Good answers from everyone here!
Yup, that's a Gulf Fritillary and if you want to see more of them, plant their host plant, Passion Vine (Passiflora spp.). I just wanted to mention that butterflies are adults when they emerge. The juvenile form is the caterpillar. When a butterfly emerges, it will never grow any larger, and won't change pattern except for loss of scales due to age, weather, tangling with predators, etc. I get that question a lot so I thought I'd throw that out there.
Remember, milkweed is also a great nectar plant so it's going to attract many butterflies other than Monarchs. And that's a good thing!