Turbulent Cosmic-Ray Reacceleration and the Curved Radio Spectrum of the Radio Relic in the Sausage Cluster

Abstract

It has often been thought that the northern radio relic in the galaxy cluster CIZA J2242.8+5301 (the "Sausage" Cluster) is associated with cosmic ray (CR) electrons that are accelerated at a shock through the diffusive shock acceleration (DSA) mechanism. However, recent radio observations have shown that the radio spectrum is curved, which is inconsistent with the prediction of a simple DSA model. Moreover, the CR electron spectrum before being affected by radiative cooling seems to be too hard for DSA. In this study, we show that these facts are natural consequences if the electrons are reaccelerated in turbulence downstream of the shock. In this model, DSA is not the main mechanism for generating high-energy electrons. We find that the mean free path of the electrons should be much shorter than the Coulomb mean free path for efficient reacceleration. The scale of the turbulent eddies must be smaller than the width of the relic. We also predict hard X-ray spectra of inverse Compton scattering of photons.

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• Merging Cluster Collaboration: A Panchromatic Atlas of Radio Relic Mergers
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• Suzaku observations of the merging galaxy cluster Abell2255: The northeast radio relic
• X-ray study of the double radio relic Abell 3376 with Suzaku
• Magnetic Field Evolution in Giant Radio Relics using the example of CIZA J2242.8+5301
• The Planck clusters in the LOFAR sky VI. LoTSS-DR2: Properties of radio relics
• Shocks and Tides Quantified in the "Sausage" Cluster, CIZA J2242.8+5301, using N-body/hydro-dynamical Simulations
• Multi-Phenomena Modeling of the New Bullet Cluster, ZwCl008.8+52, using N-body/hydrodynamical Simulations
• Particle re-acceleration and diffuse radio sources in the galaxy cluster Abell 1550
• ATCA 16 cm Observation of CIZA J1358.9-4750: Implication of Merger Stage and Constraint on Non-Thermal Properties
• Diffuse radio source candidate in CIZA J1358.9-4750
• The application of the adiabatic compression scenario to the radio relic in the galaxy cluster Abell 3411-3412