Millisecond oscillations during thermonuclear X-ray bursts

I analyze 68 oscillation trains detected in a search of 159 thermonuclear bursts from eight neutron star X-ray binaries observed with the Rossi X-ray Timing Explorer. I use all data that were public as of September 2001. The frequencies of the oscillations are uniformly distributed between 270-620 Hz, and are nearly constant for a given source. They typically have fractional rms amplitudes of 5%. During a burst, the frequencies of the oscillations generally drift upward by -4 Hz to stable limiting values. Neither the amplitudes of the oscillations nor the evolution of their frequencies are simply related to the time scales and energetics of the bursts. If the frequency drift is accounted for with smooth functions, the oscillations are coherent in 70% of the bursts, and their asymptotic frequencies are stable to a few parts in 1000. This suggests that the asymptotic frequencies are determined by the spin of the neutron star. However, residual dispersion in the frequencies from 4U 1636-536 is uncorrelated with the known orbit of the system, so some mechanism other than the orbital motion of the neutron star must cause them to vary. Models for the oscillations suggest that they originate from patterns in the stellar surface brightness that drift in the direction opposite the rotation of the neutron star, yielding oscillation frequencies lower than that of the spin. The patterns produce oscillations that are very sinusoidal - harmonic components have amplitudes that are less than 5-10% of those of the main signals. This suggests that the patterns are very symmetric. The types of bursts that exhibit oscillations are correlated with the pulsation frequency.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Physics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• Muno, Michael Patrick, 1975-

Advisor dc:contributor.advisor

• Deepto Chakrabarty.

• Physics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/8488

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/8488