THE DISCOVERY OF AN ANOMALOUS X-RAY PULSAR IN THE SUPERNOVA REMNANT KES-73

We report the discovery of pulsed X-ray emission from the compact sour ce 1E 1841-045, using data obtained with the Advanced Satellite for Co smology and Astrophysics. The X-ray source is located in the center of the small-diameter supernova remnant (SNR) Kes 73 and is very likely to be the compact stellar remnant of the supernova that formed Kes 73. The X-rays are pulsed with a period of similar or equal to 11.8 s and a sinusoidal modulation of roughly 30%. We interpret this modulation to be the rotation period of an embedded neutron star, and as such it would be the longest spin period for an isolated neutron star to date. This is especially remarkable since the surrounding SNR is very young , similar to 2000 yr old. We suggest that the observed characteristics of this object are best understood within the framework of a neutron star with an enormous dipolar magnetic field, B similar or equal to 8 x 10(14) G.