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Title: A powerful double radio relic system discovered in PSZ1 G108.18-11.53: evidence for a shock with non-uniform Mach number?

Diffuse radio emission in the form of radio haloes and relics has been found in a number of merging galaxy clusters. These structures indicate that shock and turbulence associated with the merger accelerate electrons to relativistic energies. We report the discovery of a radio relic + radio halo system in PSZ1 G108.18-11.53 (z = 0.335). This cluster hosts the second most powerful double radio relic system ever discovered. We observed PSZ1 G108.18-11.53 with the Giant Meterwave Radio Telescope and the Westerbork Synthesis Radio Telescope. We obtained radio maps at 147, 323, 607 and 1380 MHz. We also observed the cluster with the Keck telescope, obtaining the spectroscopic redshift for 42 cluster members. From the injection index, we obtained the Mach number of the shocks generating the two radio relics. For the southern shock, we found $M$ = 2.33 $$+0.19\atop{-0.26}$$ while the northern shock Mach number goes from $M$2.20 $$+0.07\atop{-0.14}$$ in the north part down to $M$ = 200 $$+0.03\atop{-0.08}$$ in the southern region. Finally, if the relation between the injection index and the Mach number predicted by diffusive shock acceleration theory holds, this is the first observational evidence for a gradient in the Mach number along a galaxy cluster merger shock.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [5] ;  [1] ;  [1]
  1. Univ. of Hamburg (Germany). Hamburger Sternwarte
  2. National Radio Astronomy Observatory, Socorro, NM (United States)
  3. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  5. Univ. of California, Davis, CA (United States)
Publication Date:
Report Number(s):
LLNL-JRNL-671211
Journal ID: ISSN 0035-8711
Grant/Contract Number:
AC52-07NA27344; NAS8-03060; PF2-130104; AST-0071048; ARI92-14621
Type:
Accepted Manuscript
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Volume: 453; Journal Issue: 4; Journal ID: ISSN 0035-8711
Publisher:
Royal Astronomical Society
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE; National Aeronautic and Space Administration (NASA); German Research Foundation (DFG); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS
OSTI Identifier:
1430998