1998/04/21 by R. Wijnands, Rudy Wijnands, Wijnands, Rudy +3
Physics and Astronomy · #Astrophysical Phenomena and Observations #Gamma-ray bursts and supernovae #Pulsars and Gravitational Waves Research #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9804216
Submitted to Nature on April 20, 1998. Press embargo until publication. 12 pages, including 3 figures
arxiv created 1998/04/21 · arxiv updated 2009/12/01
The precise origins of the millisecond radio pulsars, discovered in the early 1980s, remain uncertain until this day. They plausibly evolve from accreting low magnetic-field neutron stars in X-ray binary systems. If so, these stars should spin at millisecond rates. In accordance with this idea, quasi-periodic oscillations discovered in X-ray binaries around 50 Hz and 1 kHz, and drifting oscillations at several 100 Hz in X-ray bursts have all been interpreted in terms of millisecond spins of weakly magnetized neutron stars. However, in 15 years of searching, the expected coherent millisecond signals from X-ray binaries remained elusive. In this Letter, we report the discovery of the first example of such a signal. Using the Rossi X-ray Timing Explorer we find persistent 2.49 millisecond X-ray pulsations in an X-ray binary, which we interpret to come from an accretion-powered millisecond X-ray pulsar in the system. This is the first known object of its kind. It is likely to switch on as a millisecond radio pulsar when the accretion turns off completely. The source is positionally coincident with the known transient X-ray burster SAX J1808.4-3658, which also makes this the first X-ray pulsar which exhibits thermonuclear X-ray bursts.