THE 1.24 s X-ray pulses observed in the 2-20 keV region from Her X-1 are thought to arise from matter being accreted on to a rotating, magnetic neutron star. The pulse shape has been studied by several groups1-3. More than 65% of the emission is concentrated in 0.4 of the duty cycle. The emission in this interval is usually double peaked, though it is sometimes single peaked1 or asymmetrical2,3. The pulse profile varies on time-scales of hours to days1, and from pulse to pulse (my unpublished work with T. Chetim and R. Giacconi).
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