The 3D Distribution of 44-Ti in Cassiopeia A

The mechanisms behind core-collapse supernovae represent one of the most important unsolved problems in stellar astrophysics and are of interest to many branches of physics and astronomy, such as nucleosynthesis, pulsar formation, gamma-ray bursts, and gravitational wave production. Few direct observational constraints exist that probe fundamental parameters such as the explosion asymmetries and dynamics. One of the most direct probes of the physics of the core-collapse supernova engine is ⁴⁴Ti, which is producing near the "mass cut" in the collapsing star with material interior to the ⁴⁴Ti accreting onto the nascent compact object the the ⁴⁴Ti mostly ejected during the explosion.Here we present the results from the full NuSTAR observational campaign (over 2 Ms) of the famous Type II supernova remnant Cassiopeia A (Cas A). NuSTAR is the first X-ray observatory capable of focusing the X-rays that are emitted during the radioactive decay of ⁴⁴Ti to ⁴⁴Ca. For a supernova remnant like Cas A, which is both young and nearby, we can to image the distribution of the ⁴⁴Ti ejecta. Early results (using the first 1 Ms of data) produced the first 2D maps of the ⁴⁴Ti in Cas A, revealing the asymmetry in the ⁴⁴Ti ejecta and the striking discrepancy between the distributions of ⁴⁴Ti and the ionized Fe emission seen by Chandra. With the additional exposure time we can perform spatially-resolved spectroscopy to determine the Doppler shift of the ⁴⁴Ti-emitting regions, giving us the ability to construct a 3D representation of the remnant. We can compare this to the excellent data from Chandra and Spitzer which have been used to perform similar studies of the ionized X-ray ejecta and IR emitting ejecta, respectively. We find an increasingly complex picture of the remnant, with ⁴⁴Ti appearing wtih Fe in some regions on the remnant and other regions of Fe that are apparently ⁴⁴Ti free. We will discuss our findings, and the implications of these results.