Curved radio spectra of weak cluster shocks
- Department of Earth Sciences, Pusan National University, Pusan 609-735 (Korea, Republic of)
- Department of Physics, UNIST, Ulsan 689-798 (Korea, Republic of)
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 the 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{sub s}∼3×10{sup 3} km s{sup −1} and sonic Mach number M{sub s}∼3. These shocks produce curved radio spectra that steepen gradually over (0.1–10)ν{sub br} with a break frequency ν{sub br}∼1 GHz if the duration of electron acceleration is ∼60–80 Myr. However, the abrupt increase in the 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{sub e}≳10{sup 4}.
- OSTI ID:
- 22882738
- Journal Information:
- Astrophysical Journal, Vol. 809, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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