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Title: THE IMPORTANCE OF PHYSICAL MODELS FOR DERIVING DUST MASSES AND GRAIN SIZE DISTRIBUTIONS IN SUPERNOVA EJECTA. I. RADIATIVELY HEATED DUST IN THE CRAB NEBULA

Abstract

Recent far-infrared (IR) observations of supernova remnants (SNRs) have revealed significantly large amounts of newly condensed dust in their ejecta, comparable to the total mass of available refractory elements. The dust masses derived from these observations assume that all the grains of a given species radiate at the same temperature, regardless of the dust heating mechanism or grain radius. In this paper, we derive the dust mass in the ejecta of the Crab Nebula, using a physical model for the heating and radiation from the dust. We adopt a power-law distribution of grain sizes and two different dust compositions (silicates and amorphous carbon), and calculate the heating rate of each dust grain by the radiation from the pulsar wind nebula. We find that the grains attain a continuous range of temperatures, depending on their size and composition. The total mass derived from the best-fit models to the observed IR spectrum is 0.019-0.13 M{sub Sun }, depending on the assumed grain composition. We find that the power-law size distribution of dust grains is characterized by a power-law index of 3.5-4.0 and a maximum grain size larger than 0.1 {mu}m. The grain sizes and composition are consistent with what is expected formore » dust grains formed in a Type IIP supernova (SN). Our derived dust mass is at least a factor of two less than the mass reported in previous studies of the Crab Nebula that assumed more simplified two-temperature models. These models also require a larger mass of refractory elements to be locked up in dust than was likely available in the ejecta. The results of this study show that a physical model resulting in a realistic distribution of dust temperatures can constrain the dust properties and affect the derived dust masses. Our study may also have important implications for deriving grain properties and mass estimates in other SNRs and for the ultimate question of whether SNe are major sources of dust in the Galactic interstellar medium and in external galaxies.« less

Authors:
;  [1]
  1. Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
Publication Date:
OSTI Identifier:
22133998
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 774; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CARBON; COSMIC DUST; CRAB NEBULA; DISTRIBUTION; GALAXIES; GRAIN SIZE; HEATING RATE; INFRARED SPECTRA; INTERSTELLAR GRAINS; MASS; PULSARS; REFRACTORIES; SILICATES; STELLAR WINDS

