We report on the long term X-ray monitoring with Swift , RXTE , Suzaku , Chandra , and XMM–Newton of the outburst of the newly discovered magnetar Swift J1822.3–1606 ( SGR 1822-1606 ) , from the first observations soon after the detection of the short X-ray bursts which led to its discovery ( July 2011 ) , through the first stages of its outburst decay ( April 2012 ) .
Our X-ray timing analysis finds the source rotating with a period of P = 8.43772016 ( 2 ) s and a period derivative \dot { P } = 8.3 ( 2 ) \times 10 ^ { -14 } s s ^ { -1 } , which entails an inferred dipolar surface magnetic field of B \simeq 2.7 \times 10 ^ { 13 } G at the equator .
This measurement makes Swift J1822.3–1606 the second lowest magnetic field magnetar ( after SGR 0418 + 5729 ; Rea et al .
2010 ) .
Following the flux and spectral evolution from the beginning of the outburst , we find that the flux decreased by about an order of magnitude , with a subtle softening of the spectrum , both typical of the outburst decay of magnetars .
By modeling the secular thermal evolution of Swift J1822.3–1606 , we find that the observed timing properties of the source , as well as its quiescent X-ray luminosity , can be reproduced if it was born with a poloidal and crustal toroidal fields of B _ { p } \sim 1.5 \times 10 ^ { 14 } G and B _ { tor } \sim 7 \times 10 ^ { 14 } G , respectively , and if its current age is \sim 550 kyr ( Rea et al .
2012 ) .