HEAD Division Meeting 1999, April 1999
Session 10. QPOs and Magnetars
Oral, Monday, April 12, 1999, 11:20am-12:44pm, Colonial Room

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[10.04] On the Frequency Evolution of Pulsations During Thermonuclear X-ray Bursts

T.E. Strohmayer, J.H. Swank (NASA/GSFC), C.B. Markwardt (NRC/GSFC), RXTE/PCA Team

We have modelled the frequency evolution of X-ray brightness oscillations seen during thermonuclear X-ray bursts. We show that a simple exponential chirp model describes well the evolution of pulse frequency and phase during the cooling tails of X-ray bursts from 4U 1728-34 and 4U 1702-429. We show that the pulse trains present in the cooling tails of bursts are highly coherent, with Q values Q \equiv \nu / \delta\nufwhm ~4000. In 4U 1728-34 and 4U 1702-429 we find universal spin-up in the cooling tails, while for 4U 1636-53 a burst with an extremely long cooling tail shows an episode of both modest spin up followed by stronger spin down. We also present evidence for initial spin-down at the rising edge of some bursts. We use our frequency evolution models to add the signals from separate bursts coherently to search for harmonics and sub-harmonics of the strongest oscillation frequency in bursts from 4U 1728-34 and 4U1 702-429. We discuss the frequency evolution in terms of rotational modulation of an angular momentum conserving thermonuclear shell.


If the author provided an email address or URL for general inquiries, it is as follows:

stroh@pcasrv1.gsfc.nasa.gov


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