2008ApJ...678L..43K

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 (E{dot} = 8.3x10³⁶ ergs/s) among all the high magnetic field pulsars (HBPs) and has been classified as a Crab-like pulsar despite its magnetic field (5x10^ 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)x10^–12 to 2.7^+0.1_–0.2 x10^–11 ergs/cm2/s] 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)x10³⁴ to 1.16^+0.03_–0.07 x10³⁵ ergs/s, 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.