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Synchrotron X-ray Emission from Galactic Supernova Remnants and Cosmic-Ray Acceleration

For the large majority of galactic supernova remnants (SNRs), the X-ray emission detected from these sources originates from a hot gas that has been abruptly shock heated to several million degrees. This gassynchrotron.jpg proceeds to cool by emitting high energy light (X-ray photons). However, in the cases of several SNRs, a prominent "non-thermal" component is seen in the X-ray spectra of these sources. While the thermal X-ray emission from SNRs manifests itself with prominent spectral emission lines, the spectrum of non-thermal X-ray emission is remarkably featureless and is instead just a continuum of radiation. The origin of this observed non-thermal X-ray emission at least in some cases is believed to be cosmic-ray electrons that have been accelerated to very nearly the speed of light that gyrate in the enhanced magnetic fields associated with SNRs. Cosmic-rays are particles that rain steadily down on the Earth from deep space: these particles appear to reach very high energies and scientists are still investigating just how these particles can be accelerated to such exceptional velocities.

Astronomical sources like SNRs are nature's particle accelerators and can accelerate particles to energies that exceed greatly those attained by particle accelerators built by humans! Pannuti and his students analyze radio and X-ray observations of galactic SNRs that feature non-thermal X-ray emission in their spectra and investigate both the physical conditions of SNRs that are conducive to acceleration and the maximum energies to which SNRs can accelerate cosmic-ray electrons.