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We measured the optical phase curve of the transiting brown dwarf KELT-1b(TOI 1476, Siverd et al. 2012) using data from the TESS spacecraft. We foundthat KELT-1b shows significant phase variation in the TESS bandpass, with arelatively large phase amplitude of $234^{+43}_{-44}$ ppm and a secondaryeclipse depth of $371^{+47}_{-49}$ ppm. We also measured a marginal eastwardoffset in the dayside hotspot of $18.3^\circ\pm7.4^\circ$ relative to thesubstellar point. We detected a strong phase curve signal attributed toellipsoidal distortion of the host star, with an amplitude of $399\pm19$ ppm.Our results are roughly consistent with the Spitzer phase curves of KELT-1b(Beatty et al. 2019), but the TESS eclipse depth is deeper than expected. Ourcloud-free 1D models of KELT-1b's dayside emission are unable to fit the fullcombined eclipse spectrum. Instead, the large TESS eclipse depth suggests thatKELT-1b may have a significant dayside geometric albedo of$\mathrm{A}_\mathrm{g}\sim0.5$ in the TESS bandpass, which would agree with thetentative trend between equilibrium temperature and geometric albedo recentlysuggested by Wong et al. 2020. We posit that if KELT-1b has a high daysidealbedo, it is likely due to silicate clouds (Gao et al. 2020) that form onKELT-1b's nightside (Beatty et al. 2019, Keating et al. 2019) and aresubsequently transported onto the western side of KELT-1b's dayside hemispherebefore breaking up.

The TESS Phase Curve of KELT-1b Suggests a High Dayside Albedo