X-ray Intensity and Polarization Probes of Turbulence in Supernova Remnants
Abstract
The ability of shocks in the outer shells of supernova remnants (SNRs)to accelerate cosmic rays up to the knee above 1 PeV is stronglydependent on the nature of the turbulence in the shock environs. Theparadigm of field enhancement through current-driven instabilities haspromoted high levels of turbulence of unexpectedly strong magneticfields, seeding diffusion near the Bohm limit. The underpinning for ahigh-field scenario was the detection 15 years ago of "thin rims" ofX-ray emission in a handful of young SNRs by Chandra, indicating strongsynchrotron cooling. Radio polarization observations corresponding toGeV electrons suggest lower levels of turbulence. With the prospect ofspatially-resolved X-ray polarimetry for supernova remnants on thehorizon, ushered in by the Imaging X-ray Polarimetry Experiment (IXPE),probes of turbulence using synchrotron signals from 10-100 TeV electronswill soon be possible. This paper explores this prospect, presentingmodels of X-ray intensity and polarization signatures from prescribed turbulence inSNR shocks, and how these couple to MHD turbulence variances. Highervariances naturally depolarize the signal, and roughly linear andquadratic correlations between standard deviations for the Stokesparameters and the MHD variance emerges. These signatures are exploredon both the larger scales of the remnant, and the more confinedsynchrotron rims. For the rim investigation, spatial profiles ofChandra data from SN 1006 and Cas A are employed to constrain theparameters of turbulence at scales corresponding approximately to theangular resolution.
- Publication:
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AAS/High Energy Astrophysics Division
- Pub Date:
- March 2019
- Bibcode:
- 2019HEAD...1710810B