Discovery of Stable Titanium at the Northeastern Jet of Cassiopeia A: Need for a Weak Jet Mechanism?

Abstract

The origin of the jet-like structures observed in Cassiopeia A is still unclear, although it seems to be related to its explosion mechanism. X-ray observations of the characteristic structures could provide us useful information on the explosive nucleosynthesis via the observation of elements, which is a unique approach to understand its origin. We here report the discovery of shocked stable Ti, which is produced only at the inner region of exploding stars, in the northeast jet of Cassiopeia A using the 1-Ms deep observation with the Chandra X-ray observatory. The observed Ti coexists with other intermediate-mass elements (e.g. Si, S, Ar, Ca) and Fe at the tip of the X-ray jet structure. We found that its elemental composition is well explained with the production by the incomplete Si burning regime, indicating that the formation process of the jet structure was sub-energetic at the explosion (the peak temperature during the nuclear burning must be < ∼ 5×10 9 K at most). Thus, we conclude that the energy source that formed the jet structure was not the primary engine for the supernova explosion. Our results are useful to limit the power of the jet-structure formation process, and a weak jet mechanism with low temperature may be needed to explain it.

X-ray Studies of the Inverted Ejecta Layers in the Southeast Area of Cassiopeia A

“…In the spectral analysis, the hydrogen column density was fixed to 1.2 × 10 22 cm −2 , which is a typical value for the southeast region ; Sato et al (2021); Ikeda et al (2022)), while kT e , n e t, and normalization and abundances of Ca, Ti, Cr, Mn, and Fe are treated as free parameters and the other abundances of elements are frozen to the solar values in Anders & Grevesse (1989). In region B, we found that the spectrum has significant contributions from pileup events due to the strong Si/S Heα emissions (see the broken lines in the bottom panels in Figure 5).…”

“…The observed Cr/Fe mass ratio can be used for determining the peak temperature during the Si burning regime (Yamaguchi et al 2017;Sato et al 2020aSato et al , 2021Ikeda et al 2022). Figure 7 shows the relation between the peak temperature during the nuclear burning and the Cr/Fe mass ratio in a 1D SN model used in Sato et al (2020bSato et al ( , 2021.…”

“…Here, the galactic supernova remnant Cassiopeia A (Cas A) is one of the most well-studied samples to discuss it. The highly asymmetric ejecta distributions of the remnant were observed in detail at multiple wavelengths (e.g., Fesen et al 2001Fesen et al , 2006Smith et al 2009;DeLaney et al 2010;Isensee et al 2010;Grefenstette et al 2014;Isensee et al 2012;DeLaney et al 2014;Alarie et al 2014;Patnaude & Fesen 2014;Milisavljevic & Fesen 2015;Fesen & Milisavljevic 2016;Grefenstette et al 2017;Ikeda et al 2022), which can be a unique tool to test the asymmetric effects by comparing them with theoretical calculations (e.g., Schure et al 2008;Wheeler et al 2008;Orlando et al 2016;Wongwathanarat et al 2017;Orlando et al 2021).…”