XMM-Newton discovery of 2.6 s pulsations in the soft gamma-ray repeater SGR 1627-41

After nearly a decade of quiescence, the soft gamma-ray repeater SGR 1627-41 reactivated on 2008 May 28 with a bursting episode followed by a slowly decaying enhancement of its persistent emission. To search for the still unknown spin period of this SGR taking advantage of its high flux state, we performed on 2008 September 27-28 a 120 ks long X-ray observation with the XMM-Newton satellite. Pulsations with P = 2.594578(6) s were detected at a higher than 6 sigma confidence level, with a double-peaked pulse profile. The pulsed fraction in the 2-12 keV range is 19% +/- 3% and 24% +/- 3% for the fundamental and the second harmonic, respectively. The observed 2-10 keV flux is 3.4 x 10(-13) erg cm(-2) s(-1), still a factor of similar to 5 above the quiescent pre-burstactivation level, and the spectrum is well fitted by an absorbed power law plus blackbody model (photon index Gamma similar or equal to 0.6, blackbody temperature kT similar or equal to 0.5 keV, and absorption NH approximate to 1.2 x 10(23) cm(-2)). We also detected a shell of diffuse soft X-ray emission which is likely associated with the young supernova remnant G337.0-0.1.