TY - JOUR
T1 - X-Ray Diagnostics of Cassiopeia A’s “Green Monster”
T2 - Evidence for Dense Shocked Circumstellar Plasma
AU - Vink, Jacco
AU - Agarwal, Manan
AU - Slane, Patrick
AU - De Looze, Ilse
AU - Milisavljevic, Dan
AU - Patnaude, Daniel
AU - Temim, Tea
N1 - Publisher Copyright:
© 2024. The Author(s). Published by the American Astronomical Society.
PY - 2024/3/1
Y1 - 2024/3/1
N2 - The recent survey of the core-collapse supernova remnant Cassiopeia A (Cas A) with the MIRI instrument on board the James Webb Space Telescope (JWST) revealed a large structure in the interior region, referred to as the “Green Monster.” Although its location suggests that it is an ejecta structure, the infrared properties of the “Green Monster” hint at a circumstellar medium (CSM) origin. In this companion paper to the JWST Cas A paper, we investigate the filamentary X-ray structures associated with the “Green Monster” using Chandra X-ray Observatory data. We extracted spectra along the “Green Monster” as well as from shocked CSM regions. Both the extracted spectra and a principal component analysis show that the “Green Monster” emission properties are similar to those of the shocked CSM. The spectra are well fit by a model consisting of a combination of a nonequilibrium ionization model and a power-law component, modified by Galactic absorption. All the “Green Monster” spectra show a blueshift corresponding to a radial velocity of around −2300 km s−1, suggesting that the structure is on the near side of Cas A. The ionization age is around n e t ≈ 1.5 × 1011 cm−3 s. This translates into a preshock density of ∼12 cm−3, higher than previous estimates of the unshocked CSM. The relatively high n e t and relatively low radial velocity suggest that this structure has a relatively high density compared to other shocked CSM plasma. This analysis provides yet another piece of evidence that the CSM around Cas A’s progenitor was not that of a smooth steady wind profile.
AB - The recent survey of the core-collapse supernova remnant Cassiopeia A (Cas A) with the MIRI instrument on board the James Webb Space Telescope (JWST) revealed a large structure in the interior region, referred to as the “Green Monster.” Although its location suggests that it is an ejecta structure, the infrared properties of the “Green Monster” hint at a circumstellar medium (CSM) origin. In this companion paper to the JWST Cas A paper, we investigate the filamentary X-ray structures associated with the “Green Monster” using Chandra X-ray Observatory data. We extracted spectra along the “Green Monster” as well as from shocked CSM regions. Both the extracted spectra and a principal component analysis show that the “Green Monster” emission properties are similar to those of the shocked CSM. The spectra are well fit by a model consisting of a combination of a nonequilibrium ionization model and a power-law component, modified by Galactic absorption. All the “Green Monster” spectra show a blueshift corresponding to a radial velocity of around −2300 km s−1, suggesting that the structure is on the near side of Cas A. The ionization age is around n e t ≈ 1.5 × 1011 cm−3 s. This translates into a preshock density of ∼12 cm−3, higher than previous estimates of the unshocked CSM. The relatively high n e t and relatively low radial velocity suggest that this structure has a relatively high density compared to other shocked CSM plasma. This analysis provides yet another piece of evidence that the CSM around Cas A’s progenitor was not that of a smooth steady wind profile.
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U2 - 10.3847/2041-8213/ad2fc5
DO - 10.3847/2041-8213/ad2fc5
M3 - Article
AN - SCOPUS:85188006747
SN - 2041-8205
VL - 964
JO - Astrophysical Journal Letters
JF - Astrophysical Journal Letters
IS - 1
M1 - L11
ER -