We have analyzed XMM-Newton , Chandra , and Suzaku observations of Kepler ’ s supernova remnant ( SNR ) to investigate the properties of both the SN ejecta and the circumstellar medium ( CSM ) .
For comparison , we have also analyzed two similarly-aged , ejecta-dominated SNRs : Tycho ’ s SNR , thought to be the remnant of a typical Type Ia SN , and SNR 0509-67.5 in the Large Magellanic Cloud , thought to be the remnant of an overluminous ( SN1991T-like ) Type Ia SN .
By simply comparing the X-ray spectra , we find that line intensity ratios of iron-group elements ( IGE ) to intermediate-mass elements ( IME ) for Kepler ’ s SNR and SNR 0509-67.5 are much higher than those for Tycho ’ s SNR .
We therefore argue that Kepler is the product of an overlumious Type Ia SN .
This inference is supported by our spectral modeling , which reveals the IGE and IME masses respectively to be 0.95 ^ { +0.34 } _ { -0.37 } M _ { \odot } and 0.12 ^ { +0.19 } _ { -0.05 } M _ { \odot } ( Kepler ’ s SNR ) , 0.75 ^ { +0.51 } _ { -0.15 } M _ { \odot } and 0.34 ^ { +0.08 } _ { -0.25 } M _ { \odot } ( SNR 0509-67.5 ) , and 0.35 ^ { +0.55 } _ { -0.15 } M _ { \odot } and 0.70 ^ { +0.12 } _ { -0.28 } M _ { \odot } ( Tycho ’ s SNR ) .
We find that the CSM component in Kepler ’ s SNR consists of tenuous diffuse gas ( \sim 0.3 M _ { \odot } ) present throughout the entire remnant , plus dense knots ( \sim 0.035 M _ { \odot } ) .
Both of these components have an elevated N abundance ( N/H \sim 4 times the solar value ) , suggesting that they originate from CNO-processed material from the progenitor system .
The mass of the diffuse CSM allows us to infer the pre-SN mass-loss rate of the system to be \sim 1.5 \times 10 ^ { -5 } ( v _ { \mathrm { w } } /10 km s ^ { -1 } ) M _ { \odot } yr ^ { -1 } , in general agreement with results from recent hydrodynamical simulations .
The dense knots have slow optical proper motions as well as relatively small X-ray–measured ionization timescales , which indicates that they were located a few pc away from the progenitor system and were only recently heated by forward shocks .
Therefore , we argue that Kepler ’ s SN was an overluminous ( 91T-like ) event that started to interact with massive CSM a few hundred years after the explosion .
This supports the possible link between 91T-like SNe and the so-called “ Ia-CSM ” SNe — a rare class of SNe Ia associated with massive CSM .
The link implies that \sim 10 % of SNe Ia are associated with massive CSM which most likely originates from a companion star in a single degenerate progenitor system .