Low-Frequency Observations of Galactic Supernova Remnants and the Distribution of Low-Density Ionized Gas in the Interstellar Medium

Abstract

New long-wavelength observations of Galactic supernova remnants (SNRs) at 30.9 and 57.5 MHz are used to derive detailed low-frequency radio spectra for 32 SNRs. Of these, approximately two-thirds show turnovers at low frequencies, implying the presence of a widespread, but inhomogeneous, ionized absorbing medium along the lines of sight. These observations are combined with other low-frequency data to derive free-free optical depths toward 47 SNRs and to constrain the physical properties of the ionized gas responsible for the absorption. Three generally accepted ionized components of the interstellar medium (ISM) which absorb low-frequency radio emission are (1) H II regions; (2) extended H II region envelopes (EHEs); and (3) the warm ionized medium (WIM).

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Document Details

Document Type
Technical Report
Publication Date
Dec 15, 1989
Accession Number
ADA464488

Entities

People

  • Namir E. Kassim

Organizations

  • United States Naval Research Laboratory

Tags

DTIC Thesaurus Topics

  • Abstracts
  • Frequency
  • Gases
  • Information Operations
  • Ionized Gases
  • Long Wavelengths
  • Low Density
  • Military Research
  • Observation
  • Physical Properties

Fields of Study

  • Physics

Readers

  • Astronomy/Astrophysics

Technology Areas

  • Space