THE DIFFUSE, RELIC RADIO-SOURCE IN ABELL85 - ESTIMATION OF CLUSTER-SCALE MAGNETIC-FIELD FROM INVERSE COMPTON X-RAYS

We report the first detection of an inverse Compton X-ray emission, sp atially correlated with a very steep spectrum radio source (VSSRS), 00 38-096, without any detected optical counterpart, in cluster Abell 85, The ROSAT PSPC data and its multiscale wavelet analysis reveal a larg e-scale (linear diameter of the order of 500 h(50)(-1) kpc), diffuse X -ray component, in addition to the thermal bremsstrahlung, overlapping an equally large-scale VSSRS. The primeval 3 K background photons, sc attering off the relativistic electrons, can produce the X-rays at the detected level. The inverse Compton flux is estimated to be (6.5 +/- 0.5) x 10(-13) erg s(-1) cm(-2) in the 0.5-2.4 keV X-ray band. A new 3 27-MHz radio map is presented for the cluster field. The synchrotron e mission flux is estimated to be (6.6 +/- 0.90) x 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 l eads to an estimate of (0.95 +/- 0.10) x 10(-6) G for the cluster-scal e magnetic field strength. The estimated field is free of the 'equipar tition' conjecture, the distance, and the emission volume. Further, th e radiative fluxes and the estimated magnetic field imply the presence of 'relic' (radiative lifetime greater than or similar to 10(9) yr) r elativistic electrons with Lorentz factors gamma approximate to 700-17 00; this would be a significant source of radioemission in the hithert o unexplored frequency range nu approximate to 2-10 MHz.