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Title:
Spitzer Spectroscopy of the Galactic Supernova Remnant G292.0+1.8: Structure and Composition of the Oxygen-Rich Ejecta
Authors:
Ghavamian, Parviz; Raymond, John C.; Blair, William P.; Long, Knox S.; Tappe, Achim; Park, Sangwook; Winkler, P. Frank
Affiliation:
AA(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA ), AB(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA ), AC(Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA ), AD(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA ), AE(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA ), AF(Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802, USA ), AG(Department of Physics, Middlebury College, McCardell Bicentennial Hall 526, Middlebury, VT 05753, USA )
Publication:
The Astrophysical Journal, Volume 696, Issue 2, pp. 1307-1318 (2009). (ApJ Homepage)
Publication Date:
05/2009
Origin:
IOP
ApJ Keywords:
cosmic rays, ISM: individual: G292.0+1.8, ISM: kinematics and dynamics, plasmas, shock waves, supernova remnants
DOI:
10.1088/0004-637X/696/2/1307
Bibliographic Code:
2009ApJ...696.1307G

Abstract

We present mid-infrared (mid-IR; 5-40 μm) spectra of shocked ejecta in the Galactic oxygen-rich supernova remnant (SNR) G292.0+1.8, acquired with the Infrared Spectrograph onboard the Spitzer Space Telescope. The observations targeted two positions within the brightest oxygen-rich feature in G292.0+1.8. Emission lines of [Ne II] λ12.8, [Ne III] λλ15.5,36.0, [Ne V] λ24.3, and [O IV] λ25.9 μm are detected from the shocked ejecta. In marked contrast to what is observed in Cassiopeia A, no discernible mid-IR emission from heavier species such as Mg, Si, S, Ar, or Fe is detected in G292.0+1.8. We also detect a broad emission bump between 15 and 28 μm in spectra of the radiatively shocked O-rich ejecta in G292.0+1.8. We suggest that this feature arises from either shock-heated Mg2SiO4 (forsterite) dust in the radiatively shocked O-rich ejecta or collisional excitation of polycyclic aromatic hydrocarbons in the blast wave of the SNR. If the former interpretation is correct, this would be the first mid-IR detection of ejecta dust in G292.0+1.8. A featureless dust continuum is also detected from nonradiative shocks in the circumstellar medium around G292.0+1.8. The mid-IR continuum from these structures, which lack mid-IR line emission, is seen in Chandra images as bright X-ray filaments, is well described by a two-component silicate dust model. The temperature of the hot dust component (M d ~ 2 × 10-3 M sun) is ~115 K, while that of the cold component (roughly constrained to be lsim3 M sun) is ~35 K. We attribute the hot component to collisionally heated dust in the circumstellar shocks in G292.0+1.8, and attribute the cold component to dust heated by the hard FUV radiation from the circumstellar shocks. Using average O/Ne and O/Si mass ratios measured for a sample of ejecta knots in the X-rays, our models yield line strengths consistent with mass ratios M O/M Ne ≈ 3, M O/M Si gsim 61, and M O/M S ≈ 50. These ratios (especially the large O/Ne mass ratio) are difficult to reproduce with standard nucleosynthesis models of well-mixed supernova ejecta. This reinforces the conclusions of existing X-ray studies that the reverse shock in G292.0+1.8 is currently propagating into the hydrostatic nucleosynthetic layers of the progenitor star, and has not yet penetrated the layers dominated by explosive nucleosynthetic products.
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