  A new determination of the temperature of the intergalactic medium over $3.9
\leq z \leq 4.3$ is presented. We applied the curvature method on a sample of
10 high resolution quasar spectra from the Ultraviolet and Visual Echelle
Spectrograph on the VLT/ESO. We measured the temperature at mean density by
determining the temperature at the characteristic overdensity, which is tight
function of the absolute curvature irrespective of $\gamma$. Under the
assumption of fiducial value of $\gamma = 1.4$, we determined the values of
temperatures at mean density $T_{0} = 7893^{+1417}_{-1226}$ K and $T_{0} =
8153^{+1224}_{-993}$ K for redshift range of $3.9 \leq z \leq 4.1$ and $4.1
\leq z \leq 4.3$, respectively. Even though the results show no strong
temperature evolution over the studied redshift range, our measurements are
consistent with an intergalactic medium thermal history that includes a
contribution from He II reionization.
