0 Electron Heating and Cosmic Rays at a Supernova Shock from Chandra X - ray Observations of E 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 post-shock electron temperature and proper motion of a young SNR, specifically to address questions about the post-shock partition of energy among electrons, ions, and cosmic rays. The expansion rate, 0.100% ± 0.025%yr, and inferred age, ∼1000 yr, of E0102.2−7219, from a comparison of X-ray observations spanning 20 years, 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 and a range of electron temperatures 2.5 45 keV, dependent on the degree of collisionless electron heating. Analysis of the Chandra ACIS spectrum of the immediate post-shock 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 only be reconciled if we assume that a significant fraction of the shock energy, rather than contributing to the heating of the post-shock electrons and ions, has gone into generating cosmic rays. Subject headings: cosmic rays — ISM: individual (E0102.2−7219) — shock waves – supernova remnants — X-rays: ISM