The Infrared Counterpart to the Magnetar 1RXS J170849.0–400910

We have analyzed both archival and new infrared imaging observations of the field of the anomalous X-ray pulsar (AXP) 1RXS J170849.0-400910, in search of the infrared counterpart. This field has been previously investigated, and one of the sources consistent with the position of the AXP has been suggested as the counterpart. We, however, find that this object is more likely a background star, while another object within the positional error circle has nonstellar colors and shows evidence for variability. These two pieces of evidence, along with a consistency argument for the X-ray-to-infrared flux ratio, point to the second source being the more likely infrared counterpart to the AXP.