A mid-infrared counterpart to the magnetar 1E 2259+586

Abstract

We report the discovery of a 4.5 μm counterpart to the anomalous X-ray pulsar (magnetar) 1E 2259+586 with the Spitzer Space Telescope. The mid-infrared flux density is 6.3 ± 1.0μJy at 4.5 μm and <20 μJy (at 95% confidence) at 8 μm, or 0.02% of the 2-10 keV X-ray flux (corrected for extinction). Combining our Spitzer measurements with previously published near-infrared data, we show that the overall infrared emission from 1E 2259+586 is qualitatively similar to that from the magnetar 4U 0142+61. Therefore, the passive X-ray-heated dust disk model originally developed for 4U 0142+61 might also apply to 1E 2259+586. However, the IR data from this source can also be fitted by a simple power-law spectrum as might be expected from magnetospheric emission.