low-gravity brown dwarfs which are thought to have longer rotation periods [e.g. @Vos2018]. In @Vos2019 we detected significant $J$-band variability in during two $\sim4$ hr epochs separated by 2 years. We measured an amplitude of $\sim1\%$ during both observations, and found no evidence for light curve evolution between the two epochs. Our *Spitzer* light curve appears sinusoidal over the entire observation, so it seems that both the $J$-band and mid-IR light curves are stable. Periodogram analysis of the ground-based $J$-band light curve suggested a rotation period of $3-6$ hr [@Vos2019], while in this paper we measure a period of $2.4\pm0.1$ hr. Both of the ground-based, $J$-band light curves have significant gaps in the data due to poor weather during the observation, and this may explain the discrepancy between the estimated ground-based $J$-band and measured *Spitzer* rotation period.

![image](amplitudes_ch1-eps-converted-to.pdf) ![image](amplitudes_ch2-eps-converted-to.pdf)

We detected $J$-band variability in in two epochs in @Vos2019. During each $\sim4$ hr observation, we detected a slow downward trend, with a maximum $J$-band amplitude of $\sim2\%$. Since we did not cover a full rotation period in either observation, our periodogram analysis constrained the period to $>5$ hr, which is consistent with our much longer *Spitzer* measurement of $15.07\pm0.2$ hr. 