A Deep Chandra Observation of Kepler's Supernova Remnant: An Anomalous Type Ia Supernova
Stephen Reynolds (North Carolina State University) , K.J. Borkowski (NC State U), J.M. Blondin (NC State U), C. Badenes (Rutgers), J.P. Hughes (Rutgers), U. Hwang (NASA/GSFC), J.M. Laming (NRL)
We present results from our 750 ks Chandra Large Project observation of the remnant of Kepler's supernova of 1604. This spectacular dataset, containing about 30 million counts, allows detailed spectroscopy on arcsecond scales. We have examined the spectra of over 100 small regions, and find that the vast bulk of emission from Kepler can be identified with iron and silicon-rich ejecta. Very few regions show abundances closer to solar, but those are spatially associated with N-rich optical knots, and show some evidence for N enhancement in X-rays as well. Those regions are also the only locations where O is noticeable in the spectra. A few regions are dominated by synchrotron emission, in the form of knots and diffuse patches as well as thin filaments. There are no O-rich regions. We are forced to conclude that Kepler is the remnant of a thermonuclear supernova, although evidence is also strong that the ambient medium into which the blast wave is expanding is circumstellar material lost from the progenitor. Thus Kepler may be an example of a thermonuclear supernova from a more massive progenitor system, perhaps to be identified with "prompt" Type Ia supernovae required to explain the correlation of Type Ia supernova rates with galaxy star formation rates. However, Kepler's kinematics are also unusual and may require a whole new Ia mechanism, such as the thermonuclear explosion of a single star. The implications of different explosion mechanisms for the cosmological use of SNe Ia are considerable. I shall discuss the significance of our observation for shock-acceleration physics and for the nature of the Type Ia phenomenon.