Constraints on the average magnetic field strength of relic radio sources 0917+75 and 1401-33 from XMM-Newton observations

Understand

We observed two relic radio sources, 0917+75 and 1401-33, with the XMM-Newton X-ray observatory.

• We did not detect any X-ray emission, thermal or non-thermal, in excess of the local background level from either target.
• This imposes new upper limits on the X-ray flux due to inverse Compton scattering of photons from the cosmic microwave background by relativistic electrons in the relic sources, and new lower limits on the magnetic field strength from the relative strength of the radio and X-ray emission.
• The combination of radio and X-ray observations provides a measure of the magnetic field independent of equipartition or minimum energy assumptions.