The Likely Near-Infrared Counterpart to the Anomalous X-Ray Pulsar 1E 1048.1−5937

Abstract

We report our discovery of the likely near-infrared counterpart to theanomalous X-ray pulsar (AXP) 1E 1048.1-5937, using observations from the6.5 m Baade (Magellan I) telescope in Chile. We derived a preciseposition for the X-ray source using archival data from the Chandra X-RayObservatory. This position is inconsistent with a position reported earlierfrom XMM-Newton, but we show that the originally reported XMM-Newtonposition suffered from attitude reconstruction problems. Only twoof the infrared objects in a 17 '' �17 '' fieldcontaining the target have unusual colors, and one of these has colorsconsistent with those of the identified counterparts of two otherAXPs. The latter object is also the only source detected within the0.6" Chandra error circle, and we identify it as the counterpartto 1E 1048.1-5937. This is the first AXP counterpart detected inmultiple infrared bands, with magnitudes J=21.7(3), H=20.8(3), andK=19.4(3). There is marginal evidence for spectral flattening at longerwavelengths. Based in part on observations from the 6.5 m Baade telescopeoperated by the Observatories of the Carnegie Institution of Washingtonfor the Magellan Consortium, a collaboration between the CarnegieObservatories, the University of Arizona, Harvard University, theUniversity of Michigan, and the Massachusetts Institute of Technology.