X-ray observations of supernova remnants ( SNRs ) allow us to investigate the chemical inhomogeneity of ejecta , offering unique insight into the nucleosynthesis in supernova explosions .
Here we present detailed imaging and spectroscopic studies of the “ Fe knot ” located along the eastern rim of the Type Ia SNR Tycho ( SN 1572 ) using Suzaku and Chandra long-exposure data .
Surprisingly , the Suzaku spectrum of this knot shows no emission from Cr , Mn , or Ni , which is unusual for the Fe-rich regions in this SNR .
Within the framework of the canonical delayed-detonation models for SN Ia , the observed mass ratios M _ { Cr } / M _ { Fe } < 0.023 , M _ { Mn } / M _ { Fe } < 0.012 , and M _ { Ni } / M _ { Fe } < 0.029 ( at 90 % confidence ) can only be achieved for a peak temperature of ( 5.3–5.7 ) \times 10 ^ { 9 } K and a neutron excess of \lesssim 2.0 \times 10 ^ { -3 } .
These constraints rule out the deep , dense core of a Chandrasekhar-mass white dwarf as the origin of the Fe knot , and favors either incomplete Si burning or the \alpha -rich freeze-out regime , probably close to their boundary .
An explosive He burning regime is a possible alternative , although this hypothesis is in conflict with the main properties of this SNR .