jets. In optical wavebands, there are no strong [O III] lines observed and the host galaxies are not detected in all four bands (namely 2.4, 4.6, 12, 22 µm) of the Wide-Field Infrared Survey Explorer survey. This shows that they are low-excitation radio galaxies. These DDRGs have poor group scale ambient media. We discuss the implications of this observation for models of the episodic activity in DDRGs.