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Description
Young supernova remnants are ideal sites for studying the acceleration and transport of high-energy particles. This work presents a comprehensive investigation of particle acceleration in Cassiopeia A using spatially resolved X-ray observations, and explores how the surrounding circumstellar medium affects the acceleration efficiency. Radial intensity profiles of bright nonthermal X-ray filaments observed with Chandra are analyzed in regions dominated by synchrotron emission and significant polarization. The filament morphology is interpreted using a transport model that accounts for diffusive energy losses, superdiffusive propagation in the far upstream region, and magnetic field damping downstream of the shock. The local magnetic field strength and the characteristic diffusion length scales are derived. These parameters are compared with the level of magnetic turbulence inferred from X-ray polarization measurements. On larger scales, the role of the circumstellar medium shaped by the progenitor star in regulating shock evolution and maximum particle energies in Cassiopeia A is investigated. Shock evolution models suggest that Cassiopeia A may have been a PeVatron during its early expansion in a dense red supergiant wind, whereas the present shock propagates in a lower-density main-sequence wind. The analysis is extended to Tycho’s supernova remnant, a Type Ia explosion expanding into a uniform interstellar medium, showing distinctly different acceleration properties.
