P. Scholz, C. -Y. Ng, M. A. Livingstone, V. M. Kaspi, A. Cumming, R. Archibald
Swift J1822.3-1606 was discovered on 2011 July 14 by the Swift Burst Alert Telescope following the detection of several bursts. The source was found to have a period of 8.4377 s and was identified as a magnetar. Here we present a phase-connected timing analysis and the evolution of the flux and spectral properties using RXTE, Swift, and Chandra observations. We measure a spin frequency of 0.1185154316(5) s$^{-1}$ and a frequency derivative of $-3.5\pm0.2\times10^{-15}$ at MJD 55761.0, in a timing analysis that includes a significant non-zero second frequency derivative that we attribute to timing noise. This corresponds to an estimated spin-down inferred dipole magnetic field of $B\sim5\times10^{13}$ G, consistent with previous estimates though still possibly affected by unmodelled noise. We find that the post-outburst 1--10 keV flux evolution is well modelled with a double-exponential decay with decay timescales of $15.6\pm0.6$ and $148\pm13$ days. However we also fit the light curve with a crustal cooling model which suggests that the cooling results from heat injection into the outer crust and provides constraints on the impurity fraction in the crust. Based on proximity and similarity in absorption column density, we suggest that Swift J1822.3-1606 may have a distance comparable to that of the H{\sc ii} region M17, $1.6\pm0.3$ kpc, making it one of the closest magnetars yet known. We find that the hardness-flux correlation observed in magnetar outbursts also characterizes the outburst of Swift J1822.3-1606. We compare the properties of Swift J1822.3-1606 with those of other magnetars and their outbursts.
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http://arxiv.org/abs/1204.1034
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