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 sub-arcsecond 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 profile 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 ∼< 0.1. The absolute timing accuracy of ∼ 200μs 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 γ-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 γ-ray pulses are aligned with the two non-thermal X-ray pulses, corresponding to a probability for a random occurrence of 4.9σ, strengthening the credibility of the earlier reported first detection of pulsed high-energy γ-ray emission from a (this) millisecond pulsar. Subject headings: pulsars: individual (PSR J0218+4232 ), X-rays: stars