High-resolution spatial and timing observations of millisecond pulsar PSR J0218+4232 with Chandra

We report on high-resolution spatial and timing results for binary millisecond pulsar PSR J0218+4232 obtained with the Chandra HRC-I and HRC-S in imaging mode. The subarcsecond resolution image of the HRC-I (0.08-10 keV) showed that the X-ray emission from PSR J0218+4232 is consistent with that of a point source, excluding the presence of a compact nebula with a size of about 14" for which we had indications in ROSAT HRI data. The presence of a DC component is confirmed. This X-ray DC component has a softer spectrum than the pulsed emission and can be explained by emission from a heated polar cap. With our HRC-S observation, we obtained a 0.08-10 keV pulse pro le with high statistics showing the well-known double-peaked morphology in more detail than before: the two pulses have broad wings, and pulsed emission appears only to be absent in a narrow phase window of width less than or similar to0.1. The absolute timing accuracy of similar to200 mus makes it possible to compare for the first time in absolute phase the X-ray pulse profile with the highly structured radio profile and the high-energy gamma-ray profile (0.1-1 GeV). The two X-ray pulses are aligned within absolute timing uncertainties with two of the three radio pulses. Furthermore, the two gamma-ray pulses are aligned with the two nonthermal X-ray pulses, corresponding to a probability for a random occurrence of 4.9 sigma, strengthening the credibility of the earlier reported first detection of pulsed high-energy gamma-ray emission from this millisecond pulsar.