New observational constraints on hard X-/γ-ray millisecond pulsar emission from 47 Tucanae

Recent X-/gamma-ray observations with the Rossi X-ray Timing Explorer (RXTE) of 47 Tuc (NGC 104) are used to compare different models of millisecond pulsar emission. Data from both the Proportional Counter Array and the High Energy X-ray Timing Experiment are presented, covering a total energy range of 2-250 keV. A new upper limit on the hard X-/gamma-ray emission from 47 Tuc is set, suggesting that the isolated millisecond pulsars may be non-emitting or very weak X-ray sources. The current binary X-ray emission theory is consistent with this result with some modification. Timing analysis reveals no periodic pulsations in the data, further suggesting that isolated millisecond pulsars are very weak X-ray emitters.