A MID-INFRARED COUNTERPART TO THE MAGNETAR 1E 2259+586

Abstract

We report the discovery of a 4.5μm counterpart to the anomalous X-ray pulsar (magnetar) 1E 2259+586 with
\nthe Spitzer Space Telescope. The mid-infrared flux density is 6.3 ± 1.0μJy at 4.5μm and <20 μJy (at 95%
\nconfidence) at 8μm, or 0.02% of the 2–10 keV X-ray flux (corrected for extinction). Combining our Spitzer
\nmeasurements with previously published near-infrared data, we show that the overall infrared emission from 1E
\n2259+586 is qualitatively similar to that from the magnetar 4U 0142+61. Therefore, the passive X-ray-heated dust
\ndisk model originally developed for 4U 0142+61 might also apply to 1E 2259+586. However, the IR data from
\nthis source can also be fitted by a simple power-law spectrum as might be expected from magnetospheric emission.