Global Far-Ultraviolet Properties of the Cygnus Loop

Abstract

We present the C III λ977, O VI λλ1032, 1038 and N IV] λ1486 emission line maps of the Cygnus Loop, obtained with the newly processed data of Spectroscopy of Plasma Evolution from Astrophysical Radiation (SPEAR; also known as FIMS) mission. In addition, the Si IV+O IV] line complexes around 1400 Å are resolved into two separate emission lines, whose intensity demonstrates a relatively high Si IV region predicted in the previous study. The morphological similarity between the O VI and X-ray images, as well as a comparison of the O VI intensity with the value expected from the X-ray results, indicates that large portions of the observed O VI emissions could be produced from X-ray emitting gas. Comparisons of the far-ultraviolet (FUV) images with the optical and H I 21 cm images, reveal spatial variations of shock-velocity populations and high FUV extinction in the direction of a previously identified H I cloud. By calculating the FUV line ratios for several subregions of the Cygnus Loop, we investigate the spatial variation of the population of radiative shock velocities; and the effects of resonance scattering, X-ray emitting gas, and non-radiative shocks. The FUV and X-ray luminosity comparisons between the Cygnus Loop and the Vela supernova remnant suggest that the fraction of shocks in the early evolutionary stages is much larger in the Cygnus Loop.

8 pages, 4 figures, 1 table. accepted for publication in ApJ

References in corpus (8)

• The MAPPINGS III Library of Fast Radiative Shock Models
• The SPEAR Instrument and On-Orbit Performance
• The Spectroscopy of Plasma Evolution from Astrophysical Radiation Mission
• Shock Speed, Cosmic Ray Pressure, and Gas Temperature in the Cygnus Loop
• The Plasma Structure of the Cygnus Loop from the Northeastern Rim to the Southwestern Rim
• Chandra Observations of the Northeastern Rim of the Cygnus Loop
• SPEAR Far Ultraviolet Spectral Images of the Cygnus Loop
• The Plasma Structure of the Southwestern Region of the Cygnus Loop with the XMM-Newton Observatory

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