http://arxiv.org/abs/1905.04475
We report 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 from 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 nearly freely-expanding after $\sim$ 400 years since the explosion. The fastest moving knots showed proper motions up to $\sim$ 0.2 arcseconds per year. Based on our radial velocity measurements, we estimate a distance to Kepler’s SNR, $d$ $\sim$ 4.8 to 8.2 kpc. We find that the ejecta knots in our sample have an average space velocity of $\mid v_{s}\mid \sim$ 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 2 with a blueshifted spectrum, suggesting an asymmetry in the ejecta distribution in Kepler’s SNR along the line of sight.
M. Millard, J. Bhalerao, S. Park, et. al.
Tue, 14 May 19
48/91
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