How are particles accelerated to extreme energies producing shocks, jets and cosmic rays?

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Most young remnants (Cas A, Tycho, Kepler, SN1006) show clear signs of shock acceleration of electrons in the form of geometrically thin, spectrally featureless rims associated with their high-speed shock fronts. Evidence for the acceleration of cosmic-ray protons has been more difficult to obtain. Understanding how shocks accelerate and heat electrons and ions will require observations of young remnants, synchrotron-dominated ones, and older SNRs, such as the Cygnus Loop, that do not show strong non thermal X-ray emission from their shock fronts. To this end, IXO´s polarimetric and spectroscopic observations will be crucial.

Polarized X-rays are also expected from the shock waves produced by supernovae. These regions have long been thought to be sites for acceleration of cosmic rays and also to have magnetic fields. Many supernova remnants show hard X-ray spectra that indicate synchrotron emission by TeV electrons.The radiation from these electrons will be polarized. IXO will measure the strength and direction of the polarization as a probe of the magnetic field structure and particle distribution in the supernova shocks.

IXO will allow measurements of separate temperatures for electrons and for different ions, as well as Doppler widths and shifts. From these we will quantify the extent of electron heating; constrain non-Maxwellian components of the electron distribution (the lowest-energy cosmic rays); and identify the fraction of shock energy going to accelerated particles in remnants.

Selected References

A.M.Bykov, Yu.A.Uvarov, J.B.G.M.Bloemen, J.W. den Herder, J.S.Kaastra, "A Model of Polarized X-ray Emission from Twinkling Synchrotron Supernova Shells", MNRAS (in press), 2009. Download PDF

For more information, refer to IXO Astro 2010 Decadal White Papers: Starburst Galaxies: Outflows of Metals and Energy into the IGM, D. Strickland et al.