  We report on an XMM-Newton observation of RX J1347.5-1145 (z=0.451), the most
luminous X-ray cluster of galaxies currently known, with a luminosity L_X = 6.0
\pm 0.1 \times 10^45 erg/s in the [2-10] keV energy band. We present the first
temperature map of this cluster, which shows a complex structure. It identifies
the cool core and a hot region at radii 50-200 kpc to south-east of the main
X-ray peak, at a position consistent with the subclump seen in the X-ray image.
This structure is probably an indication of a submerger event. Excluding the
data of the south-east quadrant, the cluster appears relatively relaxed and we
estimate a total mass within 1.7 Mpc of 2.0 \pm 0.4 \times 10^15 M_sun. We find
that the overall temperature of the cluster is kT=10.0 \pm 0.3 keV. The
temperature profile shows a decline in the outer regios and a drop in the
centre, indicating the presence of a cooling core which can be modelled by a
cooling flow model with a minimum temperature ~2 keV and a very high mass
accretion rate, \dot{M} ~ 1900 M_sun/yr. We compare our results with previous
observations from ROSAT, ASCA and Chandra.
