We study the evolution of the energy spectrum of cosmic-ray electrons accelerated at spherically expanding shocks with low Mach numbers and the ensuing spectral signatures imprinted in radio synchrotron emission. Time-dependent simulations of diffusive shock acceleration (DSA) of electrons in the test-particle limit have been performed for spherical shocks with parameters relevant for typical shocks in the intracluster medium. The electron and radiation spectra at the shock location can be described properly by the test-particle DSA predictions with instantaneous shock parameters. However, the volume integrated spectra of both electrons and radiation deviate significantly from the test-particle power-laws, because the shock compression ratio and the flux of injected electrons at the shock gradually decrease as the shock slows down in time. So one needs to be cautious about interpreting observed radio spectra of evolving shocks based on simple DSA models in the test-particle regime.

Abstract
1. INTRODUCTION
2. DSA NUMERICAL SIMULA
    2.1. 1D Spherical CRASH Code
    2.2. Electron Pre-heating and Injection
    2.3. Shock Accelerated CR Electron Spectrum
3. DSA SIMULATION RESULTS
    3.1. Planar versus Spherical Shocks
    3.2. Spherical Shocks with DifferentMagnetic FieldModels
4. SUMMARY
REFERENCES

• Hyesung Kang(Department of Earth Sciences, Pusan National University) Corresponding author