Centaurus X-3

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Cen X-3 is a pulsating X-ray source, believed to be an X-ray pulsar, with a period of 4.84s. It was the first X-ray pulsar to be discovered.

**Centaurus X-3**
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Centaurus X-3 (4U 1118-60) Cen X-3 was the third X-ray source to be discovered in the constellation Centaurus. It was the first pulsating X-ray source to be discovered. It was first measured during experiments of cosmic x-ray sources made on 18 May 1967. These initial x-ray spectrum and location measurements were performed using a sounding rocket. In 1971, further observations of Cen X-3 were performed with the Uhuru satellite, in the form of twenty seven 100s duration sightings. These sightings were found to pulsate with an average period of 4.84s, the scatter of these observations being only 0.02s. Later, it became clear that the transitions of the pulse period were continuous and followed a 2.09d sinusoidal fit with respect to the time predicted for a constant 4.84s period. These variations in arrival time of the pulses are attributed to Doppler shifts caused by orbital motion of the source, and although these pulse variation observations are not enough to establish a binary nature, they are a first indicator.

Cen X-3 is located in the galactic plane about 8 kpc distant, towards the direction of the Carina Spiral Arm, and is a member of an occulting spectroscopic binary system. The visible component is Krzeminski's Star, a 20.5 solar mass slightly evolved supergiant with a radius of 11.8 solar radii; the X-ray component is a compact 1 solar mass degenerate object in the form of a rotating magnetised neutron star.

X-ray loss is fuelled by accreting matter from the distended atmosphere of the blue giant spilling over at the inner Lagrangian point L1 and being sucked into the intense gravitational and magnetic fields of the neutron star.

The neutron star is regularly eclipsed by its giant companion every 2.09d, these regular X-ray eclipses lasting approximately 1/4 the orbital period. There are also sporadic X-ray off durations.

The history of Cen X-3 shows an obvious spin-up trend that is very prominent in speeding up its pulse period. This spin-up was first noted to occur in Cen X-3 and Her X-1 and is now noted in other X-ray pulsars. The most feasible way of explaining the origin of this effect is by a torque exerted of the neutron star by accreting material.