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 ChandraX-ray Observatory to carry out, for the first time, a measurement of thepost-shock electron temperature and proper motion of a young SNR, specificallyto address questions about the post-shock partition of energy among electrons,ions, and cosmic rays. The expansion rate, 0.100 +/- 0.025 percent per yr, andinferred age, ~1000 yr, of E0102.2-7219, from a comparison of X-rayobservations spanning 20 years, are fully consistent with previous estimatesbased 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 ofelectron temperatures 2.5 - 45 keV, dependent on the degree of collisionlesselectron heating. Analysis of the Chandra ACIS spectrum of the immediatepost-shock region reveals a thermal plasma with abundances and column densitytypical of the Small Magellanic Cloud and an electron temperature of 0.4-1 keV.The measured electron temperature is significantly lower than the plausiblerange above, which can only be reconciled if we assume that a significantfraction of the shock energy, rather than contributing to the heating of thepost-shock electrons and ions, has gone into generating cosmic rays.Comment: 13 pages, including 2 postscript figs, LaTeX. Accepted by Ap