Turbulent magnetic field amplification driven by cosmic ray pressure gradients
Article first published online: 20 NOV 2012
© 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS
Monthly Notices of the Royal Astronomical Society
Volume 427, Issue 3, pages 2308–2313, 11 December 2012
How to Cite
Drury, L. O'C. and Downes, T. P. (2012), Turbulent magnetic field amplification driven by cosmic ray pressure gradients. Monthly Notices of the Royal Astronomical Society, 427: 2308–2313. doi: 10.1111/j.1365-2966.2012.22106.x
- Issue published online: 20 NOV 2012
- Article first published online: 20 NOV 2012
- Manuscript Accepted: 10 SEP 2012
- Manuscript Received: 10 AUG 2012
- SFI/HEA Irish Centre for High-End Computing (ICHEC)
- magnetic fields;
- ISM: cosmic rays;
- ISM: supernova remnants
Observations of non-thermal emission from several supernova remnants suggest that magnetic fields close to the blast wave are much stronger than would be naively expected from simple shock compression of the field permeating the interstellar medium (ISM).
We present a simple model which is capable of achieving sufficient magnetic field amplification to explain the observations. We propose that the cosmic ray pressure gradient acting on the inhomogeneous ISM upstream of the supernova blast wave induces strong turbulence upstream of the supernova blast wave. The turbulence is generated through the differential acceleration of the upstream ISM which occurs as a result of density inhomogeneities in the ISM. This turbulence then amplifies the pre-existing magnetic field.
Numerical simulations are presented which demonstrate that amplification factors of 20 or more are easily achievable by this mechanism when reasonable parameters for the ISM and supernova blast wave are assumed. The length scale over which this amplification occurs is that of the diffusion length of the highest energy non-thermal particles.