  The rotation state of small asteroids is affected by the
Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, which is a net torque
caused by solar radiation directly reflected and thermally reemitted from the
surface. Due to this effect, the rotation period slowly changes, which can be
most easily measured in light curves because the shift in the rotation phase
accumulates over time quadratically. We collected archived light curves and
carried out new photometric observations for asteroids (10115) 1992 SK, (1620)
Geographos, and (1685) Toro. We applied the method of light curve inversion to
fit observations with a convex shape model. The YORP effect was modeled as a
linear change of the rotation frequency $\upsilon \equiv \mathrm{d}\omega /
\mathrm{d}t$ and optimized together with other spin and shape parameters. We
detected the acceleration $\upsilon = (8.3 \pm 0.6) \times
10^{-8}\,\mathrm{rad}\,\mathrm{d}^{-2}$ of the rotation for asteroid (10115)
1992 SK. This observed value agrees well with the theoretical value of
YORP-induced spin-up computed for our shape and spin model. For (1685) Toro, we
obtained $\upsilon = (3.3 \pm 0.3) \times
10^{-9}\,\mathrm{rad}\,\mathrm{d}^{-2}$, which confirms an earlier tentative
YORP detection. For (1620) Geographos, we confirmed the previously detected
YORP acceleration and derived an updated value of $\upsilon$ with a smaller
uncertainty. We also included the effect of solar precession into our inversion
algorithm, and we show that there are hints of this effect in Geographos' data.
The detected change of the spin rate of (10115) 1992 SK has increased the total
number of asteroids with YORP detection to ten. In all ten cases, the
$\mathrm{d}\omega / \mathrm{d}t$ value is positive, so the rotation of these
asteroids is accelerated. It is unlikely to be just a statistical fluke, but it
is probably a real feature that needs to be explained.
