Detection of pulsed X-ray emission from XMM-Newton observations of PSR J0538+2817

We report on the XMM-Newton observations of the 143 ms pulsar PSR J0538+2817. We present evidence for the first detections of pulsed X-rays from the source at a frequency that is consistent with the predicted radio frequency. The pulse pro. le is broad and asymmetric, with a pulse fraction of 18% +/- 3%. We find that the spectrum of the source is well-fitted with a blackbody with T-infinity = (2.12(-0.03)(+0. 04)) x 10(6) K and N-H = 2.5 x 10(21) cm(-2). The radius determined from the model fit of 1.68 +/- 0.05 km suggests that the emission is from a heated polar cap. A fit to the spectra with an atmospheric model reduces the inferred temperature and, hence, increases the radius of the emitting region; however, the pulsar distance determined from the fit is then smaller than the dispersion distance.