We report our measurements of the bulk radial velocity from a sample of small , metal-rich ejecta knots in Kepler ’ s Supernova Remnant ( SNR ) .
We measure the Doppler shift of the He-like Si K \alpha line center energy in the spectra of these knots based on our Chandra High-Energy Transmission Grating Spectrometer ( HETGS ) observation to estimate their radial velocities .
We estimate high radial velocities of up to \sim 8,000 km s -1 for some of these ejecta knots .
We also measure proper motions for our sample based on the archival Chandra Advanced CCD Imaging Spectrometer ( ACIS ) data taken in 2000 , 2006 , and 2014 .
Our measured radial velocities and proper motions indicate that some of these ejecta knots are almost freely-expanding after \sim 400 years since the explosion .
The fastest moving knots show proper motions up to \sim 0.2 arcseconds per year .
Assuming that these high velocity ejecta knots are traveling ahead of the forward shock of the SNR , we estimate the distance to Kepler ’ s SNR d \sim 4.4 to 7.5 kpc .
We find that the ejecta knots in our sample have an average space velocity of v \textsubscript { s } \sim 4,600 km s -1 ( at a distance of 6 kpc ) .
We note that 8 out of the 15 ejecta knots from our sample show a statistically significant ( at the 90 % confidence level ) redshifted spectrum , compared to only two with a blueshifted spectrum .
This may suggest an asymmetry in the ejecta distribution in Kepler ’ s SNR along the line of sight , however a larger sample size is required to confirm this result .