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

We report our discovery of the likely near-infrared counterpart to the anomalous X-ray pulsar (AXP) 1E 1048.1-5937, using observations from the 6.5 m Baade (Magellan I) telescope in Chile. We derived a precise position for the X-ray source using archival data from the Chandra X-Ray Observatory. This position is inconsistent with a position reported earlier from XMM-Newton, but we show that the originally reported XMM-Newton position suffered from attitude reconstruction problems. Only two of the infrared objects in a 17^''×17^'' field containing the target have unusual colors, and one of these has colors consistent with those of the identified counterparts of two other AXPs. The latter object is also the only source detected within the 0.6" Chandra error circle, and we identify it as the counterpart to 1E 1048.1-5937. This is the first AXP counterpart detected in multiple infrared bands, with magnitudes J=21.7(3), H=20.8(3), and K=19.4(3). There is marginal evidence for spectral flattening at longer wavelengths. Based in part on observations from the 6.5 m Baade telescope operated by the Observatories of the Carnegie Institution of Washington for the Magellan Consortium, a collaboration between the Carnegie Observatories, the University of Arizona, Harvard University, the University of Michigan, and the Massachusetts Institute of Technology.