Spitzer IRAC images and sample spectra of Cassiopeia A's explosion

Ennis, Jessica A., Rudnick, Lawrence, Reach, William T., Smith, J. D., Rho, Jeonghee, DeLaney, Tracey, Gomez, Haley Louise ORCID: https://orcid.org/0000-0003-3398-0052 and Kozasa, Takashi 2006. Spitzer IRAC images and sample spectra of Cassiopeia A's explosion. Astrophysical Journal 652 (1) , pp. 376-386. 10.1086/508142

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Abstract

We present Spitzer IRAC images and representative 5.27-38.5 μm IRS spectra of the Cas A SNR. We find that various IRAC channels are each most sensitive to a different spectral and physical component. Channel 1 (3.6 μm) provides an excellent match to the radio synchrotron images. Where channel 1 is strong with respect to the other IRAC channels, the longer wavelength spectra show a broad continuum gently peaking around 26 μm, with weak or no lines. We suggest that this is due to unenriched progenitor circumstellar dust behind the outer shock. Where channel 4 (8 μm) is relatively brightest, the long-wavelength spectra show a strong, 2-3 μm wide peak at 21 μm, likely due to silicates and protosilicates. Strong ionic lines of [Ar II], [Ar III], [S IV], and [Ne II] also appear in these regions. We suggest that in these locations, the dust and ionic emission originate from the explosion's O-burning layers. The regions where channels 2 (4.5 μm) and 3 (5.6 μm) are strongest relative to channel 4 show a spectrum that rises gradually to 38 μm, becoming flatter longward of 21 μm, along with higher ratios of [Ne II] to [Ar II]. We suggest that the dust and ionic emission in these locations arise primarily from the C- and Ne-burning layers. All of these findings are consistent with asymmetries deep in the explosion, producing variations in the velocity structure in different directions, but generally preserving the nucleosynthetic layering. At each location, the dust and ionic lines in the mid-infrared and the hotter and more highly ionized optical and X-ray emission are then dominated by the layer currently encountering the reverse shock in that direction.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Subjects:	Q Science > QB Astronomy
Publisher:	IOP Publishing
ISSN:	0004-637X
Last Modified:	24 Oct 2022 10:44
URI:	https://orca.cardiff.ac.uk/id/eprint/45712

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