Measuring Ejecta Velocities in Tycho's and Kepler's Supernova Remnants with the Chandra HETGS
Abstract
We report measurements of the bulk radial velocity from a sample of small, X-ray emitting metal-rich ejecta knots in Kepler's and Tycho's supernova remnants (SNRs). We measure the Doppler shift of the Si K line center energy in the spectra of these knots from our Chandra High-Energy Transmission Grating Spectrometer (HETGS) observations to estimate their radial velocities. Our preliminary results on the analysis of Tycho's SNR show radial velocities up to v_r ~ 5,000 km/s in several ejecta knots. In Kepler's SNR, we estimate high radial velocities of up to v_r ~ 9,000 km/s. We also measure proper motions for these ejecta knots based on the archival Advanced CCD Imaging Spectrometer (ACIS) data of Kepler's SNR taken in 2000, 2004, 2006, and 2014. The fastest moving knots showed proper motions of up to ~ 0.2 arcseconds per year. A few knots with the highest radial velocities also exhibit large proper motions, indicating that they are nearly freely expanding. Assuming that these high velocity ejecta knots are freely expanding near or beyond the main SNR shell, we estimate a distance to Kepler of d ~ 5 to 8.5 kpc. The ejecta knots in our sample have an average space velocity of | v_s| ~ 5,000 km/s (at a distance of 6 kpc) in Kepler's SNR. Eleven out of these 15 ejecta knots from our sample show a redshifted spectrum, suggesting an asymmetry in the ejecta distribution in Kepler's SNR along the line of sight. This work has been supported in part by NASA Chandra Grants GO6-17060X, GO7-18061X, and AR7-18006X.
- Publication:
-
Supernova Remnants: An Odyssey in Space after Stellar Death II
- Pub Date:
- June 2019
- Bibcode:
- 2019sros.confE.199M