Is SGR 0418+5729 indeed a waning magnetar ?

Understand

SGR 0418+5729 is a transient Soft Gamma-ray Repeater which underwent a major outburst in June 2009, during which the emission of short bursts was observed.

• Its properties appeared quite typical of other sources of the same class until long-term X-ray monitoring failed to detect any period derivative.
• The present upper limit on $\dot P$ implies that the surface dipole field is $B_p\lesssim 7.5\times 10^{12}\ {\rm G}$ (Rea et al 2010), well below those measured in other Soft Gamma-ray Repeaters (SGRs) and in the Anomalous X-ray Pulsars (AXPs), a group of similar sources.
• Both SGRs and AXPs are currently believed to be powered by ultra-magnetized neutron stars (magnetars, $B_p\approx 10^{14}$--$10^{15}\ {\rm G}$).