Ryo Yamazaki, Yutaka Ohira, Makoto Sawada, Aya Bamba
Context: The synchrotron X-rays can be a useful tool to investigate the electron acceleration at young supernova remnants (SNRs). Aims: At present, since the magnetic field configuration around the shocks of SNRs is uncertain, it is not clear whether the electron acceleration is limited by SNR age, synchrotron cooling, or even escape from the acceleration region. We study if the acceleration mechanism can be constrained by the cutoff shape of the electron spectrum around the maximum energy. Methods: We derive analytical formulae of the cutoff shape in each case where the maximum electron energy is determined by SNR age, synchrotron cooling and escape from the shock. They are related to the energy dependence of the electron diffusion coefficient. Next, we discuss whether information on the cutoff shape is provided by near future observations which gives simply the photon indices and the flux ratios in the soft and hard X-ray bands. Results: If the power-law index of the electron spectrum is independently determined by other observations, then we can constrain the cutoff shape by comparing theoretical predictions of the photon indices and/or the flux ratios with observed data which will be measured by NuStar and/or Astro-H. Such study is helpful in understanding the acceleration mechanism. In particular, it will bring us another independent constraint on the magnetic field strength around the shocks of SNRs.
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http://arxiv.org/abs/1301.7499
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