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In this paper, we investigate the nonprincipal axis (NPA) rotational state of1I/`Oumuamua -- the first interstellar object discovered traversing the innerSolar System -- from its photometric light curve. Building upon Mashchenko(2019), we develop a model which incorporates NPA rotation and {Sun-induced,time-varying} outgassing torques to generate synthetic light curves of theobject. The model neglects tidal forces, which are negligible compared tooutgassing torques over the distances that `Oumuamua was observed. We implementan optimization scheme that incorporates the NPA rotation model to calculatethe initial rotation state of the object. We find that an NPA rotation statewith an average period of $\langle P \rangle\simeq7.34$ hr best reproduces thephotometric data. The discrepancy between this period and previous estimates isdue to continuous period modulation induced by outgassing torques in therotational model, {as well as different periods being used}. The best fit tothe October 2017 data does not reproduce the November 2017 data (although thelater measurements are too sparse to fit). The light curve is consistent withno secular evolution of the angular momentum, somewhat in tension with theempirical correlations between nuclear spin-up and cometary outgassing. Thecomplex rotation of `Oumuamua may be {the result of primordial rotation aboutthe smallest principal axis} if (i) the object experienced hypervolatileoutgassing and (ii) our idealized outgassing model is accurate.

Fitting the Light Curve of 1I/`Oumuamua with a Nonprincipal Axis Rotational Model and Outgassing Torques