We report the first detection of an inverse Compton X-ray emission , spatially correlated with a very steep spectrum radio source ( VSSRS ) , 0038-096 , without any detected optical counterpart , in cluster Abell 85 .
The ROSAT PSPC data and its multiscale wavelet analysis reveal a large scale ( linear diameter of the order of 500 h ^ { -1 } _ { 50 } kpc ) , diffuse X-ray component , in excess to the thermal bremsstrahlung , overlapping an equally large scale VSSRS .
The primeval 3 K background photons , scattering off the relativistic electrons can produce the X-rays at the detected level .
The inverse Compton flux is estimated to be ( 6.5 \pm 0.5 ) \times 10 ^ { -13 } erg s ^ { -1 } cm ^ { -2 } in the 0.5–2.4 keV X-ray band .
A new 327 MHz radio map is presented for the cluster field .
The synchrotron emission flux is estimated to be ( 6.6 \pm 0.90 ) \times 10 ^ { -14 } erg s ^ { -1 } cm ^ { -2 } in the 10–100 MHz radio band .
The positive detection of both radio and X-ray emission from a common ensemble of relativistic electrons leads to an estimate of ( 0.95 \pm 0.10 ) \times 10 ^ { -6 } G for the cluster-scale magnetic field strength .
The estimated field is free of the ‘ equipartition ’ conjecture , the distance , and the emission volume .
Further , the radiative fluxes and the estimated magnetic field imply the presence of ‘ relic ’ ( radiative lifetime \ga 10 ^ { 9 } yr ) relativistic electrons with Lorentz factors \gamma \approx 700–1700 , that would be a significant source of radio emission in the hitherto unexplored frequency range \nu \approx 2–10 MHz .