Papaya is semitropical and tropical fruit which can with stand some cold temperature. It is problem only when temperature drops below 0 °C (below 32 °F) because papaya won't tolerate freezing temperature. I assume it is not the problem in your region since the winter temperature is between 9–11 °C (48–52 °F).
If the temperature drops further you can cover the tree with plastic sheets. Also provide proper nutrients and water so that tree can withstand any stress due to fluctuation in temperature. Mulching will also help.