Estimating the rates of electron acceleration in SNR shocks using 
Chandra

Michael Stage (UMass-Amherst)

Over the last six years, the Advanced CCD Imaging Spectrometer (ACIS)
on Chandra has captured the highest resolution X-ray images of several
supernova remnants, the most spectacular example the Cassiopeia A
megasecond observation from cycle 5. The observations of thermally
dominated, young supernova remnants such as Cassiopeia A, Kepler, and
Tycho show complex morphology often featuring narrow, filamentary,
continuum dominated emission at the outer shocks. Young supernova
remnants are believed to be possibly a source of and the main
accelerator of Galactic cosmic rays. The emission from the filaments
is believed to be synchrotron radiation associated with the
acceleration of cosmic-ray electrons to TeV energies, rather than
thermal bremsstrahulung associated with the ejecta emission. Using a
combination of CIAO tools and a suite of specialized software
utilizing the S-Lang scripting capabilities of ISIS, we have been able
to analyze these extended sources using the full spatial and spectral
information available from the ACIS data. Specifically, for Cas A, we
have been able to identify, isolate, extract, and fit the spectra of
the emission at each of about ten thousand locations along the
filaments with a synchrotron model. We present maps at 1 arcsecond
scale of the critical frequency associated with the exponential
cut-off of the synchrotron spectrum as well as of the ratio of the
electron diffusion coefficient to the Bohm coefficient, calculated
from the critical frequency and shock velocity. At several locations,
our maps indicate diffusion rates comparable to the Bohm limit-that
is, that electrons are being accelerated about as fast as possible.