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Published January 21, 2008 | Published
Journal Article Open

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


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.

Additional Information

©2007 The Authors. Journal compilation ©2007 RAS. Accepted 2007 October 24. Received 2007 October 23; in original form 2007 August 4. We acknowledge M. Markevitch for discussion on XMM–Newton background, and the anonymous reviewer for many constructive suggestions, including the two-step background subtraction method and better presentation of the images in this paper. CMHC thanks Wayne H. Baumgartner for many discussions and advices on SAS, and Ryan C. Ogliore for help interpreting ACE data. We thank the ACE SWEPAM instrument team and the ACE Science Centre for providing the ACE data. This research has made use of SAOIMAGE DS9, developed by the Smithsonian Astrophysical Observatory, and of NASA's Astrophysics Data System.

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