The minimum required CPU is a 2.4GHz dual core, though I have seen reports of the game running on CPUs as low as 2.0GHz. One person reported crashes on startup with a 1.7GHz CPU, but in that case the GPU was also below spec (and a PC). Stauff1138 may have an idea if or how well it may run.
The next update should include some multithreading optimizations to take better advantage of multi-core CPUs, but I don't know if that would be enough to help with a 1.3GHz CPU.
