  We present the first attempt to fit the light curve of the interstellar
visitor `Oumuamua using a physical model which includes optional torque. We
consider both conventional (Lommel-Seeliger triaxial ellipsoid) and alternative
("black-and-white ball", "solar sail") brightness models. With all the
brightness models, some torque is required to explain the timings of the most
conspicuous features -- deep minima -- of the asteroid's light curve. Our
best-fitting models are a thin disc (aspect ratio 1:6) and a thin cigar (aspect
ratio 1:8) which are very close to being axially symmetric. Both models are
tumbling and require some torque which has the same amplitude in relation to
`Oumuamua's linear non-gravitational acceleration as in Solar System comets
which dynamics is affected by outgassing. Assuming random orientation of the
angular momentum vector, we compute probabilities for our best-fitting models.
We show that cigar-shaped models suffer from a fine-tuning problem and have
only 16 per cent probability to produce light curve minima as deep as the ones
present in `Oumuamua's light curve. Disc-shaped models, on the other hand, are
very likely (at 91 per cent) to produce minima of the required depth. From our
analysis, the most likely model for `Oumuamua is a thin disc (slab)
experiencing moderate torque from outgassing.
