Post-Outburst X-Ray Flux and Timing Evolution of Swift J1822.3–1606

Abstract

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 0.1185154343(8)s −1 and a frequency derivative of −4.3 ± 0.3 × 10 −15 at MJD 55761.0, in a timing analysis that include significant non-zero second and third frequency derivatives that we attribute to timing noise. This corresponds to an estimated spin-down inferred dipole magnetic field of B ∼ 5 × 10 13 G, consistent with previous estimates though still possibly affected by unmodelled noise. We find that the post-outburst 1-10 keV flux evolution can be characterized by a double-exponential decay with decay timescales of 15.5 ± 0.5 and 177 ± 14 days. We also fit the light curve with a crustal cooling model which suggests that the cooling results from heat injection into the outer crust. 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. Subject headings: pulsars: individual (Swift J1822.3−1606) -stars: neutron -X-rays: bursts -X-rays: general 2. OBSERVATIONS 2.1. Swift Observations The Swift X-Ray Telescope (XRT) consists of a Wolter-I telescope and an XMM-Newton EPIC-MOS CCD de-3 The surface dipolar component of the B-field can be estimated by B = 3.2 × 10 19 (PṖ ) 1/2 G.

The outburst decay of the low magnetic field magnetar SWIFT J1822.3−1606: phase-resolved analysis and evidence for a variable cyclotron feature

“…Based on the best fitting P andṖ , the inferred surface dipolar magnetic field is B ∼ 3.4(1) × 10 13 G at the equator. This value lies in between previous results of Scholz et al (2012): B ∼ 5 × 10 13 G, and R12: B ∼ 2.7 × 10 13 G, and is Continues below. higher than the estimate of Scholz et al (2014): B ∼ 1.4 × 10 13 G. Yet, it is lower then the BQED critical value (B ∼ 4.4 × 10 13 G): SWIFT J1822.3-1606 is thus the magnetar with the second lowest magnetic field.…”

“…For the purpose of this work a single coherent timing solution for the entire data set is desirable and we use our timing solution to perform the pulse phase-resolved analysis. We note that the timing solutions with parameters closer to ours are those reported by R12 and the 2nd solution of Scholz et al (2012), which were obtained over a time-span of ∼ 1 year.…”

“…Subsequently, the source was followed by virtually all the current generation of Xray satellites. The results of the first 9 months of X-ray monitoring of this new magnetar were presented and discussed by Rea et al (2012;hereafter R12), Scholz et al (2012) and Scholz et al (2014). In this work we perform an unprecedent coherent, pulse phase resolved spectroscopy (PPS) analysis spanning more than 400 days of outburst decay (see Fig.…”

“…Phase-averaged spectral analysis were performed by R12, Scholz et al (2012) and Scholz et al (2014). In all cases a model composed by a photoelectrically absorbed blackbody (BB) plus a power-law (PL) was used to fit the spectra; in R12 a two-BB was used as well.…”

Modelling of the surface emission of the low magnetic field magnetar SGR 0418+5729

“…Following this discovery, two more sources showing magnetar-like activity, but with "non-magnetar"-like B fields have then been discovered (Rea et al 2012;Scholz et al 2012;Rea et al 2014;Zhou et al 2014).…”