TY  - JOUR
A1  - Pohl, Manuela
A1  - Wilhelm, Alina
A1  - Telezhinsky, Igor O.
T1  - Reacceleration of electrons in supernova remnants
T2  - Astronomy and astrophysics : an international weekly journal
N2  - Context. radio spectra of many shell-type supernova remnants show deviations from those expected on theoretical grounds.
 Aims. In this paper we determine the effect of stochastic reacceleration on the spectra of electrons in the GeV band and at lower energies, and we investigate whether reacceleration can explain the observed variation in radio spectral indices.
 Methods. We explicitely calculated the momentum diffusion coefficient for 3 types of turbulence expected downstream of the forward shock: fast-mode waves, small-scale non-resonant modes, and large-scale modes arising from turbulent dynamo activity. After noting that low-energy particles are efficiently coupled to the quasi-thermal plasma, a simplified cosmic-ray transport equation can be formulated and is numerically solved.
 Results. Only fast-mode waves can provide momentum diffusion fast enough to significantly modify the spectra of particles. Using a synchrotron emissivity that accurately reflects a highly turbulent magnetic field, we calculated the radio spectral index and find that soft spectra with index a alpha less than or similar to -0.6 can be maintained over more than 2 decades in radio frequency, even if the electrons experience reacceleration for only one acceleration time. A spectral hardening is possible but considerably more frequency-dependent. The spectral modification imposed by stochastic reacceleration downstream of the forward shock depends only weakly on the initial spectrum provided by, e.g., diffusive shock acceleration at the shock itself.
KW  - acceleration of particles
KW  - turbulence
KW  - cosmic rays
KW  - ISM: supernova remnants
Y1  - 2015
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/39198
SN  - 0004-6361
SN  - 1432-0746
VL  - 574
PB  - EDP Sciences
CY  - Les Ulis
ER  -