Direct Ejecta Velocity Measurements of Tycho's Supernova Remnant
  We present the first direct ejecta velocity measurements of Tycho's supernova remnant (SNR). Chandra's high angular resolution images reveal a patchy structure of radial velocities in the ejecta that can be separated into distinct redshifted, blueshifted, and low velocity ejecta clumps or blobs. The typical velocities of the redshifted and blueshifted blobs are <~ 7,800 km/s and <~ 5,000 km/s, respectively. The highest velocity blobs are located near the center, while the low velocity ones appear near the edge as expected for a generally spherical expansion. Systematic uncertainty on the velocity measurements from gain calibration was assessed by carrying out joint fits of individual blobs with both the ACIS-I and ACIS-S detectors. We determine the three-dimensional kinematics of the Si- and Fe-rich clumps in the southeastern quadrant and show that these knots form a distinct, compact, and kinematically-connected structure, possibly even a chain of knots strung along the remnant's edge. By examining the viewing geometries we conclude that the knots in the southeastern region are unlikely to be responsible for the high velocity Ca II absorption features seen in the light echo spectrum of SN 1572, the originating event for Tycho's SNR. 
Toshiki Sato (1, 2, 3) and John P. Hughes (3) ((1) Tokyo Metropolitan   University, (2) ISAS/JAXA, (3) Rutgers University)
astro-ph.HE