G. E. Allen (MIT), M. D. Stage (UMass), J. C. Houck (MIT) and J. E. Davis
(MIT)We present the results of spectroscopic analyses of 1.1 megaseconds of
Chandra ACIS X-ray data for the supernova remnant Cas A. The analyses were
performed by extracting spectra from 1\"x1\" to 7\"x7\" overlapping boxes
at each point on a rectangular grid with 1\" spacing. Each set of spectra
and spatially-dependent responses was fitted with a simple thermal
model. The results of this analysis suggest that some, if not all, of the
regions in which the X-ray synchrotron emission is produced can be
identified. These regions have relatively high fitted electron temperatures
and relatively low elemental abundances. The regions whose X-ray emission
is dominated by synchrotron radiation seem be distributed around the
forward shock, except, perhaps, for portions of the southwestern face of
the remnant. The data for these regions were subsequently fitted with a
synchrotron emission model. The fitted critical frequencies associated
with the highest-energy electrons vary from about 10^16-10^18 Hz. This
variation indicates that the cut-off energy of the electron spectrum varies
by as much as one order of magnitude and/or the magnetic field strength
varies by as much as two orders of magnitude. In the regions with the
highest critical frequencies, the electrons must be accelerated about as
fast as possible (i.e. have diffusion coefficients comparable to the Bohm
coefficient).
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