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RXTE Discovery of Coherent Millisecond Pulsations during an X-ray Burst from KS 1731-260

Donald A. Smith·Edward H. Morgan·Hale Bradt
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Abstract

A highly coherent 523.92+-0.05 Hz periodic X-ray signal has been observed during a type I X-ray burst from the low-mass X-ray binary system KS 1731-260 with the PCA on RXTE. The spectral evolution of the burst indicates photospheric-radius expansion and contraction. The 524 Hz signal occurred at the end of the contraction phase, lasted for ~2 s, was highly coherent (Q >~ 900), and had a pulse fraction (ratio of sinusoidal amplitude to mean count rate) of 6.2+-0.6%. KS 1731-260 is one of only three systems that have exhibited high-coherence millisecond oscillations during X-ray bursts and the first reported where the pulsations are associated with photospheric contraction. These coherent signals may be interpreted as a direct indication of the neutron star spin.

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Donald A. Smith, Edward H. Morgan, Hale Bradt. 1996-12-23. RXTE Discovery of Coherent Millisecond Pulsations during an X-ray Burst from KS 1731-260. https://doi.org/10.1086/310604

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