Towards Understanding Diffusive Shock Acceleration
Astronomy and astrophysics
Friday 05 September 2014
to 11:30 at
Andrey Beresnyak (Los Alamos National Lab)
Acceleration of cosmic rays (CRs) in supernova remnants (SNR) is
probably the best known case of shock acceleration. Observations
strongly suggest that SNR produce CRs with energies up to 10^15 eV or
higher. Thin X-ray rims observed in remnants and short timescale
variability points to magnetic field amplification near the shock. In
fact, simple estimates show that without field amplification in front
of the shock CR production will be negligible.
At the same time, the only agent acting in front of the shock are CR
themselves. Three approaches has been explored as possible sources of
CR-generated turbulence in front of the shock: streaming instability,
Bell's instability and the baroclinic term from cosmic ray pressure.
While models are being developed, new observations of very short
timescale variability appear to strain these models close to breaking
point. I will point to several ways to explain rapid variability.