On the Spin History of the X-ray Pulsar in Kes73: Further Evidence for an Utramagnetized Neutron Star

In previous papers, we presented the discovery of a 12-s X-ray pulsar in the supernova remnant Kes 73 providing the first direct evidence for an ultramagnetized neutron star, a magnetar, with an equivalent dipole field of nearly twenty times the quantum critical magnetic field (mec /eh̄). Our conclusions were based on two epochs of measurement of the spin, along with an age estimate of the host supernova remnant. Herein, we present a spin chronology of the pulsar using additional Ginga, ASCA, RXTE, & BeppoSAX datasets spanning over a decade. Timing and spectral analysis confirms our initial results and severely limit an accretion origin for the observed flux. Over the 10 year baseline, the pulsar is found to undergo a rapid, constant spindown, while maintaining a steady flux and an invariant pulse profile. Within the measurement uncertainties, no systematic departures from a linear spin-down are found departures as in the case of glitches or simply stochastic fluctuations in the pulse times-of-arrival (e.g. red timing noise). We suggest that this pulsar is akin to the soft γ-ray repeaters, however, it is remarkably stable and has yet to display similar outbursts; future γ-ray activity from this object is likely. Subject headings: stars: individual (Kes 73, 1E1841−045) — stars: neutron — supernova remnants — X-rays: stars