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We present Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray timingand spectroscopy of the three exceptionally energetic rotation-poweredmillisecond pulsars PSRs B1821-24, B1937+21, and J0218+4232. By correcting theNuSTAR onboard clock for phase and frequency drifts between observationintervals, we are able to recover the intrinsic hard X-ray pulse profiles ofall three pulsars with a resolution down to < 15 microsec. The substantialreduction of background emission relative to previous broadband X-rayobservations allows us to detect for the first time pulsed emission up to ~50keV, ~20 keV, and ~25 keV, for the three pulsars, respectively. We conductphase-resolved spectroscopy in the 0.5-79 keV range for all three objects,obtaining the best measurements yet of the broad-band spectral shape andhigh-energy pulsed emission to date. We find extensions of the same power-lawcontinua seen at lower energies, with no evidence for a spectral turnover orbreak. Extrapolation of the X-ray power-law spectrum to higher energies revealsthat a turnover in the 100 keV to 100 MeV range is required to accommodate thehigh-energy gamma-ray emission observed with Fermi-LAT, similar to the spectralenergy distribution observed for the Crab pulsar.

NuSTAR Hard X-ray Observations of the Energetic Millisecond Pulsars PSR B1821-24, PSR B1937+21, and PSR J0218+4232