Multiwavelength study of Cygnus A III. Evidence for relic lobe plasma

Journal article

We study the particle energy distribution in the cocoon surrounding Cygnus A, using radio images between 151 MHz and 15 GHz and a 200 ks Chandra ACIS-I image. We show that the excess low frequency emission in the the lobe further from Earth cannot be explained by absorption or excess adiabatic expansion of the lobe or a combination of both. We show that this excess emission is consistent with emission from a relic counterlobe and a relic counterjet that are being re-energized by compression from the current lobe. We detect hints of a relic hotspot at the end of the relic X-ray jet in the more distant lobe. We do not detect relic emission in the lobe nearer to Earth as expected from light travel-time effects assuming intrinsic symmetry. We determine that the duration of the previous jet activity phase was slightly less than that of the current jet-active phase. Further, we explain some features observed at 5 and 15 GHz as due to the presence of a relic jet.

Authors: Steenbrugge, K; Heywood, I; Blundell, K

• Publication status: Published
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 401
• Issue: 1
• Pages: 67-76
• Publication date: 2009-09-06
• DOI: 10.1111/j.1365-2966.2009.15663.x
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: astro-ph.GA; astro-ph.CO