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Astronomy Colloquium
"Magnetic Fields in the Cosmic-ray modified shocks"
Date: Tuesday, January 12th
Time: 3:30 pm
Place: 3425 Sterling Hall
Speaker: Andrey Beresynak, UW Madison Astronomy
Abstract: We propose a model for Diffusive Shock Acceleration (DSA) in which
stochastic magnetic fields in the shock precursor are generated
through purely fluid mechanisms of a so-called small-scale dynamo.
This contrasts with previous DSA models that considered magnetic
fields amplified through cosmic ray streaming instabilities; i.e.,
either by way of individual particles resonant scattering in the
magnetic fields, or by macroscopic electric currents associated with large-scale cosmic ray streaming. In our picture, the solenoidal velocity perturbations that amplify magnetic fields are produced through the interactions of the pressure gradient of the cosmic ray precursor and density inhomogeneities in the inflowing fluid.
Our estimates show that this mechanism provides fairly fast<br>
growth of magnetic field and is very generic. For supernovae shocks this mechanism is capable of generating upstream magnetic fields that are sufficiently strong for accelerating cosmic rays up to around $10^{16}$ eV.<br>
Host: UW Astronomy Dept
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