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Title: Spitzer IRS observations of the XA region in the cygnus loop supernova remnant

Abstract

We report on spectra of two positions in the XA region of the Cygnus Loop supernova remnant obtained with the InfraRed Spectrograph on the Spitzer Space Telescope. The spectra span the 10-35 μm wavelength range, which contains a number of collisionally excited forbidden lines. These data are supplemented by optical spectra obtained at the Whipple Observatory and an archival UV spectrum from the International Ultraviolet Explorer. Coverage from the UV through the IR provides tests of shock wave models and tight constraints on model parameters. Only lines from high ionization species are detected in the spectrum of a filament on the edge of the remnant. The filament traces a 180 km s{sup –1} shock that has just begun to cool, and the oxygen to neon abundance ratio lies in the normal range found for Galactic H II regions. Lines from both high and low ionization species are detected in the spectrum of the cusp of a shock-cloud interaction, which lies within the remnant boundary. The spectrum of the cusp region is matched by a shock of about 150 km s{sup –1} that has cooled and begun to recombine. The post-shock region has a swept-up column density of about 1.3 ×more » 10{sup 18} cm{sup –2}, and the gas has reached a temperature of 7000-8000 K. The spectrum of the Cusp indicates that roughly half of the refractory silicon and iron atoms have been liberated from the grains. Dust emission is not detected at either position.« less

Authors:
 [1]; ;  [2];  [3];  [4];  [5];  [6];  [7]
  1. SOFIA Science Center, NASA Ames Research Center, M/S N211-3, Moffett Field, CA 94035 (United States)
  2. Smithsonian Astrophysical Observatory, 60 Garden Street, MS 15, Cambridge, MA 02138 (United States)
  3. Department of Physics, Western Michigan University, Kalamazoo MI 49008-5252 (United States)
  4. Goddard Space Flight Center, Mail Code 662, Greenbelt, MD 20771 (United States)
  5. Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States)
  6. North Carolina State University, Raleigh, NC 27607 (United States)
  7. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
Publication Date:
OSTI Identifier:
22356890
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 787; 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; ABUNDANCE; CUSPED GEOMETRIES; DENSITY; DUSTS; EMISSION; FILAMENTS; IRON; LIMITING VALUES; NEON; OXYGEN; REFRACTORIES; SHOCK WAVES; SILICON; SPACE; SUPERNOVA REMNANTS; ULTRAVIOLET RADIATION; ULTRAVIOLET SPECTRA; WAVELENGTHS

