Article Summary #9

Measuring the Cosmic-Ray Acceleration Efficiency of a Supernova Remnant

E. A. Helder, J. Vink, C. G. Bassa, A. Bamba, et al. 2009, Science, 325, 719
http://www.sciencemag.org/cgi/content/abstract/325/5941/719

A widely studied topic both by astronomers and physicist today is Cosmic Rays, which are highly energetic particles that originate outside the Earth, travel through the universe, and hit our atmosphere. A known sub-category is that of accelerated cosmic rays and the accelerating process behind it is know to be mostly due to supernova remnants (SNR – expanding plasma shells caused by strong and violent exploding stars into supernovae and its boundary is called a “shock wave”) . This paper discusses one scenario of how a supernova remnant can accelerate the cosmic rays.

It has been found that for the known cosmic ray density to be stable in the Milky Way, every century three supernovae transform a tenth of their kinetic energy in cosmic ray energy. Supernova remnants lose a high amount of energy to the acceleration (i.e. kinetic energy) of the cosmic rays and this changes its kinematics. There are two known proofs of these energy loses: 1) a higher compression factor of the post-shock plasma, 2) a lower post-shock temperature.

The supernova remnant they look at is RCW 86 and for this source the radiation from the ultrarelativistic electrons is what causes the X-ray emission that they analyze. They find that behind this supernova remnant’s northeast shock, the cosmic ray induced pressure is higher than the thermal pressure. This implies that the temperature of the protons in the post-shock is different from the theoretically (i.e. standard) shock heating. This implies that cosmic rays are what produce more than half of the post-shock pressure.