High-Energy Observations of the Binary Millisecond Pulsar PSR J0218+4232

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We report the detection of pulsed X-ray emission (4.9σ) from the binary millisecond pulsar PSR J0218+4232 in a 100 ks ROSAT HRI observation. The pulse profile shows a sharp main pulse and an indication for a second weaker pulse at 0.47 phase separation. The pulsed fraction is 37 ± 13%. PSR J0218+4232 was several times in the field of view of the high-energy γ-ray telescope EGRET and a source positionally consistent with the pulsar was detected above 100 MeV. Spatial and timing analyses of EGRET data indicate that the source is probably multiple: Between 0.1 GeV and 1 GeV PSR J0218+4232 is the most likely counterpart, while the BL Lac 3C66A is the best candidate above 1 GeV. If part of the EGRET signal truly belongs to the pulsar, then this would be the first millisecond γ-ray pulsar.