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Title: Electron-ion equilibrium and shock precursors in the northeast limb of the Cygnus Loop

We present an observational study using high-resolution echelle spectroscopy of collisionless shocks in the Cygnus Loop supernova remnant. Measured Hα line profiles constrain pre-shock heating processes, shock speeds, and electron-ion equilibration (T{sub e} /T{sub i} ). The shocks produce faint Hα emission line profiles, which are characterized by narrow and broad components. The narrow component is representative of the pre-shock conditions, while the broad component is produced after charge transfer between neutrals entering the shock and protons in the post-shock gas, thus reflecting the properties of the post-shock gas. We observe a diffuse Hα region extending about 2.'5 ahead of the shock with line width ∼29 km s{sup –1}, while the Hα profile of the shock itself consists of broader than expected narrow (36 km s{sup –1}) and broad (250 km s{sup –1}) components. The observed diffuse emission arises in a photoionization precursor heated to about 18,000 K by He I and He II emission from the shock, with additional narrow component broadening originating from a thin cosmic-ray precursor. Broad to narrow component intensity ratios of ∼1.0 imply full electron-ion temperature equilibration T{sub e} ≅ T{sub i} in the post-shock region. Broad component line widths indicate shock velocities of aboutmore » 400 km s{sup –1}. Combining the shock velocities with proper motions suggests that the distance to the Cygnus Loop is ∼890 pc, significantly greater than the generally accepted upper limit of 637 pc.« less
Authors:
; ; ; ;  [1] ;  [2]
  1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  2. Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Lab, Hanover, NH 03755 (United States)
Publication Date:
OSTI Identifier:
22365398
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 791; 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; ACCELERATION; COSMIC RADIATION; EMISSION; EQUILIBRIUM; ION TEMPERATURE; PHOTOIONIZATION; PROPER MOTION; PROTONS; RESOLUTION; SHOCK HEATING; SHOCK WAVES; SPECTROSCOPY; SUPERNOVA REMNANTS; VELOCITY