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Session 61 - Formation and Structure of the Milky Way.
Oral session, Tuesday, January 14
We have reprocessed archival 333 MHz VLA data with wide-field imaging software and uncovered the meter wavelength counterpart to the Northern Galactic Lobe first identified by LaRosa and Kassim at 80 MHz. With its morphology much better defined on the VLA 333 MHz image we have been able to follow the source in emission from 57.5 MHz to 15 GHz and construct a new spectrum with power law index -0.56. This is a significantly flatter spectrum than the \alpha \leq -1 originally estimated using only the very low frequency maps and poorly constrained upper limit flux densities from single-dish, centimeter wavelength maps. The revised spectrum and far better delineated shell-like morphology now favor re-interpretation of the Northern Galactic Lobe as the supernova remnant G0.33+0.04. Furthermore the low frequency turnover in the continuum spectrum implies that the source is located physically close to the Galactic Center. Though it is larger and thus presumably older than Sgr A East, the commonly derived physical properties of G0.33+0.04, including its continuum spectrum, surface brightness, morphology, and implied physical size, radio luminosity, and equipartition minimum energy are typical of other shell-type, Galactic SNRs. We do note that G0.33+0.04 is brightest where it nearly overlaps the northwest portion of the Galactic Center Arc, suggesting some type of physical interaction. Finally, while we find no compelling evidence to force us to interpret G0.33+0.04 as anything else besides a normal SNR, we note that alternative interpretations of Sgr A East do exist which may also apply to this source. In order to test these models estimates of the density of the gas into which G0.33+0.04 is expanding are needed so we can place better limits on its energetics and perhaps its age.
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Program listing for Tuesday