  The rotation states of small asteroids are affected by a net torque arising
from an anisotropic sunlight reflection and thermal radiation from the
asteroids' surfaces. On long timescales, this so-called YORP effect can change
asteroid spin directions and their rotation periods. We analyzed lightcurves of
four selected near-Earth asteroids with the aim of detecting secular changes in
their rotation rates that are caused by YORP. We use the lightcurve inversion
method to model the observed lightcurves and include the change in the rotation
rate $\mathrm{d} \omega / \mathrm{d} t$ as a free parameter of optimization. We
collected more than 70 new lightcurves. For asteroids Toro and Cacus, we used
thermal infrared data from the WISE spacecraft and estimated their size and
thermal inertia. We also used the currently available optical and radar
astrometry of Toro, Ra-Shalom, and Cacus to infer the Yarkovsky effect. We
detected a YORP acceleration of $\mathrm{d}\omega / \mathrm{d} t = (1.9 \pm
0.3) \times 10^{-8}\,\mathrm{rad}\,\mathrm{d}^{-2}$ for asteroid Cacus. For
Toro, we have a tentative ($2\sigma$) detection of YORP from a significant
improvement of the lightcurve fit for a nonzero value of $\mathrm{d}\omega /
\mathrm{d} t = 3.0 \times 10^{-9}\,\mathrm{rad}\,\mathrm{d}^{-2}$. For asteroid
Eger, we confirmed the previously published YORP detection with more data and
updated the YORP value to $(1.1 \pm 0.5) \times
10^{-8}\,\mathrm{rad}\,\mathrm{d}^{-2}$. We also updated the shape model of
asteroid Ra-Shalom and put an upper limit for the change of the rotation rate
to $|\mathrm{d}\omega / \mathrm{d} t| \lesssim 1.5 \times
10^{-8}\,\mathrm{rad}\,\mathrm{d}^{-2}$. Ra-Shalom has a greater than $3\sigma$
Yarkovsky detection with a theoretical value consistent with observations
assuming its size and/or density is slightly larger than the nominally expected
values.
