Is it possible to have lightning without thunder?

No. Thunder is produced when a flash of lightning passes through the air, heating the adjacent air and causing it to expand rapidly. A short flash creates a short burst of thunder. Rolling thunder occurs when a long flash generates thunder over a great distance or when obstructions cause echoes and reverberations. Often on a clear night, there is heat lightning, when accompanying thunder is too distant to be audible, but it nevertheless does occur.