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(Abridged) The galaxy cluster Abell 2218, at z=0.171, is well-known for thediscrepancy between mass estimates derived from X-ray and strong lensinganalyses. With the present XMM observation, we trace the gas density andtemperature profiles out to a radius of ~ 1400 h_70^-1 kpc (approximately thevirial radius of the cluster). The surface brightness profile is well fittedover three orders of magnitude with a beta model, with a core radius of 0.'95and \beta=0.63. The projected temperature profile declines steeply with radius(by ~50%), and is well described by a polytrope with parameters t_0=8.09 keVand \gamma=1.15. The temperature map shows a pronounced peak in the centralarcminute, with an increase of a factor of two (from ~5 to ~10 keV). The massprofile, calculated assuming hydrostatic equilibrium and spherical symmetry, isbest fitted with a King approximation to an isothermal sphere, implying a darkmatter distribution with a central core, in contrast with the cusped coresfound in more obviously relaxed clusters. The X-ray mass is two times less thanthe strong lensing mass at r ~ 80 h_50^-1 kpc, although the agreement betweenX-ray and weak lensing mass measurements at larger radius (r ~ 400 h_50^-1 kpc)is slightly better. While the X-ray total mass estimates can vary by 30%depending on the mass model, all measurements are lower than the correspondingtotal mass from optical measurements. Given the X-ray results indicatingdisturbance of the intracluster gas, leading to a likely violation of theassumption of hydrostatic equilibrium, and the observed substructure in theoptical, suggesting a line-of-sight merger, it is unlikely that the differentmass estimates of this cluster can be reconciled, at least with standardmodelling assumptions.Comment: 9 pages, 7 figures; to appear in A&

Further evidence for a merger in Abell 2218 from anXMM-Newtonobservation