Post-Outburst Observations of the Magnetically Active Pulsar J1846–0258. A New Braking Index, Increased Timing Noise, and Radiative Recovery

The ∼800 year old pulsar J1846−0258 is a unique transition object between rotation-powered pulsars and magnetars: though behaving like a rotation-powered pulsar most of the time, in 2006 it exhibited a distinctly magnetar-like outburst accompanied by a large glitch. Here, we present X-ray timing observations taken with the Rossi X-ray Timing Explorer over a 2.2 year period after the X-ray outburst and glitch had recovered. We observe that the braking index of the pulsar, previously measured to be n = 2.65 ± 0.01, is now n = 2.16 ± 0.13, a decrease of 18% ± 5%. We also note a persistent increase in the timing noise relative to the pre-outburst level. Despite the timing changes, a 2009 Chandra X-ray Observatory observation shows that the X-ray flux and spectrum of the pulsar and its wind nebula are consistent with the quiescent levels observed in 2000.