Correlated Infrared and X-Ray Flux Changes Following the 2002 June Outburst of the Anomalous X-Ray Pulsar 1E 2259+586

We present the results of a near-infrared monitoring program of the anomalous X-ray pulsar 1E 2259+586, performed at the Gemini Observatory. This program began 3 days after the pulsar's 2002 June outburst and spans ~1.5 yr. We find that after an initial increase associated with the outburst, the near-infrared flux decreased continually and reached the preburst quiescent level after about 1 yr. We compare both the near-infrared flux enhancement and its decay to those of the X-ray afterglow and find them to be remarkably consistent. Fitting simple power laws to the Rossi X-Ray Timing Explorer pulsed flux and near-infrared data for t > 1 day postburst, we find the following decay indices: α = -0.21 ± 0.01 (X-ray) and α = -0.21 ± 0.02 (near-infrared), where flux is a function of time such that F ∝ tα. This suggests that the enhanced infrared and X-ray fluxes have a physical link postoutburst, most likely from the neutron star magnetosphere.