ROSAT OBSERVATIONS OF PULSED SOFT-X-RAY EMISSION FROM PSR-1055-52

Utilizing the position-sensitive proportional counter and the high-res olution imager aboard the orbiting X-ray observatory ROSAT, we have de tected pulsations at the radio period from the pulsar PSR 1055-52. The pulse shapes are energy-dependent and show a transition at approximat ely 0.5 keV where the phase angle of the pulse peak changes by approxi mately -120-degrees and the pulsed fraction increases from 11% to 63% toward larger energies. Simple spectral models are found to be unsatis factory, while multicomponent models, such as a soft blackbody and har d power-law tail, yield better fits to the pulse-height data. The hard power-law tail is consistent with the extension of the recently repor ted EGRET results and may indicate a common emission mechanism for the X-ray through GeV gamma-ray regime. The soft blackbody component with T(infinity) = (7.5 +/- 0.6) x 10(5) K, if interpreted as the initial cooling of a neutron star, is consistent with standard cooling models and does not require the presence of exotic components.