Re-acceleration model for the `Sausage' Radio Relic

Abstract

The Sausage radio relic is the arc-like radio structure in the cluster CIZA J2242.8+5301, whose observed properties can be best understood by synchrotron emission from relativistic electrons accelerated at a merger-driven shock. However, there remain a few puzzles that cannot be explained by the shock acceleration model with only in-situ injection. In particular, the Mach number inferred from the observed radio spectral index, $M_{\mathrm{radio}}\approx 4.6$, while the Mach number estimated from X-ray observations, $M_{\mathrm{X}-\mathrm{ray}}\approx 2.7$. In an attempt to resolve such a discrepancy, here we consider the re-acceleration model in which a shock of $M_s\approx 3$ sweeps through the intracluster gas with a pre-existing population of relativistic electrons. We find that observed brightness profiles at multi frequencies provide strong constraints on the spectral shape of pre-existing electrons. The models with a power-law momentum spectrum with the slope, $s\approx 4.1$, and the cutoff Lorentz factor, ${\gamma }_{e,c}\approx 3-5\times 10^4$ can reproduce reasonably well the observed spatial profiles of radio fluxes and integrated radio spectrum of the Sausage relic. The possible origins of such relativistic electrons in the intracluster medium remain to be investigated further.

12 pages, 5 figures, submittted to JKAS

References in corpus (9)

• Particle Acceleration on Megaparsec Scales in a Merging Galaxy Cluster
• Shock Waves in Eulerian Cosmological Simulations: Main Properties and Acceleration of Cosmic Rays
• Numerical Studies of Diffusive Shock Acceleration at Spherical Shocks
• Re-acceleration Model for Radio Relics with Spectral Curvature
• Shock Waves and Cosmic Ray Acceleration in the Outskirts of Galaxy Clusters
• The widest-frequency radio relic spectra: observations from 150 MHz to 30 GHz
• Multiple density discontinuities in the merging galaxy cluster CIZA J2242.8+5301
• MC^2: Galaxy Imaging and Redshift Analysis of the Merging Cluster CIZA J2242.8+5301
• The highest-frequency detection of a radio relic: 16-GHz AMI observations of the `Sausage' cluster

Cited by in corpus (6)

• Diffuse Radio Emission from Galaxy Clusters
• Electron Preacceleration in Weak Quasi-perpendicular Shocks in High-beta Intracluster Medium
• The Planck clusters in the LOFAR sky VI. LoTSS-DR2: Properties of radio relics
• Shock Acceleration Model for the Toothbrush Radio Relic
• Electron Preacceleration at Weak Quasi-perpendicular Intracluster Shocks: Effects of Preexisting Nonthermal Electrons
• The peculiar cluster MACS J0417.5-1154 in the C and X-bands