Variability of the High Magnetic Field X-Ray Pulsar PSR J1846-0258 Associated with the Supernova Remnant Kes 75 as Revealed by the Chandra X-Ray Observatory

We present results from the archival Chandra observations of the 0.3 s X-ray pulsar PSR J1846–0258 associated with the supernova remnant (SNR) Kes 75. The pulsar has the highest spin-down luminosity ( = 8.3 × 10 36 ergs s −1 ) among all the high magnetic field pulsars (HBPs) and has been classified as a Crab-like pulsar despite its magnetic field (5 × 10 13 G) being above the quantum critical field. It is the only HBP described by a nonthermal Crab-like spectrum, powering a bright pulsar wind nebula (PWN). Our spectroscopic study shows evidence of spectral softening (photon index Γ = 1.32 + 0.08 −0.09 to 1.97 + 0.05 −0.07 ) and temporal brightening [unabsorbed flux F unabs = (4.3 ± 0.2) × 10 −12 to 2.7 −0.2 +0.1 × 10 −11 ergs cm −2 s −1 ] of the pulsar by ~6 times from 2000 to 2006. The 0.5-10 keV luminosity of the pulsar at the revised distance of 6 kpc has also increased from L X = (1.85 ± 0.08) × 10 34 to 1.16 + 0.03 −0.07 × 10 35 ergs s −1 , and the X-ray efficiency increased from 0.2% ± 0.01% to 1.4 + 0.04 −0.08 % . The observed X-ray brightening and softening of the pulsar suggests for the first time that this HBP is revealing itself as a magnetar.