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Papilio glaucus
This is a lovely butterfly! However, I believe this is actually a dark morph female Eastern Tiger Swallowtail. The color pattern and shape is consistent: http://bugguide.net/node/view/1486
The chances of this being Papillio astyalus are very slim. The color pattern is a bit different than those of the images on BugGuide as well. The Broad-banded Swallowtail is found in subtropical climate and occasionally strays into the very southern states (Texas, Arizona). This would be way out of range for this species. Here is one of the images from BugGuide. Note the double orange crescents on the hindwings (yours only has single spots): http://bugguide.net/node/view/63177