XMM-Newton observation of the double pulsar system J0737-3039

We report on a 50 ks XMM-Newton observation of the double pulsar system J0737-3039 performed in 2004 April. We present results of the spectral analysis of these data combined with the much shorter Chandra pointing performed in 2004 January. Blackbody emission with an effective temperature of 0.20(-0.02)(+0.02) keV (90% confidence level) and emission radius 75(-9)(+30) m for a distance of 0.5 kpc (implying a 0.5-10 keV luminosity similar to6x10(29) ergs s(-1)) is a viable interpretation, calling for a stream of particles accelerated in the magnetosphere of PSR J0737-3039A and depositing their kinetic energy in the magnetic polar cap of PSR J0737-3039A or of the companion PSR J0737-3039 B. A single power-law emission model implies a very steep photon index Gamma=4.2(-1.2)(+2.1) and a suspiciously high hydrogen column density, whereas a photon index Gamma=2 does not provide an adequate description of the XMM-Newton and Chandra data. A two-component model (a blackbody plus a power law with Gamma=2) is statistically acceptable, but the additional power-law component is not required by the data.