Discovery of a double radio relic in ZwCl1447.2+2619: A rare testbed for shock acceleration models with a peculiar surface brightness ratio

Abstract

We report a discovery of a double radio relic in the cluster merger ZwCl1447.2+2619 ($z=0.376$) with uGMRT observations at $420\mathrm{MHz}$ and $700\mathrm{MHz}$. The linear sizes of the northern and southern relics are $\sim 0.3$Mpc and $\sim 1.2$Mpc, respectively, which is consistent with the theoretical expectation that a larger relic is produced in the less massive subcluster side. However, ZwCl1447.2+2619 is unlike other known double radio relic systems, where the larger relics are much more luminous by several factors. In this merger the higher surface brightness of the smaller northern relic makes its total radio luminosity comparable to that of the much larger southern relic. The surface brightness ratio $\sim 0.1$ between the two radio relics differs significantly from the relation observed in other double radio relic systems. From our radio spectral analysis, we find that both relics signify similar weak shocks with Mach numbers of $2.9\pm 0.8$ and $2.0\pm 0.7$ for the northern and southern relics, respectively. Moreover, the northern relic is connected to a discrete radio source with an optical counterpart, which indicates the possible presence of cosmic ray injection and re-acceleration. Therefore, we propose that this atypical surface brightness ratio can be explained with the particle acceleration efficiency precipitously dropping in the weak shock regime and/or with re-acceleration of fossil cosmic rays. Our multi-wavelength analysis and numerical simulation suggest that ZwCl1447.2+2619 is a post-merger, which has experienced a near head-on collision $\sim 0.7\mathrm{Gyr}$ ago.

12 pages, 8 figures. accepted to ApJ

References in corpus (24)

• Diffuse Radio Emission from Galaxy Clusters
• Particle Acceleration on Megaparsec Scales in a Merging Galaxy Cluster
• The non-coplanar baselines effect in radio interferometry: The W-Projection algorithm
• The Very Large Array Low-frequency Sky Survey Redux (VLSSr)
• Radio signature of cosmological structure formation shocks
• The Case for Electron Re-Acceleration at Galaxy Cluster Shocks
• Double relics in Abell 2345 and Abell 1240: spectral index and polarization analysis
• A new double radio relic in PSZ1 G096.89+24.17 and a radio relic mass-luminosity relation
• AUTO-MULTITHRESH: A General Purpose Automasking Algorithm
• Deep VLA observations of the cluster 1RXS J0603.3+4214 in the frequency range 1-2 GHz
• Convolution kernels for multi-wavelength imaging
• CAPTURE: A continuum imaging pipeline for the uGMRT
• New mysteries and challenges from the Toothbrush relic: wideband observations from 550 MHz to 8 GHz
• Electron Preacceleration in Weak Quasi-perpendicular Shocks in High-beta Intracluster Medium
• Tempestuous life beyond R_500: X-ray view on the Coma cluster with SRG/eROSITA. I. X-ray morphology, recent merger, and radio halo connection
• Morphology of radio relics I: What causes the substructure of synchrotron emission?
• Revived Fossil Plasma Sources in Galaxy Clusters
• New giant radio sources and underluminous radio halos in two galaxy clusters
• Discovering the most elusive radio relic in the sky: Diffuse Shock Acceleration caught in the act?
• Effects of Multi-scale Plasma Waves on Electron Preacceleration at Weak Quasi-perpendicular Intracluster Shocks
• Exemplary Merging Clusters: Weak-lensing and X-ray Analysis of the Double Radio Relic Merging Galaxy Clusters MACS 1752.0+4440 and ZWCL 1856.8+6616
• Reconstruction of Radio Relics and X-ray Tails in an Off-axis Cluster Merger: Hydrodynamical Simulations of A115
• Radio relics in PSZ2 G096.88+24.18: A connection with pre-existing plasma
• Multiwavelength Analysis of A1240, the Double Radio Relic Merging Galaxy Cluster Embedded in a ~80 Mpc-long Cosmic Filament

Cited by in corpus (4)

• CRESCENDO: An on-the-fly Fokker-Planck Solver for Spectral Cosmic Rays in Cosmological Simulations
• Using the polarization properties of double radio relics to probe the turbulent compression scenario
• A new enigmatic radio relic in the low mass cluster Abell 2108
• Weak-Lensing Analysis of the Complex Cluster Merger Abell 746 with Subaru/Hyper Suprime-Cam