HEAD Division Meeting 1999, April 1999
Session 38. Neutron Star Binaries
Oral, Thursday, April 15, 1999, 2:00pm-3:31pm, Colonial Room

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[38.02] Detection of 3.3 and 6.5 Millisecond Pulsations from Type I\\X-ray Bursts of the Rapid Burster

D.W. Fox (MIT), R.E. Rutledge (Caltech), W.H.G. Lewin, E.H. Morgan (MIT), R. Guerriero (US Military Academy), M. van der Klis (UC Berkeley and Astr. Inst. `Anton Pannekoek'), J. van Paradijs (Astr. Inst. `Anton Pannekoek' and UA Huntsville), C.B. Moore (Kapteyn Inst.), L. Bildsten (UC Berkeley), T. Dotani, K. Asai (ISAS)

We report the detection of 3.26 and 6.46 millisecond pulsations in the rising portion of type I X-ray bursts of MXB 1730-335, the Rapid Burster. The signals are initially detected in the summed power density spectrum of 31 one-second intervals taken from the burst rise of each of 31 type I X-ray bursts observed with the \textit{Rossi X-ray Timing Explorer} satellite (5.5--16 keV flux only), and together are significant at the 3.7 sigma level. Inspection of the individual bursts shows that the 3.26 and 6.46 millisecond signals are strongest in different bursts; therefore, the imperfect harmonic relationship of the two frequencies may be the result of drifts in oscillation frequency during the bursts, as have been seen in other burst sources. In accordance with similar results from other low-mass X-ray binaries, we suggest that our finding indicates a neutron star spin period of approximately 6.5 milliseconds for the Rapid Burster.

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