Wuppertal 2015 – scientific programme

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EP: Fachverband Extraterrestrische Physik

EP 9: Astrophysik

EP 9.5: Talk

Thursday, March 12, 2015, 15:45–16:00, G.10.02 (HS 9)

Reacceleration of electrons in supernova remnants — Martin Pohl^{1, 2}, •Alina Wilhelm^{1, 2}, and Igor Telezhinsky^{1, 2} — ¹DESY, 15738 Zeuthen, Germany — ²Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam, Germany

The radio spectra of many shell-type supernova remnants show deviations from those expected on theoretical grounds. In this work we determine the effect of stochastic reacceleration on the spectra of electrons in the GeV band and at lower energies, and we investigate whether or not reacceleration can explain the observed variation of radio spectral indices. 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. Using a synchrotron emissivity that accurately reflects a highly turbulent magnetic field, we calculate the radio spectral index and find that soft spectra with index α ≲ 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.