On 2011 July 14, a new magnetar candidate, Swift J1822.3-1606, was identified via a rate trigger on the Swift/Burst Alert Telescope. Here we present an initial analysis of the X-ray properties of the source, using data from the Rossi X-ray Timing Explorer, Swift, and the Chandra X-ray Observatory, spanning 2011 July 16--September 22. We measure a precise spin period of P=8.43771963(5) s and a spin-down rate of 2.97(28)E-13, at MJD 55761.0, corresponding to an inferred surface dipole magnetic field strength of B=5.1E13 G, the second lowest thus far measured for a magnetar, though similar to 1E~2259+586 as well as to several high-magnetic field radio pulsars. We show that the pulsed X-ray flux decay in the 2--10 keV band is best fit by an exponential with a time constant of 16.4+/-0.3 days. After increasing from ~35% during the first week after the onset of the outburst, the pulsed fraction in the 2--10 keV band remained constant at ~45. We argue that these properties confirm this source to be a new member of the class of objects known as magnetars.
@article{arxiv.1109.5715,
title = {The Spin-down of Swift J1822.3-1606: A New Galactic Magnetar},
author = {Margaret A. Livingstone and Paul Scholz and Victoria M. Kaspi and C. -Y. Ng and Fotis P. Gavriil},
journal= {arXiv preprint arXiv:1109.5715},
year = {2015}
}
Comments
7 pages, 3 figures. Submitted to the Astrophysical Journal Letters