The Broadband Spectrum and Infrared Variability of the Magnetar AXP 1E 1048.1−5937

We present photometry of the Anomalous X-ray pulsar 1E1048.1-5937 in theinfrared and optical, taken at Magellan and the VLT. The object is detected inthe I, J and Ks bands under excellent conditions. We find that the source hasvaried greatly in its infrared brightness and present these new magnitudes. Nocorrelation is found between the infrared flux and spin-down rate, but theinfrared flux and X-ray flux may be anti-correlated. Assuming nominal reddeningvalues, the resultant spectral energy distribution is found to be inconsistentwith the only other AXP SED available (for 4U0142+61). We consider the effectof the uncertainty in the reddening to the source on its SED. We find thatalthough both the X-ray and infrared fluxes have varied greatly for thissource, the most recent flux ratio is remarkably consistent with what is isfound for other AXPs. Finally, we discuss the implications of our findings inthe context of the magnetar model.Comment: 21 pages, 5 eps figures. Submitted to Ap