The Enigmatic Binary PSR J1723-28: A Baby Millisecond Pulsar?

PSR J1723-28 is a highly-accelerated binary millisecond radio pulsar that was discovered in the Parkes Multibeam survey. Follow-up observations taken with the Parkes and Green Bank Telescopes over the past several years have yielded only occasional detections, indicating that the pulsar is highly variable. More recently, observations of the pulsar with the Green Bank Telescope using a higher observing frequency have been more successful, and a derived orbital ephemeris indicates that PSR J1723-28 has a low-mass companion (median mass of 0.3 solar masses) and a nearly circular 15-hour orbit. The pulsar's variability may be due in part to eclipsing or occasional shrouding by gas from the companion, but scintillation and intrinsic variability are also possible factors. There is a cataloged ROSAT X-ray point source within the pulsar's position uncertainty, but an association between the two objects has not yet been established. The observed features of PSR J1723-28 suggest that it may be transitioning from a low-mass X-ray binary phase into a millisecond radio pulsar phase, possibly making this a just-formed "baby millisecond pulsar", with a companion that has not yet evolved into a white dwarf. This would make PSR J1723-28 similar to the recently published J1023+0038 system. However, this is not yet certain, and additional observations are required to confirm this hypothesis. We report on our current understanding of PSR J1723-28 and our plans to try to further unravel its unusual properties.