SIMBAD references

We report on X-ray observations of the solitary 4.8 ms pulsar PSR J0030+0451. 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 σ level and make the source the 11th millisecond pulsar detected in the X-ray domain. The pulsed fraction 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)x10^–13 ergs.s^–1.cm^–2 (0.1-2.4 keV), implying an X-ray efficiency of L_X/E{dot}~(0.5-5)x10^–3(d/0.23 kpc)².