The theory of diffusive shock acceleration provides for several limitations to the maximum energy particles can reach in supernova-remnant shocks. Two limits result from the acceleration time being limited by the remnant age or by the timescale for synchrotron losses, while particles with gyroradii longer than wavelengths of any MHD waves present will not scatter and will escape freely. For remnants younger than about 5000 yr, the acceleration-time limits imply maximum electron energies of order 1012-1014eV, high enough to produce keV synchrotron radiation. The authors describe a modeling program to calculate X-ray images and spectra from supernova remnants. Spectra result from a superposition of emission from regions with different maximum energies, and curve gently through the X-ray bandpass, approximating power-laws. Most young remnants show obviously thermal emission which is then an upper limit on a possible nonthermal component. Hard components sometimes seen in SNR X-ray spectra could be due to the synchrotron process. X-ray-emitting electrons will have long diffusion lengths ahead of the shock and should produce a synchrotron "halo" outside the main shock, which may be detectable. Detections or limits on these evidences of non-thermal X-rays provide surprisingly strong constraints on the microphysical properties of electron scattering and diffusion, and on the external magnetic-field strength.
Roentgenstrahlung from the Universe
- Pub Date:
- February 1996
- Supernova Remnants: Synchrotron Radiation;
- Supernova Remnants: X Rays;
- Supernova Remnants: Magnetohydrodynamics