Citation Formats

Sankrit, Ravi, Raymond, John C., Gaetz, Terrance J., Bautista, Manuel, Williams, Brian J., Blair, William P., Borkowski, Kazimierz J., and Long, Knox S.. Spitzer IRS observations of the XA region in the cygnus loop supernova remnant. United States: N. p., 2014. Web. doi:10.1088/0004-637X/787/1/3.
Sankrit, Ravi, Raymond, John C., Gaetz, Terrance J., Bautista, Manuel, Williams, Brian J., Blair, William P., Borkowski, Kazimierz J., & Long, Knox S.. Spitzer IRS observations of the XA region in the cygnus loop supernova remnant. United States. doi:10.1088/0004-637X/787/1/3.
Sankrit, Ravi, Raymond, John C., Gaetz, Terrance J., Bautista, Manuel, Williams, Brian J., Blair, William P., Borkowski, Kazimierz J., and Long, Knox S.. Tue . "Spitzer IRS observations of the XA region in the cygnus loop supernova remnant". United States. doi:10.1088/0004-637X/787/1/3.
@article{osti_22356890,
title = {Spitzer IRS observations of the XA region in the cygnus loop supernova remnant},
author = {Sankrit, Ravi and Raymond, John C. and Gaetz, Terrance J. and Bautista, Manuel and Williams, Brian J. and Blair, William P. and Borkowski, Kazimierz J. and Long, Knox S.},
abstractNote = {We report on spectra of two positions in the XA region of the Cygnus Loop supernova remnant obtained with the InfraRed Spectrograph on the Spitzer Space Telescope. The spectra span the 10-35 μm wavelength range, which contains a number of collisionally excited forbidden lines. These data are supplemented by optical spectra obtained at the Whipple Observatory and an archival UV spectrum from the International Ultraviolet Explorer. Coverage from the UV through the IR provides tests of shock wave models and tight constraints on model parameters. Only lines from high ionization species are detected in the spectrum of a filament on the edge of the remnant. The filament traces a 180 km s{sup –1} shock that has just begun to cool, and the oxygen to neon abundance ratio lies in the normal range found for Galactic H II regions. Lines from both high and low ionization species are detected in the spectrum of the cusp of a shock-cloud interaction, which lies within the remnant boundary. The spectrum of the cusp region is matched by a shock of about 150 km s{sup –1} that has cooled and begun to recombine. The post-shock region has a swept-up column density of about 1.3 × 10{sup 18} cm{sup –2}, and the gas has reached a temperature of 7000-8000 K. The spectrum of the Cusp indicates that roughly half of the refractory silicon and iron atoms have been liberated from the grains. Dust emission is not detected at either position.},
doi = {10.1088/0004-637X/787/1/3},
journal = {Astrophysical Journal},
number = 1,
volume = 787,
place = {United States},
year = {Tue May 20 00:00:00 EDT 2014},
month = {Tue May 20 00:00:00 EDT 2014}
}
  • The XA region of the Cygnus Loop is a bright knot of X-ray emission on the eastern edge of the supernova remnant. The emission results from the interaction of the supernova blast wave with density enhancements at the edge of a precursor formed cavity. However, this interaction is complex given the irregular morphology of the cavity wall. To study the nature and origin of the X-ray emission, we use high spatial resolution images from Chandra. We extract spectra from these images to analyze the physical conditions of the plasma. Our goal is to probe the density of various regions tomore » form a picture of the cavity wall and characterize the interaction between this supernova and the local interstellar medium. We find that a series of regions along the edge of the X-ray emission appears to trace out the location of the cavity wall. The best-fit plasma models result in two temperature component equilibrium models for each region. The low-temperature components have densities that are an order of magnitude higher than the high-temperature components. The high-density plasma may exist in the cavity wall where it equilibrates rapidly and cools efficiently. The low-density plasma is interior to the enhancement and heated further by a reverse shock from the wall. Calculations of shock velocities and timescales since shock heating are consistent with this interpretation. Furthermore, we find a bright knot of emission indicative of a discrete interaction of the blast wave with a high-density cloud in the cavity wall with a size scale {approx}0.1 pc. Aside from this, other extractions made interior to the X-ray edge are confused by line-of-sight projection of various components. Some of these regions show evidence of detecting the cavity wall but their location makes the interpretation difficult. In general, the softer plasmas are well fit at temperatures (kT){approx} 0.11 keV, with harder plasmas at temperatures of (kT){approx} 0.27 keV. All regions displayed consistent metal depletions most notably in N, O, and Ne at an average of 0.54, 0.55, and 0.36 times solar, respectively.« less
  • We present an analysis of the gamma-ray measurements by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the region of the supernova remnant (SNR) Cygnus Loop (G74.0-8.5). We detect significant gamma-ray emission associated with the SNR in the energy band 0.2-100 GeV. The gamma-ray spectrum shows a break in the range 2-3 GeV. The gamma-ray luminosity is {approx} 1 x 10{sup 33} erg s{sup -1} between 1-100 GeV, much lower than those of other GeV-emitting SNRs. The morphology is best represented by a ring shape, with inner/outer radii 0{sup o}.7 {+-} 0{sup o}.1 and 1{sup o}.6more » {+-} 0{sup o}.1. Given the association among X-ray rims, H{alpha} filaments and gamma-ray emission, we argue that gamma rays originate in interactions between particles accelerated in the SNR and interstellar gas or radiation fields adjacent to the shock regions. The decay of neutral pions produced in nucleon-nucleon interactions between accelerated hadrons and interstellar gas provides a reasonable explanation for the gamma-ray spectrum.« less
  • Emission from vibrationally excited H2 has been discovered which is associated with the bright optical shock-excited filaments to the northeast of the Cygnus Loop supernova remnant. Infrared spectroscopy and infrared and optical narrow-band images of the shock-excited gas have been obtained in an effort to understand the mechanism of H2 excitation. A shock model with a magnetic precursor is proposed which explains quantitatively the observed H2 surface brightness, level population, and relation to optical emission. A shock with a magnetic precursor can also account for some of the anomalous properties of nonradiative shocks. 64 refs.
  • We present 24 {mu}m and 70 {mu}m images of a non-radiative shock in the Cygnus Loop supernova remnant, obtained with the Multiband Imaging Photometer on board the Spitzer Space Telescope. The observed emission is from dust grains heated in the post-shock region. The 70 {mu}m to 24 {mu}m flux ratio depends on the dust heating and the dust destruction rates, and thereby it is a sensitive tracer of the gas density and temperature in the shocked plasma. We model the dust emission and grain destruction in the post-shock flow, and find that the observed 70 {mu}m to 24 {mu}m fluxmore » ratios are produced for post-shock densities, n{sub H}{approx}2.0 cm{sup -3} and electron temperatures of about 0.20 keV. We find that about 35% of the dust has been destroyed in the shock, and that non-thermal sputtering (i.e. sputtering due to bulk motion of the grains relative to the gas) contributes significantly to the dust destruction.« less
  • We present 24 {mu}m and 70 {mu}m images of a non-radiative shock in the Cygnus Loop supernova remnant, obtained with the Multiband Imaging Photometer for Spitzer on board the Spitzer Space Telescope. The post-shock region is resolved in these images. The ratio of the 70 {mu}m to the 24 {mu}m flux rises from about 14 at a distance 0.'1 behind the shock front to about 22 in a zone 0.'75 further downstream, as grains are destroyed in the hot plasma. Models of dust emission and destruction using post-shock electron temperatures between 0.15 keV and 0.30 keV and post-shock densities, n{submore » H}{approx} 2.0 cm{sup -3}, predict flux ratios that match the observations. Non-thermal sputtering (i.e., sputtering due to bulk motion of the grains relative to the gas) contributes significantly to the dust destruction under these shock conditions. From the model calculations, we infer that about 35% by mass of the grains are destroyed over a 0.14 pc region behind the shock front.« less