Radio multifrequency observations of the galaxy cluster pair Abell 399 - 401 with WSRT
Abstract
Galaxy clusters are assembled via merging of smaller structures, in a process that generates shocks and turbulence in the intra cluster medium and produces radio diffuse emission in the form of halos and relics. The cluster pair A 399-A 401 represents a special case: both clusters host a radio halo. Recent Low Frequency Array (LOFAR) observations at 140 MHz revealed the presence of a radio bridge connecting the two clusters along with two relic candidates. These relics include one South of A 399 and the other in between the two clusters, in proximity of a shock front detected in X-ray observations. In this paper we present observations of the A 399-A 401 cluster pair at 1.7, 1.4, 1.2 GHz, and 346 MHz from the Westerbork Synthesis Radio Telescope (WSRT). We detect the radio halo in the A 399 cluster at 346 MHz, extending up to ~650 kpc and with a 125 ± 6 mJy flux density. Its spectral index between 140 MHz and 346 MHz is α = 1.75 ± 0.14. The two candidate relics are also seen at 346 MHz and we determine their spectral indices to be α = 1.10 ± 0.14 and α = 1.46 ± 0.14. The low surface brightness bridge connecting the two clusters is below the noise level at 346 MHz therefore we constrain the bridge average spectral index to be steep, i.e. α > 1.5 at 95 per cent confidence level. This result favours the scenario where dynamically-induced turbulence is a viable mechanism to reaccelerate a population of mildly relativistic particles and amplify magnetic fields on scales of a few Mpcs.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- July 2023
- DOI:
- 10.1093/mnras/stad1158
- arXiv:
- arXiv:2102.02900
- Bibcode:
- 2023MNRAS.522.4421N
- Keywords:
-
- galaxies: clusters: general;
- galaxies: clusters: individual: Abell 399;
- radio continuum: general;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 10 pages, 12 figures