Final measure of the dipolar magnetic field of the first low-B SGR

We have recently discovered the first SGR with a low magnetic field (Rea et al.2010, Science, 330, 944), SGR 0418+5729, discovered in outburst after it emittedbursts similar to those of magnetars (B<7.5x10^{12} G). This discovery had largeimplications not only for the magnetar model, but for the pulsars population ingeneral. We have now a tentative measure (at 2.8sigma level) of its periodderivative resulting in a Bfield 7.1x10^{12} G). We ask now for a final 75ksXMM observation to confirm this detection at >5sigma. This will lead to have afinal measure of SGR 0418+5729 dipolar magnetic field, crucial for tuning themagnetar model as well as predict how many hidden magnetars there might bewithin the pulsar population. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]