Curved Radio Spectra of Weak Cluster Shocks release_nyf547y5ijanvmcpjkcwg5ci4u [as of editgroup_7ymtjomtu5gjvl3vrtl47mvpte]

by Hyesung Kang (1 Pusan National University, Korea, 2 UNIST, Korea)

Released as a article .

2015  

Abstract

In order to understand certain observed features of arc-like giant radio relics such as the rareness, uniform surface brightness, and curved integrated spectra, we explore a diffusive shock acceleration (DSA) model for radio relics in which a spherical shock impinges on a magnetized cloud containing fossil relativistic electrons. Toward this end, we perform DSA simulations of spherical shocks with the parameters relevant for the Sausage radio relic in cluster CIZA J2242.8+5301, and calculate the ensuing radio synchrotron emission from re-accelerated electrons. Three types of fossil electron populations are considered: a delta-function like population with the shock injection momentum, a power-law distribution, and a power-law with an exponential cutoff. The surface brightness profile of radio-emitting postshock region and the volume-integrated radio spectrum are calculated and compared with observations. We find that the observed width of the Sausage relic can be explained reasonably well by shocks with speed u_s ∼ 3× 10^3 and sonic Mach number M_s ∼ 3. These shocks produce curved radio spectra that steepen gradually over (0.1-10) ν_ br with break frequency ν_ br∼ 1 GHz, if the duration of electron acceleration is ∼ 60 - 80 Myr. However, the abrupt increase of spectral index above ∼ 1.5 GHz observed in the Sausage relic seems to indicate that additional physical processes, other than radiative losses, operate for electrons with γ_e ≳ 10^4.
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Type  article
Stage   accepted
Date   2015-07-24
Version   v2
Language   en ?
arXiv  1505.04256v2
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