All external flase can act as slave, you just need to buy the slave unit and attach the flash to it. But the tricky thing is to set your camera to do a slow shutter speed shot, this is so the when the slave fires the shutter will still be open to capture the flash. Using a slave is fun, you can experiment on different location for the slave unit. Have fun.
In the current subject "panning" will also blur the subject. This is because the subject is NOT travelling in a straight line , but in a curve, so it is quite difficult to get the subject sharp. Maybe if you are lucky, using a shorter exposure to reduce the subject's movement.
Panning is a technique of using a long exposure (slow shutter speed) while moving the camera.