Curved radio spectra of weak cluster shocks

Journal Article · Thu Aug 20 04:00:00 EDT 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/809/2/186· OSTI ID:22882738

Kang, Hyesung ^[1]; Ryu, Dongsu ^[2]

---

1. Department of Earth Sciences, Pusan National University, Pusan 609-735 (Korea, Republic of)
2. 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, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 809; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United Kingdom
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCELERATION
BRIGHTNESS
COMPARATIVE EVALUATIONS
COSMIC DUST
COSMIC RADIATION
DELTA FUNCTION
ELECTRONS
GALAXY CLUSTERS
MACH NUMBER
RELATIVISTIC RANGE
SHOCK WAVES
SPECTRA
SPHERICAL CONFIGURATION