A new low-B magnetar: Swift J1822.3-1606

TL;DR

This paper presents long-term X-ray observations of the newly discovered magnetar Swift J1822.3-1606, revealing its low magnetic field, spectral evolution during outburst decay, and modeling its thermal evolution to estimate its age and magnetic properties.

Contribution

It provides the first detailed timing and spectral analysis of Swift J1822.3-1606, establishing it as the second lowest magnetic field magnetar and modeling its thermal evolution.

Findings

Measured spin period of 8.43772016 s and Pdot of 8.3e-14 s/s.

Flux decreased by an order of magnitude with spectral softening.

Estimated age of approximately 550 kyr and magnetic fields Bp ~ 1.5e14 G, Btor ~ 7e14 G.

Abstract

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 182-1606), 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 Pdot = 8.3(2) x 10e-14 s s-1, which entails an inferred dipolar surface magnetic field of 2.7 x 10e13 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 Bp ~ 1.5 x 10e14 G and Btor ~ 7 x 10e14 G, respectively, and if its current age is ~550 kyr (more details in Rea et al. 2012).