X-rays from the nearby solitary millisecond pulsar PSR J0030+0451: The final ROSAT observations

We report on X-ray observations of the solitary 4.8 ms pulsar PSR J0030+045 1. The pulsar was one of the last targets observed in 1998 December by the ROSAT PSPC. X-ray pulses are detected on a 4.5 sigma level and make the sou rce the 11th millisecond pulsar detected in the X-ray domain. The pulsed fr action is found to be 69% +/- 18%. The X-ray pulse profile is characterized by two narrow peaks that match the gross pulse profile observed at 1.4 GHz . Assuming a Crab-like spectrum the X-ray flux is in the range f(X) = (2-3) x 10(-13) ergs s(-1) cm(-2) (0.1-2.4 keV), implying an X-ray efficiency of L-X/(E)over dot similar to (0.5-5) x 10(-3) (d/0.23 kpc)(2).