Suzaku Measurement of Electron and Magnetic Energy Densities in the East Lobe of the Giant Radio Galaxy DA 240
Abstract
A careful analysis of the Suzaku data of the giant radio galaxy DA 240, of which the size is 1.48 Mpc, revealed diffuse X-ray emission associated with its east lobe. The diffuse X-ray spectrum was described with a simple power-law model with a photon index of Γ = 1.92+0.13-0.17+0.04-0.06, where the first and second errors represent the statistical and systematic ones. The agreement with the synchrotron radio photon index, ΓR = 1.95±0.01 in 326-608.5 MHz, ensures that any excess X-ray emission is attributed to inverse Compton emission from the synchrotron-radiating electrons, boosting up the cosmic microwave background photons. From the X-ray flux density, 51.5±3.9+6.2-5.4 nJy at 1 keV, derived with the photon index fixed at ΓR, in comparison with the synchrotron radio intensity of 10.30±0.12 Jy at 326 MHz, the magnetic and electron energy densities were estimated as um = (3±0.2±0.4) × 10-14 erg cm-3 and ue = (3.4+0.3-0.2+0.5-0.4) × 10-14 erg cm-3 integrated over the electron Lorentz factor of 103-105, respectively. Thus, the east lobe is found to reside in an equipartition condition between the electrons and magnetic field parametrized as ue/um = 1.1+0.2-0.1+0.4-0.2. The east lobe of DA 240 is indicated to exhibit the lowest value of ue, among all of the X-ray detected lobes of radio galaxies. A comparison of the energetics in the giant radio galaxies with a size of ∼1 Mpc to those in the smaller objects suggests a possibility that radio galaxies lose their jet power as they evolve from ∼100 kpc to ∼1 Mpc.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- November 2011
- DOI:
- 10.1093/pasj/63.sp3.S947
- arXiv:
- arXiv:1105.3473
- Bibcode:
- 2011PASJ...63S.947I
- Keywords:
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- galaxies: individual (DA 240);
- magnetic fields;
- radiation mechanism: non-thermal;
- radio continuum: galaxies;
- X-rays: galaxies;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 9 pages, 7 figures, PASJ accepted