  In photometry of $\gamma$ Cas (B0.5 IVe) from the SMEI and
BRITE-Constellation satellites, indications of low-order non-radial pulsation
have recently been found, which would establish an important commonality with
the class of classical Be stars at large. New photometry with the TESS
satellite has detected three frequency groups near 1.0 ($g1$), 2.4 ($g2$), and
5.1 ($g3$) d$^{-1}$, respectively. Some individual frequencies are nearly
harmonics or combination frequencies but not exactly so. Frequency groups are
known from roughly three quarters of all classical Be stars and also from
pulsations of $\beta$ Cep, SPB, and $\gamma$ Dor stars and, therefore, firmly
establish $\gamma$ Cas as a non-radial pulsator. The total power in each
frequency group is variable. An isolated feature exists at 7.57 d$^{-1}$ and,
together with the strongest peaks in the second and third groups ordered by
increasing frequency ($g2$ and $g3$), is the only one detected in all three
TESS sectors. The former long-term 0.82 d$^{-1}$ variability would fall into
$g1$ and has not returned at a significant level, questioning its attribution
to rotational modulation. Low-frequency stochastic variability is a dominant
feature of the TESS light curve, possibly caused by internal gravity waves
excited at the core-envelope interface. These are known to be efficient at
transporting angular momentum outward, and may also drive the oscillations that
constitute $g1$ and $g2$. The hard X-ray flux of $\gamma$ Cas is the only
remaining major property that distinguishes this star from the class of
classical Be stars.
