The X–ray afterglow of the Gamma-Ray Burst GRB 030329 , associated to SN2003dh at z =0.1685 , has been observed with XMM–Newton 258 days after the burst explosion .
A source with flux of ( 6.2 \pm 2.3 ) \times 10 ^ { -16 } erg cm ^ { -2 } s ^ { -1 } ( 0.5-2 keV ) has been detected at the GRB position .
This measurement , together with a re–analysis of the previous X–ray observations , indicates a flattening of the X–ray light curve \sim 40 days after the burst .
This is in remarkable agreement with the scenario invoking the presence of two jets with different opening angles .
The wider jet should be responsible for the observed flattening due to its transition into the non–relativistic Sedov–Taylor phase .