The Density and Mass of Unshocked Ejecta in Cassiopeia A through Low Frequency Radio Absorption

Abstract

Characterizing the ejecta in young supernova remnants is a requisite step towards 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 arcseconds and 18.5 arcseconds resolution at 74 MHz. Together with higher frequency data we estimate an electron density of 4.2 electrons per cubic centimeters and a total mass of 0.39 Solar masses with uncertainties of a factor of about 2. This is a significant improvement over the 100 electrons per cubic centimeter 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.

arXiv comment18 pages, 12 figures, accepted to ApJ

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Cited by in corpus (40)

• Radio emission from Supernova Remnants
• The dust mass in Cassiopeia A from a spatially resolved Herschel analysis
• The distribution of radioactive ${}^{44}$Ti in Cassiopeia A
• Modeling SNR Cassiopeia A from the Supernova Explosion to its Current Age: The role of post-explosion anisotropies of ejecta
• The fully developed remnant of a neutrino-driven supernova: Evolution of ejecta structure and asymmetries in SNR Cassiopeia A
• Intermediate-Mass-Elements in Young Supernova Remnants Reveal Neutron Star Kicks by Asymmetric Explosions
• Interstellar and Ejecta Dust in the Cas A Supernova Remnant
• Subarcsecond international LOFAR radio images of the M82 nucleus at 118 MHz and 154 MHz
• Locating the most energetic electrons in Cassiopeia A
• Evidence for proton acceleration up to TeV energies based on VERITAS and Fermi-LAT observations of the Cas A SNR
• A JWST Survey of the Supernova Remnant Cassiopeia A
• Cassiopeia A, Cygnus A, Taurus A, and Virgo A at ultra-low radio frequencies
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• The mass, location and heating of the dust in the Cassiopeia A supernova remnant
• Progenitor Mass Distribution of Core-Collapse Supernova Remnants in Our Galaxy and Magellanic Clouds based on Elemental Abundances
• Element Abundances in the Unshocked Ejecta of Cassiopeia A
• Dust destruction and survival in the Cassiopeia A reverse shock
• A Sub-Solar Metallicity Progenitor for Cassiopeia A, the remnant of a Type IIb Supernova
• Thermal radio absorption as a tracer of the interaction of SNRs with their environments
• Low Radio Frequency Observations and Spectral Modelling of the Remnant of Supernova 1987A
• A Deep Near-Infrared [Fe II]+[Si I] Emission Line Image of the Supernova Remnant Cassiopeia A
• Dynamical Evolution and Radiative Processes of Supernova Remnants
• The Temperature and Ionization of Unshocked Ejecta in Cas A
• A Large Scale, Low Frequency Murchison Widefield Array Survey of Galactic HII regions between 260< l <\340
• Spatially Resolved Chandra Spectroscopy of the Large Magellanic Cloud Supernova Remnant N132D
• Mapping the spectral index of Cas A: evidence for flattening from radio to infrared
• Filamentary Ejecta Network in Cassiopeia~A Reveals Fingerprints of the Supernova Explosion Mechanism
• Free-free absorption parameters of Cassiopeia A from low-frequency interferometric observations
• Hints of a second explosion (a quark nova) in Cassiopeia A Supernova
• X-ray Studies of the Inverted Ejecta Layers in the Southeast Area of Cassiopeia A
• ATCA Study of Small Magellanic Cloud Supernova Remnant 1E 0102.2-7219
• The X-ray synchrotron rims in Cassiopeia A narrow with energy
• Characterising the Apertif primary beam response
• A High Resolution Study of Carbon Radio Recombination Lines towards Cassiopeia A
• XRISM Observations of Cassiopeia A: Overview, Atomic Data, and Spectral Models
• Multi-antenna probing of absorbing regions inside and outside Cassiopeia A
• Production of heavy $\alpha$-elements and ${}^{44}$Ti in Cas A: comparison to abundances from 1D core-collapse supernova models and evidence for Carbon-Oxygen shell mergers
• A Study of Radio Knots within Supernova Remnant Cassiopeia A
• An Asymmetrical Model for High Energy Radiation of Cassiopeia A
• Decadal brightening in the northeastern non-thermal filament of Cassiopeia A