Discovery of Hard Nonthermal Pulsed X-Ray Emission from the Anomalous X-Ray Pulsar 1E 1841–045

We report the discovery of nonthermal pulsed X-ray/soft gamma-ray emission up to ~150 keV from the anomalous 11.8 s X-ray pulsar AXP 1E 1841-045 located near the center of supernova remnant Kes 73 using Rossi X-Ray Timing Explorer (RXTE) Proportional Counter Array and High Energy X-Ray Timing Experiment (HEXTE) data. The morphology of the double-peaked pulse profile changes rapidly with energy from 2 keV up to ~8 keV, above which the pulse shape remains more or less stable. The pulsed spectrum is very hard; its shape above 10 keV can be described well by a power law with a photon index of 0.94 ± 0.16. 1E 1841-045 is the first AXP for which such very hard pulsed emission has been detected, which points to an origin in the magnetosphere of a magnetar. We have also derived the total emission spectrum from the Kes 73/1E 1841-045 complex for the ~1-270 keV energy range using RXTE HEXTE and XMM-Newton pn data. A comparison of the total emission from the complex with the pulsed+DC emission from 1E 1841-045 as derived from Chandra ACIS CC-mode data (Morii et al. 2003) leaves little room for emission from Kes 73 at energies near 7 keV or above. This suggests that the HEXTE spectrum above ~15 keV, satisfactorily described by a power law with index 1.47 ± 0.05, is dominated by emission from 1E 1841-045. In that case the pulsed fraction for energies above 10 keV would increase from about 25% near 10 keV to 100% near 100 keV. The origin of the DC-component extending up to ~100 keV is probably magnetospheric and could be a manifestation of pulsed emission that is "on" for all phases.