Synchrotron X-ray diagnostics of cutoff shape of nonthermal electron spectrum at young supernova remnants. (arXiv:1301.7499v1 [astro-ph.HE])

Synchrotron X-ray diagnostics of cutoff shape of nonthermal electron spectrum at young supernova remnants. (arXiv:1301.7499v1 [astro-ph.HE]):
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.