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C. L. Brogan, K. K. Dyer (NRAO), N. E. Kassim, T. J. Lazio (NRL), C. K. Lacey (USC)
We present VLA images of the supernova remnant (SNR) 3C391 at 74, 330, and 1400 MHz. This remnant has been known for some time to exhibit a turnover in its radio continuum spectrum at frequencies < 100 MHz, indicative of free-free absorption from ionized gas along the line of sight. The subsequent detection of weak radio recombination lines toward this source supported this hypothesis. For the first time, our data show the spatially resolved morphology of the low frequency absorption at 74 MHz with a resolution of ~70\arcsec. Against expectation that such absorption arises from unrelated low density \ion{H}{2} regions along the line of sight, these data suggest that the absorbing medium is directly linked to the SNR itself. This remnant has been shown in a number of recent papers to be interacting with a molecular cloud. Indeed, it exhibits a number of signposts of SNR/molecular cloud shocks including OH (1720 MHz) masers and broad molecular emission lines. Comparison of the regions of strongest 74 MHz absorption with existing X-ray, IR, and molecular data suggests that the free-free absorption originates from the SNR/molecular cloud shock boundaries. This makes 3C391 just the third SNR for which such spatially resolved absorption has been measured, and the only one for which the absorption is thought to arise from a SNR/molecular cloud interface region. We also present spectral index maps of 3C391 between 330 and 1400 MHz of 3C391 with unprecedented sensitivity.
The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities Inc. Basic research in radio astronomy at the Naval Research Laboratory is supported by the Office of Naval Research.
The author(s) of this abstract have provided an email address for comments about the abstract: cbrogan@aoc.nrao.edu
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.