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

TL;DR

This study uses XMM-Newton X-ray observations to set new limits on the magnetic field strength in relic radio sources 0917+75 and 1401-33, enhancing understanding of their non-thermal emission properties.

Contribution

It provides the first X-ray based constraints on magnetic fields in these relic sources, independent of equipartition assumptions.

Findings

No X-ray emission detected from either relic.

Lower limits on magnetic field strength slightly exceed equipartition estimates.

Adds to the small sample of relics with X-ray observational constraints.

Abstract

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. Due to increasing sensitivity of radio observations, the known population of cluster relics has been growing; however, studies of non-thermal X-ray emission from relics remain scarce. Our study adds to the small sample of relics studied in X-rays. In both relics, our field strength lower limits are slightly larger than estimates of the equipartition magnetic field.