  Using hydrodynamical simulations coupled to a radiative transfer code, we
study the additional heating effects in the intergalactic medium (IGM) produced
by $z\sim 6$ quasars in their near-zones. If helium is predominantly in HeII to
begin with, both normalization ($T_0$) and slope ($\gamma$) of the IGM
effective equation-of-state get modified by the excess ionization from the
quasars. Using the available constraints on $T_0$ at $z\sim6$, we discuss
implications for the nature and epoch of HI and HeII reionization. We study the
extent of the HeIII region as a function of quasar age and show, for a typical
inferred age of $z \sim 6$ quasars (i.e. $\sim 10^8$ yrs), it extends up to 80%
of the HI proximity region. For these long lifetimes, the heating effects can
be detected even when all the HI lines from the proximity region are used.
Using the flux and curvature probability distribution functions (PDFs), we
study the statistical detectability of heating effects as a function of initial
physical conditions in the IGM. For the present sample size, cosmic variance
dominates the flux PDF. The curvature statistics is more suited to capturing
the heating effects beyond the cosmic variance, even if the sample size is half
of what is presently available.
