A Super-Solar Metallicity for the Progenitor of Kepler's Supernova

TL;DR

Deep X-ray observations of Kepler's supernova remnant reveal super-solar metallicity and detailed elemental abundances, providing insights into the progenitor's nature and explosion mechanism of this Type Ia supernova.

Contribution

First detection of Mn, Cr, Ni, and Fe lines in Kepler's supernova remnant, indicating a super-solar metallicity progenitor and constraining explosion models.

Findings

Mn-to-Cr mass ratio ~0.77 suggests large neutron excess

Ni-to-Fe ratio consistent with explosive Si-burning

Progenitor metallicity estimated at ~3 Z_sun

Abstract

We have performed deep X-ray observations of the remnant of Kepler's supernova (SN 1604) as a Key Project of the Suzaku Observatory. Our main goal is to detect secondary Fe-peak elements in the SN ejecta to gain insights into the Type Ia supernova explosion mechanism and the nature of the progenitor. Here we report our initial results. We made a conclusive detection of X-ray emission lines from highly ionized Mn, Cr, and Ni as well as Fe. The observed Mn-to-Cr line flux ratio is ~0.60, ~30% larger than that measured in Tycho's remnant. We estimate a Mn-to-Cr mass ratio of ~0.77, which is strongly suggestive of a large neutron excess in the progenitor star before the onset of the thermonuclear runaway. The observed Ni-to-Fe line flux ratio (~0.03) corresponds to a mass ratio of ~0.06, which is generally consistent with the products of explosive Si-burning regime in Type Ia explosion models, and rules out contamination from the products of neutron-rich nuclear statistical equilibrium in the shocked ejecta. Together with the previously suggested luminous nature of the explosion, these mass ratios provide strong evidence for a super-solar metallicity in the SN progenitor (~3 Z_sun). Kepler's supernova was likely the thermonuclear explosion of a white dwarf formed in the recent past that must have exploded through a relatively prompt channel.