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We present an \xmm mosaic observation of the hot ($kT\sim6.5$ keV) and nearby($z=0.0881$) relaxed cluster of galaxies A478. We derive precise gas density,gas temperature, gas mass and total mass profiles up to $12\arcmin$ (about halfof the virial radius $R_{200}$). The gas density profile is highly peakedtowards the center and the surface brightness profile is well fitted by a sumof three $\beta$--models. The derived gas density profile is in excellentagreement, both in shape and in normalization, with the published Chandradensity profile (measured within $5\arcmin$ of the center). Projection and PSFeffects on the temperature profile determination are thoroughly investigated.The derived radial temperature structure is as expected for a cluster hosting acooling core, with a strong negative gradient at the cluster center. Thetemperature rises from $\sim2$ keV up to a plateau of $\sim6.5$ keV beyond 2'(i.e. $r>208\rm{kpc}=0.1 R_{200}$, $R_{200}=2.08$ Mpc being the virial radius).  From the temperature profile and the density profile and under the hypothesisof hydrostatic equilibrium, we derived the total mass profile of A478 down to0.01 and up to 0.5 the virial radius. We tested different dark matter modelsagainst the observed mass profile. The Navarro, Frenk & White(\cite{navarro97}) model is significantly preferred to other models. It leadsto a total mass of $M_{200}=1.1\times 10^{15}$ M$_\odot$ for a concentrationparameter of $c=4.2\pm0.4$. The gas mass fraction slightly increases withradius. The gas mass fraction at a density contrast of $\delta=2500$ is$\fgas=0.13\pm0.02$, consistent with previous results on similar hot andmassive clusters. We confirm the excess of absorption in the direction ofA478.[abridged]Comment: 15 pages, 11 figures, accepted for publication in A&A, corrected  typo

astronomy and astrophysics

XMM-Newtonobservation of the relaxed cluster A478: Gas and dark matter distribution from 0.01R$_\mathsf{200}$ to 0.5R$\mathsf{_{200}}$