  ASCA data are used to obtain two-dimensional gas temperature maps of A2256,
A2319, A2163 and A665. In all four, the temperature decreases significantly at
off-center distances of ~1 h^{-1} Mpc. Central regions of the two nearer
clusters A2256 and A2319 appear largely isothermal except for the cooler spots
coincident with the subunits in their X-ray surface brightness. Although the
existence of this substructure may suggest ongoing merger activity, no
asymmetric features in the temperature distribution resembling those in the
hydrodynamic merger simulations are apparent. In the outer parts of the
clusters, the temperature declines symmetrically with radius. In A2256 and
A2319, it follows a polytropic slope with gamma~1.3-1.5. This is somewhat
steeper than the simulations predict for a flat CDM universe and is closer to
the open universe predictions (Evrard etal 1996). The temperature drop is more
prominent in the outer regions of A2163 and A665 and appears even steeper than
adiabatic (although not inconsistent with it). If the gas in the outskirts of
these two clusters is indeed as cool as we measure, the cluster atmospheres
should be convectively unstable and transient. Also, such a steep temperature
profile could not possibly emerge if the gas was heated only via the release of
its own gravitational energy during infall. This may indicate the presence of
an additional heat source in the inner cluster, such as merger shocks
transferring energy from the dark matter to the gas.
