<i>SPITZER</i>SPECTRAL MAPPING OF SUPERNOVA REMNANT CASSIOPEIA A

Smith, J. D.; Rudnick, Lawrence; DeLaney, Tracey; Rho, Jeonghee; Gomez, Haley Louise; Kozasa, Takashi; Reach, W. T.; Isensee, Karl

doi:10.1088/0004-637x/693/1/713

Cited by 76 publications

(137 citation statements)

References 37 publications

(69 reference statements)

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“…This is the same absorption morphology noted by Kassim et al (1995) et al 2006). The density and temperature conditions derived for this material based on the infrared line ratios confirms that it is indeed cold, low density, unshocked, photoionized ejecta (Smith et al 2009). In order to confirm the hypothesis of Kassim et al (1995) that the low frequency free-free absorption seen in Cas A is due to unshocked ejecta, we compare the Δα image to the infrared [Si ii] image.…”

Section: Spectral Index Difference (δα)supporting

confidence: 56%

“…We now know based on the Spitzer data that the ejecta are organized into a "thick disk" structure, tilted at ∼70 • from the line-of-sight, providing further evidence that the explosion, or subsequent evolution of the SNR prior to the reverse shock encounter, must have been asymmetric. An upper limit of 100 cm −1 was determined for the electron density of the unshocked ejecta based on infrared [S iii] line ratios, but the actual density is likely much lower (Eriksen 2009;Smith et al 2009). …”

Section: [S Iii] [S Iv] and [Si Ii]mentioning

confidence: 99%

“…At the density we infer for the unshocked ejecta, [ (Smith et al 2009). As explained in Section 6.2, the Fe discrepancy in Cas A may be resolved if the bulk of the Fe ejecta have already passed through the reverse shock and the remaining interior Fe is of lower density than the unshocked Si-and O-rich ejecta.…”

Section: Comparison To Sn1006mentioning

confidence: 99%

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The Density and Mass of Unshocked Ejecta in Cassiopeia a Through Low Frequency Radio Absorption

DeLaney

Kassim

Rudnick

et al. 2014

ApJ

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Characterizing the ejecta in young supernova remnants is a requisite step toward a better understanding of stellar evolution. In Cassiopeia A the density and total mass remaining in the unshocked ejecta are important parameters for modeling its explosion and subsequent evolution. Low frequency (<100 MHz) radio observations of sufficient angular resolution offer a unique probe of unshocked ejecta revealed via free-free absorption against the synchrotron emitting shell. We have used the Very Large Array plus Pie Town Link extension to probe this cool, ionized absorber at 9 and 18. 5 resolution at 74 MHz. Together with higher frequency data we estimate an electron density of 4.2 cm −3 and a total mass of 0.39 M with uncertainties of a factor of ∼2. This is a significant improvement over the 100 cm −3 upper limit offered by infrared [S iii] line ratios from the Spitzer Space Telescope. Our estimates are sensitive to a number of factors including temperature and geometry. However using reasonable values for each, our unshocked mass estimate agrees with predictions from dynamical models. We also consider the presence, or absence, of cold iron-and carbon-rich ejecta and how these affect our calculations. Finally we reconcile the intrinsic absorption from unshocked ejecta with the turnover in Cas A's integrated spectrum documented decades ago at much lower frequencies. These and other recent observations below 100 MHz confirm that spatially resolved thermal absorption, when extended to lower frequencies and higher resolution, will offer a powerful new tool for low frequency astrophysics.

