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I.M. Hoffman (UNM), M.J. Claussen (NRAO), W.M. Goss (NRAO), A.M.S. Richards (NRAL)
Two observations of the 1720\ {\rm MHz} maser emission from the OH molecule in the supernova remnant IC~443 (G189.1+3.0) are discussed. We present separate results from the VLBA + phased VLA and from six antennas of the MERLIN radio telescope array. The MERLIN array was able to resolve some of the maser emission regions showing imaged sizes of 115\ {\rm mas} < \theta < 230\ {\rm mas}. The visibility data from the VLBA + phased VLA indicate sources sizes {~180\ {\rm mas}. Since interstellar image scatter-broadening is expected to be minimal towards IC~443, near the Galactic anticenter, these measured sizes are likely the intrinsic sizes of the maser regions. Based on the assumption that the IC~443 OH sources are not scatter-broadened at the relatively small distance of 1.5\ {\rm kpc}, these data are the the most reliable determination of the intrinsic size of OH (1720\ {\rm MHz}) masers in supernova remnants. These measurements indicate that 1720\ {\rm MHz} OH maser regions in supernova remnants have, in general, linear sizes approaching {~300\ {\rm AU}.
This research was supported by the National Radio Astronomy Observatory (NRAO) summer student program. The NRAO is a facility of the National Science Foundation and is operated by Associated Universities, Inc.\ under contract.
The author(s) of this abstract have provided an email address for comments about the abstract: ian@as.unm.edu