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D.A. Leahy (University of Calgary), R.S. Roger (DRAO/HIA/National Research Council Canada)
An emission component associated with supernova remnants which, to date, has not received much attention, is the 21 cm neutral hydrogen (HI) line. This is, in part, due to the complexity of the HI and interpreting its association with a supernova remnant. The main previous study of the Cygnus Loop in HI is that of DeNoyer (1975, ApJ 196, 479). Here we present an analysis of 21 cm neutral hydrogen line observations of the Cygnus Loop taken with the Dominion Radio Astrophysical Observatory's Synthesis Telescope and 26 m Telescope. Spectral line maps in 128 channels with 1.65 km/s velocity separation were constructed for a 6 degree square field encompassing the Cygnus Loop. The region in and around the Cygnus Loop is rich in HI features, including clouds and shells. We list the most prominent features and discuss their origin. Several strong features are found which have interior edges closely matching the outer boundary of the Cygnus Loop. These are likely the definitive evidence for much of the wall of the cavity into which the Cygnus Loop is hypothesized to be expanding. We also find HI associated with the radio continuum ``serpent'' feature, located near the center of the Cygnus Loop. The overall properties of the HI emission, such as HI mass and velocity distribution, are also summarized. We find evidence for an HI cavity associated with the interior of the Cygnus Loop.
This work supported in part by the Natural Sciences and Engineering Research Council of Canada.
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