Speaker
Description
Cassiopeia A (Cas A), the youngest known core-collapse supernova remnant (SNR) in the Milky Way, offers an unparalleled view of the explosions of massive stars. A >350 ks observation with XRISM has delivered an unprecedented high–spectral-resolution X-ray view of this archetypal remnant and produced the mission’s most productive dataset to date, with 5+ published papers. In this talk, I will present these latest XRISM results.
Key breakthroughs include the first X-ray detections of the odd-Z elements P, Cl, and K in any SNR. We uncover an incomplete ejecta shell in which Si- and S-rich components exhibit distinct ionization states and velocity structures. Near the projected center, we detect narrow, low-velocity emission lines likely associated with circumstellar material.
Using the new Bayesian spectral tool UltraSPEX, we present the first comprehensive microcalorimeter-based plasma mapping of an SNR. We identify clear kinematic differences between intermediate-mass (IMEs) and iron-group elements (IGEs), and a strong anti-correlation between ionization timescale and electron temperature, consistent with significant ejecta clumping (overdensities of ~10 for IGEs and up to ~100 for IMEs) and reduced historical reverse-shock velocities. Finally, we disentangle thermal and non-thermal components, showing that synchrotron emission contributes at least 47% of the 4–6 keV flux at XRISM resolution.
These results provide the most detailed spectroscopic portrait of Cas A to date.
| Talk category | NOVA Network 3 |
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