The spin-down rate of Swift J1822.3-1606 finally measured: confirmation as magnetar
ATel #3665; L. Kuiper (SRON) and W. Hermsen (SRON, UvA)
on 27 Sep 2011; 15:00 UT
Credential Certification: Lucien Kuiper (L.M.Kuiper@sron.nl)
Subjects: X-ray, Neutron Star, Soft Gamma-ray Repeater, Transient, Pulsar
Data from monitoring observations of magnetar-candidate Swift J1822.3-1606 with RXTE PCA covering a time span of about 10 weeks (MJD 55758-55826) since its discovery on July 14, 2011 (ATEL #3488; GCN #12159) have been used to construct an accurate phase-coherent timing solution. Barycentered pulse arrival times (ToA's; see ATEL #3493 for the adopted source location) have been obtained by a cross-correlation method with a high-statistics pulse-profile template.
Fitting two frequency parameters to the ToA set (24 PCA observations) we obtained, Nu = 0.1185154236(6) Hz and dNu/dt = -3.7(5)E-15 Hz/s for Epoch 55789.0 MJD (TDB timescale; validity time range MJD 55758-55827; quoted errors are 1 sigma) consistent with the upper-limits quoted by Scholz et al. (ATEL # 3553) and Rea et al. (ATEL #3501). Monitoring observations with Swift XRT over the same period yielded consistent ToA residuals in spite of the lack of updated Swift clock correction information. The estimated surface polar magnetic field adopting the canonical magnetic-dipole braking model is (4.8+/-0.3)E13 Gauss, just above the quantum critical value of 4.413E13 Gauss.
This puts Swift J1822.3-1606 in the magnetar regime. The characteristic time scale (age) is about 5.1E5 year.
