For the first time, astronomers have mapped the rate of acceleration of cosmic ray electrons in a supernova remnant. The new map shows that the electrons are being accelerated at close to the theoretically maximum rate. This discovery provides compelling evidence that supernova remnants are key sites for energizing charged particles.
"The electrons pick up speed each time they bounce across the shock front, like they're in a relativistic pinball machine," said team member Glenn Allen of the Massachusetts Institute of Technology (MIT), Cambridge. "The magnetic fields are like the bumpers, and the shock is like a flipper."
In their analysis of the huge data set, the team was able to separate the X-rays coming from the accelerating electrons from those coming from the heated stellar debris. The data imply that some of these electrons are accelerated at a rate close to the maximum predicted by theory. Cosmic rays are composed of electrons, protons, and ions, of which only glow from electrons is detectable in X-rays. Protons and ions, which constitute the bulk of cosmic rays, are expected to behave similarly to the electrons.
"It's exciting to see regions where the glow produced by cosmic rays actually outshines the 10-million-degree gas heated by the supernova's shock waves," said John Houck, also of MIT. "This helps us understand not only how cosmic rays are accelerated, but also how supernova remnants evolve."
As the total energy of the cosmic rays behind the shock wave increases, the magnetic field behind the shock is modified, along with the character of the shock wave itself. Researching the conditions in the shocks helps astronomers trace the changes of the supernova remnant with time, and ultimately better understand the original supernova explosion.
NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the agency's Science Mission Directorate. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center, Cambridge, Mass.
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