In general, I've been taught that if you're faced with a big cat the best thing to do is to try to scare it (so long as it's not cornered). Make yourself as large and loud as possible and whatever you do, do not run from it. Grab a stick and flail your arms, throw rocks at it, etc.. That being said, it can be hard with a horse involved.
Also, it sounds like this cat may not be your typical wild cat and may be either driven by hunger, not right in the head or just grown too comfortable around humans. A gun would be the best option, even if you only had blanks. It would have to be a bat poop crazy cat to not run from the noise.