Citation Formats

Temim, Tea, and Dwek, Eli, E-mail: tea.temim@nasa.gov. THE IMPORTANCE OF PHYSICAL MODELS FOR DERIVING DUST MASSES AND GRAIN SIZE DISTRIBUTIONS IN SUPERNOVA EJECTA. I. RADIATIVELY HEATED DUST IN THE CRAB NEBULA. United States: N. p., 2013. Web. doi:10.1088/0004-637X/774/1/8.
Temim, Tea, & Dwek, Eli, E-mail: tea.temim@nasa.gov. THE IMPORTANCE OF PHYSICAL MODELS FOR DERIVING DUST MASSES AND GRAIN SIZE DISTRIBUTIONS IN SUPERNOVA EJECTA. I. RADIATIVELY HEATED DUST IN THE CRAB NEBULA. United States. doi:10.1088/0004-637X/774/1/8.
Temim, Tea, and Dwek, Eli, E-mail: tea.temim@nasa.gov. Sun . "THE IMPORTANCE OF PHYSICAL MODELS FOR DERIVING DUST MASSES AND GRAIN SIZE DISTRIBUTIONS IN SUPERNOVA EJECTA. I. RADIATIVELY HEATED DUST IN THE CRAB NEBULA". United States. doi:10.1088/0004-637X/774/1/8.
@article{osti_22133998,
title = {THE IMPORTANCE OF PHYSICAL MODELS FOR DERIVING DUST MASSES AND GRAIN SIZE DISTRIBUTIONS IN SUPERNOVA EJECTA. I. RADIATIVELY HEATED DUST IN THE CRAB NEBULA},
author = {Temim, Tea and Dwek, Eli, E-mail: tea.temim@nasa.gov},
abstractNote = {Recent far-infrared (IR) observations of supernova remnants (SNRs) have revealed significantly large amounts of newly condensed dust in their ejecta, comparable to the total mass of available refractory elements. The dust masses derived from these observations assume that all the grains of a given species radiate at the same temperature, regardless of the dust heating mechanism or grain radius. In this paper, we derive the dust mass in the ejecta of the Crab Nebula, using a physical model for the heating and radiation from the dust. We adopt a power-law distribution of grain sizes and two different dust compositions (silicates and amorphous carbon), and calculate the heating rate of each dust grain by the radiation from the pulsar wind nebula. We find that the grains attain a continuous range of temperatures, depending on their size and composition. The total mass derived from the best-fit models to the observed IR spectrum is 0.019-0.13 M{sub Sun }, depending on the assumed grain composition. We find that the power-law size distribution of dust grains is characterized by a power-law index of 3.5-4.0 and a maximum grain size larger than 0.1 {mu}m. The grain sizes and composition are consistent with what is expected for dust grains formed in a Type IIP supernova (SN). Our derived dust mass is at least a factor of two less than the mass reported in previous studies of the Crab Nebula that assumed more simplified two-temperature models. These models also require a larger mass of refractory elements to be locked up in dust than was likely available in the ejecta. The results of this study show that a physical model resulting in a realistic distribution of dust temperatures can constrain the dust properties and affect the derived dust masses. Our study may also have important implications for deriving grain properties and mass estimates in other SNRs and for the ultimate question of whether SNe are major sources of dust in the Galactic interstellar medium and in external galaxies.},
doi = {10.1088/0004-637X/774/1/8},
journal = {Astrophysical Journal},
number = 1,
volume = 774,
place = {United States},
year = {Sun Sep 01 00:00:00 EDT 2013},
month = {Sun Sep 01 00:00:00 EDT 2013}
}
  • The mass of the Crab Nebula pulsar is determined to be 2 M/sub sun/ by solving a complete set of equations for nebular brightness and dynamics; the star's dipole moment of inertia obtains for the nearly incompressible star. The theoretical optical brightness agrees in detail with sufficient data to allow for a priori prediction of X-ray brightness. The theory is predicated in terms of a simple magnetic dipolar radiating neutron star and basic postulates.
  • We investigate through hydrodynamic simulations the destruction of newly formed dust grains by sputtering in the reverse shocks of supernova (SN) remnants. Using an idealized setup of a planar shock impacting a dense, spherical clump, we implant a population of Lagrangian particles into the clump to represent a distribution of dust grains in size and composition. We then post-process the simulation output to calculate the grain sputtering for a variety of species and size distributions. We explore the parameter space appropriate for this problem by altering the overdensity of the ejecta clumps and the speed of the reverse shocks. Sincemore » radiative cooling could lower the temperature of the medium in which the dust is embedded and potentially protect the dust by slowing or halting grain sputtering, we study the effects of different cooling methods over the timescale of the simulations. In general, our results indicate that grains with radii less than 0.1 {mu}m are sputtered to much smaller radii and often destroyed completely, while larger grains survive their interaction with the reverse shock. We also find that, for high ejecta densities, the percentage of dust that survives is strongly dependent on the relative velocity between the clump and the reverse shock, causing up to 50% more destruction for the highest velocity shocks. The fraction of dust destroyed varies widely across grain species, ranging from total destruction of Al{sub 2}O{sub 3} grains to minimal destruction of Fe grains (only 20% destruction in the most extreme cases). C and SiO{sub 2} grains show moderate to strong sputtering as well, with 38% and 80% mass loss. The survival rate of grains formed by early SNe is crucial in determining whether or not they can act as the 'dust factories' needed to explain high-redshift dust.« less
  • Shortly after its outburst, the authors suggested that supernova 1987a might condense a dust shell of substantial visual optical thickness as many classical novae do and predicted that dust might form within a year after the explosion. A critical examination of recent optical and infrared observations reported by others confirms that dust grains had begun to grow at a temperature of 1,000 K after 300 days and that the dust shell had become optically thick by day 600. After day 600, the infrared luminosity closely followed the intrinsic luminosity expected for thermalized {sup 56}Co {gamma} rays, demonstrating that the luminositymore » is powered by radioactivity and that the dust is outside the radioactivity zone. The infrared luminosity sets an upper limit to the soft intrinsic bolometric luminosity of a pulsar central engine. This upper limit for the pulsar in supernova 1987a is the same luminosity as the Crab pulsar has today 936 years after its formation. It is unlikely that the rotation rate for a pulsar in supernova 1987a can be much higher than {approx}30 revolutions per sec. The relatively long time required for the shell to grow to maximum optical depth as compared with the dust in nova shells may be related to the relatively low outflow velocity of the condensible ejecta.« less
  • We present Spitzer Infrared Spectrograph and Infrared Array Camera observations of the young supernova remnant E0102 (SNR 1E0102-7219) in the Small Magellanic Cloud. The infrared spectra show strong lines of Ne and O, with the [Ne II] line at 12.8 {mu}m having a large velocity dispersion of 2000-4500 km s{sup -1} indicative of fast-moving ejecta. Unlike the young Galactic SNR Cas A, E0102 lacks emission from Ar and Fe. Diagnostics of the observed [Ne III] line pairs imply that [Ne III] emitting ejecta have a low temperature of 650 K, while [Ne V] line pairs imply that the infrared [Nemore » V] emitting ejecta have a high density of {approx}10{sup 4} cm{sup -3}. We have calculated radiative shock models for various velocity ranges including the effects of photoionization. The shock model indicates that the [Ne V] lines come mainly from the cooling zone, which is hot and dense, whereas [Ne II] and [Ne III] come mainly from the photoionization zone, which has a low temperature of 400-1000 K. We estimate an infrared-emitting Ne ejecta mass of 0.04 M{sub sun} from the infrared observations, and discuss implications for the progenitor mass. The spectra also have a dust continuum feature peaking at 18 {mu}m that coincides spatially with the ejecta, providing evidence that dust formed in the expanding ejecta. The 18 {mu}m peak dust feature is fitted by a mixture of MgSiO{sub 3} and Si dust grains, while the rest of the continuum requires either carbon or Al{sub 2}O{sub 3} grains. We measure the total dust mass formed within the ejecta of E0102 to be {approx}0.014 M{sub sun}. The dust mass in E0102 is thus a factor of a few smaller than that in Cas A. The composition of the dust is also different, showing relatively less silicate and likely no Fe-bearing dust, as is suggested by the absence of Fe-emitting ejecta.« less