July 29, 2015 to August 6, 2015
World Forum
Europe/Amsterdam timezone

Reacceleration of electrons in supernova remnants

Aug 4, 2015, 4:00 PM
Amazon Foyer (World Forum)

Amazon Foyer

World Forum

Churchillplein 10 2517 JW Den Haag The Netherlands
Board: 176
Poster contribution CR-TH Poster 3 CR


Prof. Martin Pohl (DESY)


The radio spectra of many shell-type supernova remnants show deviations from those expected on theoretical grounds.}{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. 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. 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 $\alpha \le -0.6$ 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.
Registration number following "ICRC2015-I/" 82
Collaboration -- not specified --

Primary author

Prof. Martin Pohl (DESY)


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