Electron Heating and Cosmic Rays at a Supernova Shock from [ITAL]Chandra[/ITAL] X-Ray Observations of 1E 0102.2−7219

In this Letter, we use the unprecedented spatial resolution of the Chandra X-Ray Observatory to carry out, for the first time, a measurement of the postshock electron temperature and proper motion of a young supernova remnant, specifically to address questions about the postshock partition of energy among electrons, ions, and cosmic rays. The expansion rate, 0.100% ± 0.025% yr -1 , and inferred age, ~1000 yr, of 1E 0102.2-7219, from a comparison of X-ray observations spanning 20 yr, are fully consistent with previous estimates based on studies of high-velocity oxygen-rich optical filaments in the remnant. With a radius of 6.4 pc for the blast wave estimated from the Chandra image, our expansion rate implies a blast-wave velocity of ~6000 km s -1 and a range of electron temperatures 2.5-45 keV, dependent on the degree of collisionless electron heating. Analysis of the Chandra CCD spectrum of the immediate postshock region reveals a thermal plasma with abundances and column density typical of the Small Magellanic Cloud and an electron temperature of 0.4-1 keV. The measured electron temperature is significantly lower than the plausible range above, which can be reconciled only if we assume that a significant fraction of the shock energy, rather than contributing to the heating of the postshock electrons and ions, has gone into generating cosmic rays.