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Section: Spectral Index Difference (δα)supporting

confidence: 56%

Section: [S Iii] [S Iv] and [Si Ii]mentioning

confidence: 99%

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The Density and Mass of Unshocked Ejecta in Cassiopeia a Through Low Frequency Radio Absorption

DeLaney

Kassim

Rudnick

et al. 2014

ApJ

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“…The lines identified are typical of those seen in other supernova remnants (Arendt et al 1999;Oliva et al 1999;Temim et al 2006;Neufeld et al 2007;Smith et al 2009;Andersen et al 2011;Ghavamian et al 2012;Sankrit et al 2014). The accuracy of the measurement of the line strengths is limited by the modest S/N of some lines, and the presence of strong (sometimes dominant) and structured background emission from the ISM in some of the lines.…”

Section: Emission Line (Gas) Evolutionmentioning

confidence: 82%

Infrared Continuum and Line Evolution of the Equatorial Ring Around Sn 1987a

Arendt

Dwek

Bouchet

et al. 2016

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Spitzer observations of SN 1987A have now spanned more than a decade. Since day ∼4000, mid-infrared (mid-IR) emission has been dominated by that from shock-heated dust in the equatorial ring (ER). From 6000 to 8000 days after the explosion, Spitzer observations included broadband photometry at 3.6-24 μm, and low and moderate resolution spectroscopy at 5-35 μm. Here we present later Spitzer observations, through day 10,377, which include only the broadband measurements at 3.6 and 4.5 μm. These data show that the 3.6 and 4.5 μm brightness has clearly begun to fade after day ∼8500, and no longer tracks the X-ray emission as well as it did at earlier epochs. This can be explained by the destruction of the dust in the ER on timescales shorter than the cooling time for the shocked gas. We find that the evolution of the late time IR emission is also similar to the now fading optical emission. We provide the complete record of the IR emission lines, as seen by Spitzer prior to day 8000. The past evolution of the gas as seen by the IR emission lines seems largely consistent with the optical emission, although the IR [Fe II] and [Si II] lines show different, peculiar velocity structures.

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“…This material was first discovered via free-free absorption at low radio frequencies (Kassim et al 1995) and has since been detected in the infrared (Rho et al 2008; Smith et al 2009). This material was demonstrated to be in substantially different physical conditions than recently shocked material on the Bright Ring through a combination of Doppler analysis and line ratio measurements (Smith et al 2009).…”

Section: Introductionmentioning

confidence: 99%

The Three-Dimensional Structure of Interior Ejecta in Cassiopeia a at High Spectral Resolution

Isensee

Rudnick

DeLaney

et al. 2010

ApJ

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We used the Spitzer Space Telescope's Infrared Spectrograph to create a high-resolution spectral map of the central region of the Cassiopeia A (Cas A) supernova remnant, allowing us to make a Doppler reconstruction of its threedimensional structure. The ejecta responsible for this emission have not yet encountered the remnant's reverse shock or the circumstellar medium, making it an ideal laboratory for exploring the dynamics of the supernova explosion itself. We observe that the O, Si, and S ejecta can form both sheet-like structures and filaments. Si and O, which come from different nucleosynthetic layers of the star, are observed to be coincident in velocity space in some regions, and separated by 500 km s −1 or more in others. Ejecta traveling toward us are, on average, ∼900 km s −1 slower than the material traveling away from us. We compare our observations to recent supernova explosion models and find that no single model can simultaneously reproduce all the observed features. However, models of different supernova explosions can collectively produce the observed geometries and structures of the interior emission. We use the results from the models to address the conditions during the supernova explosion, concentrating on asymmetries in the shock structure. We also predict that the back surface of Cas A will begin brightening in ∼30 years, and the front surface in ∼100 years.

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SPITZERSPECTRAL MAPPING OF SUPERNOVA REMNANT CASSIOPEIA A

Cited by 76 publications

References 37 publications

The Density and Mass of Unshocked Ejecta in Cassiopeia a Through Low Frequency Radio Absorption

The Density and Mass of Unshocked Ejecta in Cassiopeia a Through Low Frequency Radio Absorption

Infrared Continuum and Line Evolution of the Equatorial Ring Around Sn 1987a

The Three-Dimensional Structure of Interior Ejecta in Cassiopeia a at High Spectral Resolution

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